External Cavity Diode Laser Controller

Transcription

1 External Cavty Dode Laser Controller DLC102, DLC202, DLC252, DLC502 Revson 9.09

2 Lmtaton of Lablty MOG Laboratores Pty Ltd (MOGLabs) does not assume any lablty arsng out of the use of the nformaton contaned wthn ths manual. Ths document may contan or reference nformaton and products protected by copyrghts or patents and does not convey any lcense under the patent rghts of MOGLabs, nor the rghts of others. MOGLabs wll not be lable for any defect n hardware or software or loss or nadequacy of data of any knd, or for any drect, ndrect, ncdental, or consequental damages n connectons wth or arsng out of the performance or use of any of ts products. The foregong lmtaton of lablty shall be equally applcable to any servce provded by MOGLabs. Copyrght Copyrght c MOG Laboratores Pty Ltd (MOGLabs) No part of ths publcaton may be reproduced, stored n a retreval system, or transmtted, n any form or by any means, electronc, mechancal, photocopyng or otherwse, wthout the pror wrtten permsson of MOGLabs. Contact For further nformaton, please contact: MOG Laboratores P/L 18 Boase St Brunswck VIC 3056 AUSTRALIA nfo@moglabs.com MOGLabs USA LLC th St Huntngdon PA USA nfo@moglabsusa.com MOGLabs Europe Goethepark Berln Germany chrstoph.p@moglabs.com

3 Preface Dode lasers can be wonderful thngs: they are effcent, compact, low cost, hgh power, low nose, tunable, and cover a large range of wavelengths. They can also be obstreperous, senstve, and temperamental, partcularly external cavty dode lasers (ECDLs). The mechancs and optcs needed to turn a smple $ mw AlGaAs dode laser nto a research-qualty narrow-lnewdth tunable laser are farly straghtforward [1, 2, 3, 4], but the electroncs s demandng and, untl now, not avalable commercally from a sngle suppler, let alone n a sngle unt. The MOGLabs range of ECDL controllers change that. Wth each DLC unt, we provde everythng you need to run your ECDL, and lock t to an atomc transton. In addton to current and temperature controllers, we provde pezo drvers, sweep ramp generator, modulator for AC lockng, lock-n amplfer, feedback servo system, laser-head electroncs protecton board, even a hgh-speed low-nose balanced photodetector. We would lke to thank the many people that have contrbuted ther hard work, deas, and nspraton. We hope that you enjoy usng the DLC as much as we do. Please let us know f you have any suggestons for mprovement n the DLC or n ths document, so that we can make lfe n the laser lab easer for all, and check our webste from tme to tme for updated nformaton. MOGLabs

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5 Safety Precautons Safe and effectve use of ths product s very mportant. Please read the followng safety nformaton before attemptng to operate your laser. Also please note several specfc and unusual cautonary notes before usng the MOGLabs DLC, n addton to the safety precautons that are standard for any electronc equpment or for laser-related nstrumentaton. CAUTION USE OF CONTROLS OR ADJUSTMENTS OR PERFORMANCE OF PROCEDURES OTHER THAN THOSE SPECIFIED HEREIN MAY RESULT IN HAZARDOUS RADIATION EXPOSURE Laser output can be dangerous. Please ensure that you mplement the approprate hazard mnmsatons for your envronment, such as laser safety goggles, beam blocks, and door nterlocks. MOGLabs takes no responsblty for safe confguraton and use of your laser. Please: Avod drect exposure to the beam. Avod lookng drectly nto the beam. Note the safety labels and heed ther warnngs. When the laser s swtched on, there wll be a short delay of two seconds before the emsson of laser radaton, mandated by European laser safety regulatons (IEC ). The STANDBY/RUN keyswtch must be turned to RUN before the laser can be swtched on. The laser wll not operate f the keyswtch s n the STANDBY poston. The key cannot be

6 v removed from the controller when t s n the clockwse (RUN) poston. To completely shut off power to the unt, turn the keyswtch ant-clockwse (STANDBY poston), swtch the mans power swtch at rear of unt to OFF, and unplug the unt. When the STANDBY/RUN keyswtch s on STANDBY, there cannot be power to the laser dode, but power s stll beng suppled to the laser head for temperature control. CAUTION Please ensure that the unt s confgured for the correct voltage for your AC mans supply before connectng. The supply must nclude a good ground connecton. CAUTION To ensure correct coolng arflow, the unt should not be operated wth cover removed. WARNING The nternal crcut boards and many of the mounted components are at hgh voltage, wth exposed conductors, n partcular the hgh-voltage pezo drver crcutry. The unt should not be operated wth cover removed. NOTE The MOGLabs DLC s desgned for use n scentfc research laboratores. It should not be used for consumer or medcal applcatons.

7 Protecton Features The MOGLabs DLC ncludes a number of features to protect you and your laser. Softstart A tme delay (3 s) followed by lnearly rampng the dode current (3 s max). Crcut shutdown Many areas of the crcutry are powered down when not n use. The hgh voltage supply and pezo drvers, the dode current supples, the col drver, and others are wthout power when the unt s n standby mode, f an nterlock s open, or a fault condton s detected. Current lmt Sets a maxmum possble dode njecton current, for all operatng modes. Note that current suppled through the RF connector on the laser headboard s not lmted. Cable contnuty If the laser s dsconnected, the system wll swtch to standby and dsable all laser and pezo power supples. If the laser dode, TEC or temperature sensor fal and become open-crcut, they wll be dsabled accordngly. Short crcut If the laser dode, TEC or temperature sensor fal and become short-crcut, or f the TEC polarty s reversed, they wll be dsabled accordngly. Temperature If the detected temperature s below 5 C or above 35 C, the temperature controller s dsabled. Internal supples If any of the nternal DC power supples (+5, ±10, ±12 V) s 1 V or more below ts nomnal value, the respectve components (temperature controller, dode current supply) are dsabled. v

8 v Protecton relay When the power s off, or f the laser s off, the laser dode s shorted va a normally-closed sold-state relay at the laser head board. Emsson ndcator The MOGLabs controller wll llumnate the emsson warnng ndcator LED mmedately when the laser s swtched on. There wll then be a delay of at least 2 seconds before actual laser emsson. Mans flter Protecton aganst mans transents. Key-operated The laser cannot be powered unless the key-operated STANDBY swtch s n the RUN poston, to enable protecton aganst unauthorsed or accdental use. The key cannot be removed from the controller when t s n the clockwse (RUN) poston. Interlocks Both the man unt and the laser head board have nterlocks, to allow dsablng of the laser va a remote swtch, or a swtch on the laser cover.

9 Contents Preface Safety Precautons Protecton Features 1 Introducton Basc operaton Passve frequency control DC lockng to an atomc transton AC lockng to an atomc transton Connectons and controls Front panel controls Front panel dsplay/montor Rear panel controls and connectons Internal swtches and adjustments Feedback confguratons Dgtal control Internal trmpots Operaton Smplest confguraton Laser frequency control External scan control Lockng to an atomc transton: DC Lockng to an atomc transton: AC External sweep Lockng usng an external sgnal v v

10 v Contents 3.8 External control of lock frequency setpont Optmsaton Frequency reference Nose spectra A Specfcatons 41 A.1 RF response A.2 Sweep saturaton and trgger B Troubleshootng 47 B.1 STANDBY/RUN ndcator B.2 Dode OFF/ON ndcator B khz modulaton B.4 Lockng C Usng DBR/DFB dodes 53 C.1 Fne current control C.2 DC current feedback C.3 Slow current feedback C.4 Lock saturaton C.5 Specal optons D Modulaton cols 55 D.1 Feld requrements D.2 Col mpedance D.3 Impedance matchng D.4 Tunng D.5 Sheldng E External modulators and njecton current modulaton 61 E.1 Couplng crcut E.2 Injecton current modulaton F Photodetector 65 F.1 Photododes G Laser head board 67 G.1 Headboard connectors G.2 Dual pezo operaton

11 Contents x G.3 RF couplng H Feedback overvew 71 I Connector pnouts 75 I.1 Laser I.2 Photodetector I.3 Interlock I.4 Dgtal control J PCB layout 79 K 115/230 V converson 81 K.1 Fuse K.2 120/240 V converson References 86

12 x Contents

13 SET 1. Introducton The MOGLabs DLC can be used n varous confguratons, ncludng smple current/temperature controller, passve frequency controller wth nternal or external sweep/scan, and as a complete system for actve frequency stablsaton wth AC, DC or external lockng sgnal. Here s a quck outlne of some modes of operaton, so that you can connect and go as quckly as possble. Detals are provded n chapter Basc operaton In the smplest confguraton, the MOGLabs DLC wll be used to control the dode njecton current, and temperature. All connectons are va a sngle cable to the MOGLabs laser. If usng wth a non- MOGLabs laser, please see appendx G for nformaton on connectng the dode, thermoelectrc Pelter cooler (TEC), and temperature sensor va the laser head nterface board whch s provded. For operaton wth DBR/DFB dodes, please see appendx C. The front-panel dsplay and selector swtch can be used to montor the dode current, current lmt, dode dropout voltage, temperature, temperature setpont, and TEC current; see fgure 1.1. DIODE Dode Laser Controller SCAN FEEDBACK MONITOR ma A V C Voltage Curr Temp set max Current Temperature Frequency TEC current TEC voltage CURRENT FREQUENCY INPUT SPAN PHASE ERROR OFFSET GAIN SLOW FAST Freq Flter Slow Current Error Mod STANDBY RUN OFF ON T BIAS OFF MOD SCAN LOCK OFF LOCK Input Fast Input Temp A CHANNEL B Fgure 1.1: MOGLabs DLC front panel layout. 1

14 2 Chapter 1. Introducton 120V STACK FREQUENCY SPAN 0V 5V 0V TRIG tme Fgure 1.2: Stack (or current bas) output and trgger pulse, when scannng. Note that the ramp slope can be nverted. Detals of the ramp behavour are descrbed n secton A Passve frequency control The MOGLabs DLC controls the laser frequency va the dode current, and pezo electrc actuators to control the cavty length of an ECDL. In normal (SCAN) mode, a sawtooth s suppled to the man (STACK) actuator to lnearly sweep the laser frequency at a rate determned by the rear-panel trmpot, fsweep, from 4 to 70 sweeps per second; see fgure 1.2. Crtcal DLC sgnals can be montored usng the CHANNEL A and CHANNEL B outputs on the rear panel, synchronsed to the TRIG trgger output, whch should be connected to the equvalent nputs on a two-channel osclloscope. The partcular sgnals are selected from the front-panel CHAN A and CHAN B selector swtches. The sgnals are descrbed n detal n the followng chapter. Fgure 1.3 s an example of what s seen on the osclloscope n a smple scannng confguraton. The laser beam transmtted by an atomc vapour cell s detected on the photodetector provded wth the controller, as the laser frequency sweeps through atomc resonances, thus showng the atomc absorpton spectrum. The FREQUENCY knob controls the offset to the pezo-electrc actu-

15 1.2 Passve frequency control 3 C1 C2 Ch1 100mV Ch2 100mV 5.0ms Fgure 1.3: A smple absorpton spectrum of rubdum wth the controller n smple frequency scannng mode. ator (STACK) and thus the md-pont frequency of the sweep. As the external cavty frequency changes, the laser may mode-hop due to competton between the external cavty and the nternal cavty defned by the rear and front facets of the dode saemconductor chp tself. The nternal frequency of the dode can be adjusted by changng the dode current, ether manually as the FREQUENCY offset s adjusted when modehops are observed. The current can also be automatcally based durng the frequency sweep, f BIAS s enabled va the nternal DIP swtch 4. Note that adjustng the frequency offset (FREQUENCY knob) wll affect the dode current f BIAS s enabled, but t may stll be necessary to adjust the dode current as FREQUENCY s adjusted, to avod modehops. The extent of the frequency sweep s controlled wth the SPAN control. The maxmum range s typcally GHz. Dependng on the offset, the span may be lmted by the mnmum and maxmum voltage that can be appled to the actuator, as descrbed n detal n secton A.2.

16 4 Chapter 1. Introducton 1.3 DC lockng to an atomc transton Fgure 1.4 shows one possble confguraton n whch a MOGLabs DLC s used to lock an ECDL to an atomc transton. Lockng s to the sde of an absorpton peak n a vapour cell; see for example Demtröder [5] for more nformaton on spectroscopy. The passve confguraton of 1.2 s extended wth the MOGLabs DLC photodetector (see appendx F), and an atomc vapour absorpton cell. Alternately, a Fabry-Perot optcal cavty or other reference could be used. M M BS λ/4 λ/4 Vapour cell BS PD BS ECDL Servo Offsets Fgure 1.4: Schematc setup for DC lockng to an atomc transton. PD s the DLC photodetector. BS beamspltter, M mrror, λ/4 a quarter-wave retarder. The schematc shows a saturated absorpton spectroscopy arrangement, but often smply lockng to the sde of a Doppler-broadened absorpton peak wll be adequate. The photodetector can be used n sngle channel mode (default) or wth balanced dfferental nputs, for example to subtract a Doppler background from a saturated absorpton spectrum. The lock frequency s determned by the zero-crossng pont of the photosgnal. The photosgnal offset s adjusted va the INPUT OFFSET and ERROR OFFSET controls. Feedback can be va one or both pezo actuators, or the dode njecton current, or all three.

17 1.4 AC lockng to an atomc transton AC lockng to an atomc transton Wth AC lockng (FM demodulaton or lock-n amplfer detecton), the laser frequency can be locked to a peak centre. The AC approach offers the advantage of nherently lower detected nose and thus the potental for mproved laser frequency stablty. The setup s smlar to that for DC lockng, but modulaton of the laser frequency, or the reference frequency, s requred. The MOGLabs DLC provdes an nternal 250 khz oscllator whch can drectly dther the dode current, or drve an external modulator. In partcular, t s desgned to drve a Zeeman-shft modulaton col surroundng the atomc reference vapour cell; see appendx D. Fgures 1.5, 3.5, 3.6 show examples of AC lockng arrangements, usng a col to Zeeman-modulate the atomc reference, or an acoustooptc modulator (AOM) for modulatng the frequency of the beam passng through the vapour cell. If preferred, the modulator oscllator can be set to dther the dode current (see 2.4). Feedback can agan be va one or both pezo actuators, the dode current, or all three. M M BS Vapour cell + col λ/4 λ/4 AOM BS PD f ~ 150mm f ~ 25mm 250kHz BS ECDL Servo Lock-n Fgure 1.5: Setup for AC lockng to an atomc transton. PD DLC photodetector, BS beamspltter, M mrror, λ/4 quarter-wave retarder. See also Fgs. 3.5, 3.6.

18 6 Chapter 1. Introducton

19 SET 2. Connectons and controls 2.1 Front panel controls DIODE Dode Laser Controller SCAN FEEDBACK MONITOR ma A V C Curr Temp Voltage max set Current Temperature Frequency TEC current TEC voltage CURRENT FREQUENCY INPUT SPAN PHASE ERROR OFFSET GAIN SLOW FAST Flter Freq Slow Current Error Mod STANDBY RUN OFF ON T BIAS OFF MOD SCAN LOCK OFF LOCK Input Fast Input Temp A CHANNEL B STANDBY/RUN OFF/ON In STANDBY mode, the DLC mantans the laser temperature, but powers down all other components ncludng the hgh-voltage pezo power, and the man on-board low-voltage power. In RUN mode, the DLC actvates all crcuts, ncludng the laser current drver and pezo drvers. The dode current s dsabled, and the STACK s on but not scannng, untl the laser enable swtch s ON. On frst power-up, the STANDBY ndcator wll be red; ths s normal and ndcates there has been a power falure snce last swtched to RUN. The unt should then be set to RUN to ntate temperature control, and back to STANDBY f further operaton s not desred. If the unt fals to swtch to RUN mode (ndcator does not show green), see appendx B. Dode njecton current enable. Also actvates the STACK ramp and current bas (f DIP swtch 4 n ON). The STANDBY/RUN key swtch must frst be on RUN and the assocated ndcator must be green. If the unt fals to swtch to RUN mode (ndcator does not show green), see appendx B. 7

20 8 Chapter 2. Connectons and controls CURRENT FREQUENCY Note Dode njecton current, 0 to 100/200/250/500 ma (DLC102 to DLC502). The response s not lnear; that s, the change n current vares for a gven rotaton of the knob. The md-range senstvty s reduced to allow greater precson at normal operatng currents. The laser frequency wll normally be controlled va a multlayer pezo-electrc actuator (STACK). Ths knob controls the offset voltage appled to that actuator, 0 to 120 V (or 150 V; see LK2, p. 15). For DFB/DBR dodes, the frequency control feedback sgnal can control the dode current rather than the stack; see 2.4, DIP swtch 16. The FREQUENCY control wll also affect the dode current, f BIAS (DIP swtch 4) s enabled. SPAN Frequency scan range, from 0 to 120 V (or 150 V; see LK2, p. 15). The span may be lmted by the mnmum and maxmum voltage that can be appled to the actuator; see detaled descrpton n secton A.2. PHASE GAIN SLOW FAST T set BIAS When AC lockng, the controller demodulates the error sgnal from the detected lght ntensty. PHASE adjusts the relatve phase between the nternal reference modulator and the detected sgnal, from 0 to 360. When DC lockng, the sgn of the error sgnal can be flpped by rotatng the PHASE control. Overall error sgnal gan, 0 to 40 db. Gan for feedback to the slow (pezo) actuator, 0 to 40 db. Gan for fast feedback to the dode current, 0 to 40 db. Temperature set pont, 0 30 standard; extended range optonal. Feed-forward bas current. If DIP swtch 4 s ON, changes n laser frequency, usually va the STACK actuator, wll smultaneously change the current. Ths trmpot controls the slope di/df of current wth frequency. It can be postve or negatve, wth a range of ±25 ma for the full frequency span.

21 2.1 Front panel controls 9 INPUT OFFSET OFF/MOD Offset of nput lght ntensty sgnal, 0 to 10 V. Ths can be adjusted to brng the photodetector lght sgnal close to zero on the osclloscope, and to shft the zero frequency lockpont for DC lockng. Modulator enable, to swtch on the col drver, dode current dther, or external modulator. ERROR OFFSET Offset of the frequency error lock sgnal. The DLC wll lock such that the error sgnal plus ERROR OFFSET s zero, allowng for small adjustment of the lock frequency. SCAN/LOCK Swtch between scannng mode and lock mode. When swtchng from scan to lock, the controller wll frst reset the scannng actuator (usually STACK) to the offset voltage at the trgger pont, and then lock to the nearest frequency at whch the error sgnal s zero. +/ OFF/LOCK Sgn of fast (current) feedback. The sgn of the slow feedback can be changed wth the PHASE control, for both AC and DC lockng. Enable fast (current) feedback. The laser can be locked wth slow (pezo) lockng or fast (current) lockng alone. Best performance s usually obtaned wth both channels of feedback; see chapter 4 for feedback optmsaton.

22 10 Chapter 2. Connectons and controls 2.2 Front panel dsplay/montor Dsplay selector The MOGLabs DLC ncludes a hgh-precson 4.5 dgt LED dsplay wth four unt annuncators and 8-channel selector swtch. Current Dode current (ma) * see note below Curr max Voltage Current lmt (ma) ( ) sgn ndcates lmt rather than actual current Dode voltage (V) Temp set Temperature set pont ( C) Temperature Actual temperature ( C) TEC current TEC voltage Frequency Current to thermoelectrc (Pelter) cooler (A) Voltage on thermoelectrc (Pelter) cooler (V) Frequency actuator offset, usually slow pezo (normalsed to a range of ±1) Note The current dsplay shows the current set pont, not the actual dode current. If BIAS s enabled, then durng the scan the actual dode current wll be hgher or lower than that shown, dependng on the adjusted value of the BIAS trmpot. The current lmt crcut prevents the actual dode current from exceedng the lmt set by I max (see page 13), even f the current settng plus current modulaton (nternal, external, or BIAS) would exceed I max. Use CHAN B Current to see the actual dode current, and the effect of BIAS and current lmt when scannng.

23 2.2 Front panel dsplay/montor 11 CHAN A Several mportant sgnals can also be montored externally wth an osclloscope va the rear connectors CHANNEL A, CHANNEL B and TRIG. The outputs to these can be selected wth the CHAN A and CHAN B selectors. Input Flter Photodetector [30 mv/µw] Fltered photodetector, 40 khz low pass Freq Frequency-scannng actuator (STACK) [1 V/48 V] Slow Slow feedback STACK [1 V/0.24 V] DISC [1 V/4.8 V] Fast Current feedback [1 V/100 µa] CHAN B Input Photodetector [30 mv/µw] Error Feedback error Current Dode current [10 V/A*] Mod Modulator output current [1 V/A] Temp Temperature error [10 V/ C] * Note: 5, 10, 12.5, 25 V/A for DLC102/202/252/502.

24 12 Chapter 2. Connectons and controls 2.3 Rear panel controls and connectons Dode Laser Controller EXT INPUTS CHANNEL A CHANNEL B ERROR / CURR MOD SWEEP / PZT MOD MOD OUT Interlock LASER TRIG Tgan Imax fsweep I mod Photodetector Model: Seral No: Made n Australa IEC power n/out Fan Interlock The unt should be preset for the approprate voltage for your country. Please contact MOGLabs for nstructons f you need to change the power supply voltage. The output IEC connector s a drect connecton to the nput power, after the nput mans flter. Ths outlet should be used only to power a montorng osclloscope. It s provded to mnmse ground-loop nose problems. The fan speed s temperature-controlled. The DLC wll not power on the laser unless the pns on ths connector are shorted. A standard 2.1 mm DC plug s provded. LASER Connecton to laser head. Ths connector provdes dode current, two pezo drves, temperature sense, and TEC current. A DVI-D Dual cable s provded. WARNING: The pezo drve sgnals can be lethal. The hgh-voltage outputs, dode current and TEC current wll be dsabled f the cable s dsconnected, or f the man or head nterlocks are open-crcut, but these protecton features should not be assumed. T gan Temperature control feedback gan. Increase ths f the response tme s too great or f the temperature error s large. Reduce ths f the temperature oscllates. CHANNEL A, B Montor outputs; connect to osclloscope, channels 1 and 2.

25 2.3 Rear panel controls and connectons 13 TRIG I max ERROR/CURR MOD SWEEP/PZT MOD Photodetector fsweep Osclloscope trgger, TTL-level. Connect to external trgger nput on osclloscope. Set osclloscope trggerng for external, rsng edge. Dode current lmt. The current lmt can be set wth the dsplay selector set to Curr max. See page 10 for further nformaton. Input for externally derved feedback error sgnal (DIP swtch 5) or for current modulaton (DIP swtch 6). Impedance 5 kω. Sgnal normally < ±1 V; max ±8 V. If used for external error, DIP swtch 5 ON, apples n lock mode only. If used for current modulaton, DIP swtch 6 ON, the senstvty s 2.5 ma per volt. Sgnal paths can be found n appendx H. Input for externally generated frequency control (STACK, DIP swtch 9 and/or DIP swtch 13) or for pezo DISC modulaton (DIP swtch 14). Ths sgnal s added to the nternal error sgnal f DIP swtch 15 s on. If DIP swtch 9 s on, the nternal sweep ramp s replaced wth the external sweep nput. In that case, the external sweep sgnal should be 0 to 2.5 V and must cross 1.25 V to generate trggerng for the osclloscope (TRIG) and lockng. Impedance 5 kω. Senstvty 48 V per volt (120 V max). If the external sweep s less than 0 to 2.5 V then the current bas di/df wll be reduced n proporton. It s possble to add the SWEEP sgnal to the nternally generated STACK sgnal n all crcumstances, for example to test actuator response whle locked to a transton. To do ths, add a resstor (approxmately 5k0, sze 0603) at R113. Sgnal paths can be found n appendx H. Connecton to photodetector unt. A standard 6-pn FreWre (IEEE- 1394) cable s provded. Scan rate, 4 70 Hz. Note that the rapd return of the STACK sweep drve can excte mechancal oscllatons n the laser. Slower sweeps

26 14 Chapter 2. Connectons and controls are recommended; usually 10 or 20 Hz works well but f rngng s observed at the start of the sweep, reduce fsweep. MOD OUT Connecton to external modulator, output s 0 to ±500 ma, ±8 V. Current sensng wth 1 Ω sense resstor. It can be drectly connected to a 50 Ω load, gvng a voltage of ±5 V f I set s adjusted to ±100 ma. See appendces D, E. I mod Modulaton depth: the range of current modulaton on MOD OUT and f DIP swtch 3 s on, the dode current.

27 2.4 Internal swtches and adjustments Internal swtches and adjustments See appendx H for schematc overvews of the pezo and dode current control sgnals, and the effect of the dfferent DIP swtches. See appendx J for the locaton of relevant nternal components. CAUTION The cover of the controller should be left on, even loosely, to ensure proper arflow and coolng. Interlock Lnk LK1 (rear rght of man board) can be shorted nternally to avod the requrement for an external nterlock, f permtted by local safety regulatons. 120 V Lnk LK2 (near LK1 and 160 V test pont) can be shorted to lmt the pezo stack voltage to 120 V, or removed to ncrease t to 150 V. DIP swtches OFF ON 1 DISC fxed DISC ON 2 STACK fxed STACK ON 3 Current dther OFF Current dther ON 4 Current bas OFF Current bas ON 5 Internal error External error 6 External current mod OFF External current mod ON 7 AC lock DC lock 8 Sngle photodode Dual photodode 9 Internal sweep External sweep 10 STACK feedback STACK feedback + 11 STACK sweep + STACK sweep 12 AC current feedback DC current feedback 13 STACK nternal STACK external 14 DISC nternal DISC external 15 Default External slow error 16 Current mod by SLOW control sgnal (for DBR/DFB)

28 16 Chapter 2. Connectons and controls DIP 1, 2 DIP 3 Cauton DIP 4 DIP 5 DIP 6 Please refer to secton 2.5 below for dscusson of feedback confguratons. Wth DIP 3 ON, the 250 khz modulator drectly modulates the njecton current to cause frequency modulaton of the laser frequency. In conjuncton wth a frequency-dependent absorpton on the photodetector sgnal, for example wth an atomc vapour cell or etalon (see secton 3.5). The modulaton depth s adjusted va nternal trmpot RT6 and the I mod rear-panel trmpot. The modulaton can be swtched on and off va the front panel toggle swtch OFF/MOD. Current dther (DIP 3 ON) nherently ncreases the effectve lnewdth of the laser. The modulaton depth should be adjusted to the mnmum whch stll provdes a useful lockng sgnal. Enables njecton current bas, sometmes called feed-forward. If ths swtch n ON, the njecton current wll be modulated n conjuncton wth changes to STACK, for example as the laser frequency s ramped, or due to frequency feedback lockng. The depth of bas modulaton s controlled wth the BIAS front-panel trmpot. Approprate adjustment can substantally extend the mode-hop-free scan range of the laser. Externally derved lockng sgnals can be used to control the laser current and pezo actuators. If DIP 5 s ON, the nternally generated error sgnal s replaced wth the sgnal from the rear-panel ERROR nput, and then drves all feedback channels. The master gan adjustment, and both slow and fast gan adjustments, can be used. If ths swtch s ON, the rear-panel ERROR/CURR MOD sgnal s added to other current feedback sgnals, and the gan of the combned sgnal s enhanced by a factor of 25. All nternal servo shapng flters are bypassed by the external current modulaton. The gan knobs affect the nternally-generated error sgnals as usual. The FAST gan knob and +/ also affect the external current modulaton. The state of DIP 5 does not affect ERROR.

29 2.4 Internal swtches and adjustments 17 DIP 6 and DIP 12 DIP 7 DIP 8 DIP 9, 13, 14, 15 DIP 9 DIP 10, 11 If both DIP 6,12 are on, nternal slow feedback to STACK, and external current modulaton to the dode current, are enabled. Swtch 7 determnes whether AC (centre or top of peak) or DC (sde of peak) lockng s used. Generally AC s preferred because the nose at the modulaton frequency of 250 khz s much lower than at DC; thus AC lockng s largely free of slow drfts. However, for many applcatons a DC reference s perfectly adequate and allows lockng wth wder bandwdth. It can be convenent to subtract a background from the nput sgnal, for example to remove a Doppler background from a saturated absorpton reference. Swtch 8 swtches the photodetector to dfferental mode. The dfference between the two photodode sgnals s generated n the photodetector tself. These swtches determne the functon of the SWEEP nput, for example to provde an external frequency ramp, or to use an external lockng crcut (see secton 3.7) or to allow measurement of the actuator response functons. Wth DIP 9 ON, the laser frequency sweep wll be drven from an external ramp. Note that the sweep, suppled va SWEEP, should be 0 to 2.5 V and must cross 1.25 V to generate trggerng for the osclloscope and lockng. The TRIG sgnal wll output at 1.25 V. The front-panel SPAN knob controls the ampltude. The sgn of the response of the two pezo actuators can be reversed wth swtches 10, 11. For example, ncreasng the potental on STACK may ncrease or decrease the cavty length, whle DISC may act n the same or the opposte sense. It s mportant for lockng that both operate n the same sense. Also, t may be useful to reverse the scan for some applcatons. To reverse the sgn of DISC, reverse the error sgnal frst, and then adjust the sgn of the STACK and current feedback. Note The feedback to the STACK actuator reverses wth DIP 1 and so DIP 10 should also be flpped when DIP 1 s flpped, or the PHASE adjusted to

30 18 Chapter 2. Connectons and controls reverse the error sgnal. See secton 2.5 below for further dscusson. DIP 12 DIP 13 DIP 14 DIP 15 DIP 12, 16 Current feedback s normally AC coupled because slow feedback to STACK takes care of slow drfts. For lasers wthout pezo control, such as DBR and DFB dodes, DC feedback to current can be enabled by swtchng DIP 12 on. Wth external current modulaton (see DIP 6 above), DIP 12 on enables slow pezo feedback and AC coupled external current modulaton. If DIP 13 s on, the nternally generated STACK sgnal s replaced wth the external SWEEP sgnal, ndependent of the state of SCAN/LOCK. The change occurs after the offset (FREQUENCY) and STACK polarty (DIP swtch 11), before the SLOW gan adjust. It s possble to add the SWEEP sgnal to the nternally generated STACK sgnal n all crcumstances, for example to test actuator response whle locked to a transton. To do ths, add a resstor (approxmately 5k0, sze 0603) at R113. If DIP 14 s on, the nternally generated DISC sgnal s replaced wth the external SWEEP sgnal, ndependent of the state of SCAN/LOCK. To measure an actuator response, connect an external varablefrequency oscllator to the SWEEP nput, and sweep through the frequency range of nterest. Measure the laser frequency modulaton ampltude from the transmtted ntensty at the sde of a Fabry- Perot frnge or saturated absorpton transmsson peak (e.g. fg. 1.4), preferably wth a lockn amplfer. If DIP 15 s on, the external SWEEP nput replaces the normal nternallygenerated slow (pezo) feedback error sgnal. The change occurs before the SLOW gan adjust. The fast (current) feedback s unaltered, except for the sgnal actvated by DIP 16; see secton 2.5 below. Sweep, offset (FREQUENCY) and stack polarty (DIP swtch 11) are unaffected. Swtches 4, 12, 16 allow operaton of DFB/DBR lasers wthout external cavty feedback and thus wth only current as an actuator. Please refer to secton 2.5 below for dscusson of feedback confguratons.

31 2.4 Internal swtches and adjustments 19 Use swtch DIP 4 (current feed-forward bas) to drve the current wth the scannng ramp. Swtch DIP 16 adds the fast DISC sgnal to the current. DIP 16 and DIP 4 can be actve smultaneously. Swtch 12 enables DC couplng of the current feedback, rather than the default AC couplng, to allow current-only feedback lockng.

32 20 Chapter 2. Connectons and controls 2.5 Feedback confguratons The DLC s desgned to drve up to three feedback actuators wth approprate frequency bandwdths for each. The actuators are STACK, DISC and CURRENT. Sutable lasers nclude the MOGLabs ECDL whch has CURRENT and STACK feedback but no DISC pezo; DFB/DBR lasers whch only offer CURRENT feedback; and lasers wth all three. The nomnal feedback bandwdths descrbed below are defned by the unt gan bandwdth when all controls (MASTER, SLOW, FAST) are at ther centre postons. The actual closed-loop unty gan frequences wll depend on the partcular laser, dode, and pezos used and on the reference sgnal, so the frequences are only a gude. For CURRENT feedback, phase lead adjust can ncrease the bandwdth to 40 khz. Summary of confguratons DIP Descrpton A OFF OFF ON ON STACK slow DISC fast B ON ON ON ON STACK slow DISC fast C OFF ON ON OFF STACK fast DISC fxed D OFF OFF OFF ON STACK fxed DISC fast E ON X OFF OFF STACK fxed DISC fast For the MOGLabs ECDL, use opton C (default) or, to ncrease the range for slow drft, opton B. The confguratons above assume that ncreasng the voltage on STACK ncreases the laser frequency (by reducng the cavty length). Reverse DIP 10 f the opposte s true.

33 2.5 Feedback confguratons 21 A: STACK slow, DISC fast STACK: 20 db/decade, BW 50 Hz DISC: 40 db/decade, BW 1.5 khz CURRENT: 20 db/decade, BW 15 khz B: STACK slow, DISC fast, extra CURRENT STACK: 20 db/decade, BW 50 Hz DISC: 40 db/decade, BW 1.5 khz CURRENT: 20 db/decade BW 15 khz + flat response Addtonal CURRENT feedback wth flat response (no ntegrator) to boost low-frequency feedback. The combned current feedback gan s reduced 25. In ths confguraton, the error sgnal must be reversed; that s, the error sgnal should have a negatve slope at the lock pont, the +/- current feedback polarty toggle swtch should be down ( ). Note DIP 10 s ON. C: STACK fast, DISC fxed STACK: 40 db/decade, BW 750 Hz DISC: fxed CURRENT: 20 db/decade, BW 15 khz Hgh gan (fast) output to STACK reduces range of STACK to ±1 GHz before nternal sgnal saturates. D: STACK fxed, DISC fast STACK: fxed DISC: 40 db/decade, BW 1.5 khz CURRENT: 20 db/decade, BW 15 khz

34 22 Chapter 2. Connectons and controls E: CURRENT only STACK: fxed DISC: fxed CURRENT: flat, BW 15 khz DIP 12 should be ON for DC CURRENT feedback. DIP 4 ON to drve the current wth the scannng ramp. For DBR and DFB lasers and ECDLs when t s desrable to operate wthout pezo actuators.

35 2.6 Dgtal control Dgtal control HD12 s a 10-pn header whch provdes access to several control sgnals for lockng and for sample-and-hold of the lock-pont. HD12 s located near the DIP swtches, slghtly towards the front and lefthand sde of the unt (see appendx J). The pnout of the header s descrbed n secton I.4. The sgnals are standard TTL-compatble, > 2.4 V HIGH and < 0.8 V LOW. The nputs are ORed wth the front toggle swtches, such that the sgnal s actvated f ether the dgtal nput s actve (.e. HIGH) or the toggle swtch s on (down). Laser ON LOCK FAST HOLD HIGH to swtch the laser dode current on, regardless of the state of the front-panel swtch. HIGH to SLOW lock, regardless of the state of the front-panel swtch. LOW to sweep, f the front-panel swtch s up. HIGH to FAST lock. HIGH to freeze STACK. Wth HOLD actve, the feedback to the slow pezo wll be fxed by a sample-and-hold crcut. The dode current can then be modulated va the rear-panel CURR MOD nput (wth DIP swtch 6 ON), to jump the laser frequency quckly, wthout the error feedback crcut competng wth the external modulaton. External current modulaton s ndependent of the FAST lock status. FAST lock s asynchronous wth HOLD actve; that s, the FAST lock wll actvate mmedately, rather than the normal delay untl the scan ramp reaches the sweep centre. To relock, restore the CURR MOD nput voltage, and return the HOLD nput LOW; the lockng feedback wll then be reactvated. FAST lock can then be reactvated. Ths ablty can be used for auto-lockng under computer control, and also for atom trappng experments nvolvng sequences wth dfferent detunngs for polarsaton gradent coolng and for compresson.

36 24 Chapter 2. Connectons and controls 2.7 Internal trmpots RT6 RT12 RT13 RT15 Current dther ampltude lmt Phase lead Ambent temp for actve sensors (AD590, AD592) TEC current lmt RT6 RT12 RT13 For AC lockng, ether the laser frequency or the external reference must be modulated at the DLC dther frequency, 250 khz. An external modulator (see appendx E) s normally used, but the laser njecton current can be modulated drectly. The modulaton depth s then controlled by the rear-panel I mod trmpot. The lmt to the current modulaton s factory set va RT6. A phase-lead crcut s ncluded on the current feedback channel, to boost the output at hgher frequences (tens of khz). RT12 controls the phase lead and can be adjusted for dfferent dodes; see appendx 4. Offset adjustment for actve temperature sensors (AD590, AD592), so that temperature reads n C. RT15 Current lmt for TEC output. To set, change the set temperature suddenly, and adjust RT15 whle readng the TEC current.

37 3. Operaton 3.1 Smplest confguraton In the smplest applcaton, the MOGLabs DLC wll be used to control just the dode njecton current and temperature. All connectons are va a sngle cable to the MOGLabs laser. If usng wth a non- MOGLabs laser, please see appendx G for nformaton on connectng the dode, thermoelectrc Pelter cooler (TEC), and temperature sensor va the laser head nterface board. For operaton wth DBR/DFB dodes, please see appendx C. To operate n passve confguraton: 1. Ensure the power s on, and the STANDBY/RUN swtch s on STANDBY. In ths mode, most crcuts wll be swtched off, ncludng much of the man nternal board, low and hgh voltage DC supples, photodetector, pezo and dode outputs. On frst power-up, the STANDBY ndcator wll be red; ths s normal. The swtch should be set to RUN to ntate temperature control, and then may be returned to STANDBY. 2. Swtch from STANDBY to RUN. The ndcator should change from red (f just powered up), or orange, to green. If the ndcator s not green, the TEC or sensor s not correctly wred. In RUN mode, all electroncs wll be powered up, except for the dode njecton current supply and pezo drvers. 3. If the controller s swtched back to STANDBY, all electroncs wll be powered down, except for the temperature controller, whch wll contnue to operate normally. 4. Adjust the temperature setpont: frst select Temp set on the dsplay selector, then adjust T set va the front-panel trmpot. 5. Temperature control can be optmsed by adjustment of the ntegrator gan, rear-panel trmpot T gan. Adjust to mnmse 25

38 26 Chapter 3. Operaton the tme to equlbrate the temperature (CHANNEL B output, front panel CHAN B set to Temp) after a sudden change n T set. 6. Adjust the current control knob to mnmum (fully ant-clockwse). 7. Set the dode maxmum current: select Curr max on the dsplay selector, then adjust the maxmum allowed dode njecton current va the rear panel I gan trmpot. Note that wth the dsplay set to Curr max, a negatve sgn ( ) provdes a vsual remnder that the lmt s beng dsplayed rather than the actual current. 8. Swtch the laser on. The ndcator on the laser head board should llumnate, and the front-panel ndcator above the swtch should turn green. Note that the SCAN/LOCK and fast-channel OFF/LOCK swtches must be set to SCAN and OFF respectvely. Other protecton features wll prevent current to the dode, ncludng man cable dsconnect, and open crcut on the rear-panel or laser head nterlocks. 3.2 Laser frequency control In normal (SCAN) mode, a sawtooth ramp s suppled to the the stack, at frequency of fsweep = 4 to 70 Hz; see fg Dependng on the frequency offset (FREQUENCY) and the wdth of the scan (SPAN), the STACK can saturate ether at the low or hgh frequency end of the sweep. The spectrum may then be constant, although f current bas s enabled the laser frequency may stll scan n that range, but at a smaller slope (see secton A.2 for detals). 120V STACK FREQUENCY SPAN 0V 5V 0V TRIG tme Fgure 3.1: Stack output voltage and trgger sgnal, when scannng.

39 3.3 External scan control 27 Several adjustments of the frequency sweep are possble: SCAN/LOCK FREQUENCY The SCAN/LOCK swtch should be on SCAN. Offset;.e. md-pont voltage of the ramp. SPAN Sets the heght of the ramp; see fg BIAS fsweep The BIAS front-panel trmpot controls the feedforward bas njecton current whch follows the ramp, to enable wder mode-hop-free scans. The bas can be adjusted n a tral-and-error manner to acheve the wdest possble scans. BIAS s dsabled unless nternal DIP swtch 4 s ON. The rear-panel fsweeptrmpot adjusts the ramp rate from 4 to 70 Hz. Note The rapd return of the STACK sweep drve can excte mechancal oscllatons n the laser. Slower sweeps are recommended; usually 20 Hz works well but f rngng s observed at the start of the sweep, reduce fsweep. Fgure 3.2 s an example of an absorpton spectrum acqured wth the smple scannng confguraton, usng a standard (uncoated) dode and BIAS current feed-forward. The transmsson of the laser through a rubdum vapour cell was detected on the DLC photodetector, as the laser frequency was scanned through the 5 2 S 1/2 5 2 P 3/2 levels. 3.3 External scan control An external source can be used to control the laser frequency whle n SCAN mode. 1. Connect the external frequency control (ramp, or DC) sgnal to the rear-panel SWEEP external nput. 2. Select external sgnal by settng DIP swtch 9 to ON. 3. Set DIP swtch 4 on f current bas s requred.

40 28 Chapter 3. Operaton Saturated absorpton spectrum for natural Rb 0.8 Intensty Rb 87 F=2 Rb 85 F=3 Rb 85 F=2 Rb 87 F= Frequency (GHz) Fgure 3.2: A saturated absorpton spectrum of rubdum usng a standard uncoated laser dode and low dffracton effcency gratng n Lttrow confguraton (upper trace). The lower trace shows the AC-modulaton error sgnal (see 3.5). 4. Toggle DIP swtch 11 (external sweep has reverse polarty to nternal). 5. Set SCAN/LOCK to SCAN. The front-panel SPAN knob controls the ampltude. Note The frequency control suppled to SWEEP should be between 0 and 2.5 V and must cross 1.25 V to generate essental nternal trggerng. The TRIG sgnal wll output at 1.25 V. 3.4 Lockng to an atomc transton: DC Fgure 3.3 shows how an ECDL can be locked to an atomc transton as determned from absorpton n a vapour cell. The basc confguraton descrbed n 3.2 s extended wth the DLC photodetector, and an atomc vapour absorpton cell. A Fabry-Perot optcal cavty or other frequency reference could also be used. The photodetector can be used n sngle channel mode (default) or wth balanced dfferental nputs, for example to subtract a Doppler

41 3.4 Lockng to an atomc transton: DC 29 M M BS λ/4 λ/4 Vapour cell BS PD BS ECDL Servo Offsets Fgure 3.3: Schematc setup for DC lockng to an atomc transton. PD s the DLC photodetector. BS beamspltter, M mrror, λ/4 retarder. background from a saturated absorpton spectrum. Sample osclloscope traces obtaned n DC lockng ( sde of frnge ) mode are shown below, for wde and narrow spans. These traces were obtaned wth an 8 cm long Rb vapour cell at room temperature. C1 C1 C2 C2 Ch1 100mV Ch2 100mV 20.0ms Ch1 100mV Ch2 100mV 20.0ms Fgure 3.4: Examples of spectra for DC lockng, for wde and narrow spans (upper traces) and error sgnals (lower traces). To operate n DC lockng confguraton: 1. Select DC lockng by settng nternal DIP swtch 7 to ON. 2. If usng dfferental nputs, set nternal DIP swtch 8 to ON. 3. Usng an optcal beamspltter, a stray reflecton, or by other

42 30 Chapter 3. Operaton means, deflect a fracton of the laser output through the vapour cell. The MOGLabs DLC s desgned to operate best wth about 250 µw ncdent on each of the S-PIN photododes. Lensed and fltered photododes are standard, to mnmse the nfluence of background lght, but best results wll be obtaned f lght from ncandescent or fluorescent lamps s elmnated. 4. If usng balanced nputs, the second lght beam should llumnate the second photodode. 5. Fnd an approprate spectral feature. 6. Adjust front-panel INPUT OFFSET and ERROR OFFSET to obtan a zero-crossng ERROR sgnal at the desred frequency. The slope should normally be negatve (dependng on DIP swtches 10, 11). The ERROR sgnal can be nverted by coarsely adjustng the PHASE control. 7. Set SLOW and FAST gans to mnmum (fully ant-clockwse). 8. Swtch SCAN/LOCK to LOCK. 9. Swtch OFF/LOCK to LOCK. It may be necessary to nvert the sgn of the fast lock wth the ± swtch. 10. Increase SLOW and FAST gans to mnmse the error sgnal, deally usng an external audo spectrum analyser. The gans should be ncreased untl the onset of oscllaton, and then reduced. See chapter 4 for addtonal dscusson of feedback optmsaton. Note that t s not necessary to zoom n on the desred lock pont. The controller wll automatcally lock to the zero-crossng closest to the trgger pont,.e. to the centre of the osclloscope trace. When the laser s locked (step 8 above), the photodetector (INPUT) sgnal should be fxed at the value correspondng to the lock frequency n ths case zero snce for DC lockng, the controller locks to the zero-crossng.

43 3.5 Lockng to an atomc transton: AC Lockng to an atomc transton: AC Fgures 3.5 and 3.6 show two alternate saturated absorpton spectroscopy arrangements, useful for AC ( top of frnge ) lockng. The laser frequency can be drectly modulated va the dode current (see 2.4, DIP swtch 3), or usng an external modulator. The controller ncludes a modulator drver wth suffcent power to drve a col drectly for Zeeman modulaton, or an external modulator such as an acousto-optc modulator can be used; see appendx D. Sample osclloscope traces obtaned n AC lockng mode are shown below, for wde and narrow spans. These traces were obtaned wth an 8 cm long Rb vapour cell at room temperature, usng a Zeeman modulaton col as descrbed n appendx D. To operate n AC lockng confguraton: 1. Select AC lockng by settng nternal DIP swtch 7 to OFF. 2. Connect the photodetector module and optmse the photosg- M M BS Vapour cell + col λ/4 λ/4 AOM BS PD f ~ 150mm f ~ 25mm 250kHz BS ECDL Servo Lock-n Fgure 3.5: Schematc setup for AC lockng to an atomc transton. PD s the DLC photodetector. BS beamspltter, M mrror, λ/4 retarder. Beam expandng lenses ncrease sgnal power wthout power broadenng.

44 32 Chapter 3. Operaton nal on CHANNEL A. The MOGLabs DLC s desgned to operate best wth about 250 µw ncdent on the S-PIN photodode. Lensed and fltered photododes are standard, to remove most background lght, and when AC lockng at 250 khz modulaton frequency, any remanng photocurrent from background lghtng should not be a problem. 3. Adjust the INPUT OFFSET such that saturated absorpton trace s near zero. 4. Swtch the modulaton on wth OFF/MOD. 5. Fnd an approprate spectral peak and observe the dspersve error sgnal wth CHAN B set to ERROR. 6. Optmse the error sgnal (usually for maxmum slope) by adjustng the front panel PHASE. The error sgnal slope should normally be negatve (dependng on DIP swtches 10, 11) at the desred frequency. 7. Adjust the GAIN such that the error peaks are roughly mv peak-to-peak. Note that larger sgnals are not recom- PD PBS λ/4 Vapour cell + col M f ~ 25mm f ~ 150mm λ/2 250kHz ECDL Servo Lock-n PBS Optcal solator Fgure 3.6: Schematc setup for a more compact and more easly algned saturated absorpton arrangement. PD s the DLC photodetector. PBS polarsng beamspltter, M mrror, λ/4 and λ/2 retarders. Beam expandng lenses ncrease the sgnal power whle mnmsng saturaton broadenng.

45 3.5 Lockng to an atomc transton: AC 33 C1 C1 C2 C2 Ch1 100m V Ch2 100m V 20.0m s Ch1 100m V Ch2 100m V 20.0ms Fgure 3.7: Examples of spectra for AC lockng, for wde and narrow spans (upper traces), wth error sgnals (lower traces). mended; although the sgnal-to-nose may look better on an osclloscope, that s a reflecton of the nose of the osclloscope and s not the case nsde the DLC controller. 8. Adjust front-panel ERROR OFFSET such that the error sgnal s crossng zero at the desred frequency. 9. Set SLOW and FAST gans to mnmum (fully ant-clockwse). 10. Swtch SCAN/LOCK to LOCK. 11. Swtch OFF/LOCK to LOCK. It may be necessary to nvert the sgn of the fast lock wth the ± swtch. 12. Increase SLOW and FAST gans to mnmse the error sgnal, deally usng an external audo spectrum analyser (see chapter 4). The gans should be ncreased untl the onset of oscllaton, and then reduced. See chapter 4 for addtonal dscusson. Note agan that t s not necessary to zoom n on the desred lock pont. The controller wll automatcally lock to the zero-crossng of the error sgnal (n ths case the peak of a spectral feature) closest to the trgger pont, at the centre of the osclloscope trace. When the laser s locked (step 10 above), the photodetector (INPUT) sgnal should be fxed at the value correspondng to the lock frequency. In contrast to the DC lockng case, ths should be the INPUT sgnal at the peak of the spectral feature, not zero.

46 34 Chapter 3. Operaton 3.6 External sweep An external ramp can be used to control the frequency sweep, for example f very slow sweeps are requred, or for computer-controlled sweeps. To operate wth external sweep: 1. The external sweep sgnal MUST have 1.25 V offset. That s, t must transton through 1.25 V at some tme durng the sweep. 2. The external sweep sgnal should be wthn 0 to 2.5 V range. 3. Connect the external sweep sgnal to the rear-panel SWEEP external nput. 4. Select the external sweep sgnal by settng nternal DIP swtch 9 to ON. 5. Normally DIP swtch 4 should be on so that current bas (feedforward) s enabled. 6. The front panel knobs FREQUENCY and SPAN wll stll work. Set FREQUENCY to ts mdpont (0 V on the front-panel dsplay, wth Frequency selected). Set SPAN to fully clockwse. You can then change your external sweep DC offset and peak-to-peak ampltude, and/or use FREQUENCY and SPAN to control the offset and sweep ampltude. Note: f you have a Rev. 8 controller, you wll probably need to remove resstor R113. Contact MOGLabs for assstance. 3.7 Lockng usng an external sgnal The MOGLabs DLC can be used wth a wde varety of externally generated dspersve sgnals; see appendx E for examples, and appendx H for block dagrams of the control crcutry. Note that ths secton refers to error and control sgnals. An error sgnal s a dspersve sgnal wth a potental that depends on laser frequency. A control sgnal s a feedback servo sgnal generated from

47 3.7 Lockng usng an external sgnal 35 an error sgnal, usually wth PID (proportonal-ntegral-dfferental) or PIID (PID wth a double ntegrator) response. When usng an external error or control sgnal, t wll normally be advsable to swtch off the modulator (DIP swtch 3) External error sgnal To operate wth externally generated error sgnal, but usng the nternal DLC servo PIID feedback control: 1. Connect the external error sgnal to the rear-panel ERROR external nput. 2. Select the external lockng sgnal by settng nternal DIP swtch 5 to ON. DIP swtch 6 should be OFF. 3. Follow the procedure above for DC lockng. The bandwdth lmt wll be the same as for a DLC-generated error sgnal; that s, about 25 khz on the fast (current) channel External fast (current) control for hgher bandwdth For hgher bandwdth feedback, a fast control sgnal can be nput on ERROR and enabled va DIP swtch 6. The fast sgnal wll then control current drectly, wthout DLC feedback control. The external feedback crcut must nclude approprate response. If usng current-only control, wthout pezo control, then PID or PIID s probably approprate. If the DLC s stll controllng the pezo (wth SLOW lock turned on) then the current control should be AC coupled, and nclude gan reducton at hgh frequences to avod servo loop oscllaton External fast and slow To control both current (fast) and pezo (slow) wth external sgnals:

48 36 Chapter 3. Operaton 1. Connect fast control sgnal to ERROR. 2. Enable fast current control wth DIP swtch Connect slow error sgnal to SWEEP. 4. Enable slow pezo control wth DIP swtch 15. The pezo wll be controlled by the DLC f SCAN/LOCK s on SCAN, and by the external slow sgnal when swtched to LOCK. The slow sgnal should be a dspersve error sgnal wthout PID or other servo response functon. The fast sgnal should be AC coupled, and nclude gan reducton at hgh frequences to avod servo loop oscllaton. 3.8 External control of lock frequency setpont It s often useful to have external control of the lock frequency setpont, for example to suddenly change the detunng of a laser. See secton 2.6 for dscusson of such external control.

49 4. Optmsaton Laser frequency stablsaton s a complex and ongong research topc. A thorough treatment would requre extensve dscusson of control theory, actuator response, mechancal desgn, laser-atom nteractons and electroncs. Here we consder the problem from a pragmatc perspectve. The laser s assumed to be moderately stable, operatng close to the desred frequency, wth a lnewdth of a few MHz averaged over a typcal measurement tme of about one second. The very short-term lnewdth s determned by the Schawlow-Townes (S-T) lmt, whch s typcally less than 100 khz. The MOGLabs DLC wll stablse the laser frequency to an external reference, usually an atomc absorpton feature, and reduce the effectve lnewdth as close as possble to the S-T lmt. Achevng the best frequency lockng stablty requres careful optmsaton of the sgnal-to-nose rato (SNR) of the frequency dscrmnaton sgnal obtaned from the saturated absorpton or other reference. Then the phase and gan settngs must be optmsed, preferably by measurng the feedback error sgnal spectrum. 4.1 Frequency reference The frequency reference s crtcal to the performance of the MOGLabs DLC: the controller cannot reduce the laser frequency nose wthout an approprate frequency-dependent reference sgnal. The DLC has been desgned to work wth a saturated absorpton reference, as shown n fgures 3.5 and 3.7. Users should famlarse themselves wth saturated absorpton spectroscopy, for example as descrbed n Demtröder [5]. The frequency dscrmnator ( ERROR ) SNR should be optmsed to 37

50 38 Chapter 4. Optmsaton produce clear (low-nose) dspersve error sgnals as shown n the upper trace of fg Note that the error sgnal should be about 0.5 V p-p. Whle the sgnal looks cleaner at larger ampltude relatve to background osclloscope nose, n fact the overall performance wll deterorate. Other mportant factors to consder: Probe power The probe power should be about 250 µw. Hgher power wll ncrease the photosgnal, but the detector saturates at about 500 µw. Probe ntensty The probe ntensty should be low to reduce powerbroadenng. Thus, the probe beam should be expanded to 5 or 10 mm dameter, to allow hgh power and low ntensty, as dscussed n secton 3.5. Polarsaton The frequency dscrmnator (ERROR) sgnal s senstve to the pump and probe polarsatons. Good polarsers and careful algnment can be very helpful. Col desgn See appendx D. Sheldng The Zeeman col produces substantal magnetc felds, oscllatng at 250 khz. These felds can readly nduce problematc potentals and currents n the laser head and/or man crcut board. In partcular, t s qute possble to produce a larger frequency modulaton from nduced currents n the laser dode than from the Zeeman modulaton of the reference. It s vtal that the col be located far from the man unt and from the laser, or that t be shelded. A layer of hgh-permeablty materal (soft ron or mu-metal) s probably adequate. To test ths, smply reverse the polarty of the col connecton. If the error sgnal s also reversed, but otherwse smlar, then the sheldng s probably adequate.

51 4.2 Nose spectra 39 MOGLabs DLC ECD-003 monoblock laser nose spectra Frequency nose LSD [khz/rthz] Unlocked Pezo Pezo & current 0.01 Off resonance Frequency (Hz) Fgure 4.1: Error sgnal spectra, wth laser unlocked, locked wth SLOW (pezo) feedback only, and wth SLOW and FAST (pezo+current) feedback. The off-resonance spectrum provdes nformaton on the effectve nose floor. 4.2 Nose spectra The master, slow and fast gans can be set as descrbed n chapter 3, ncreasng them untl the onset of oscllaton, and then reducng slghtly. If possble, an audo frequency spectrum analyser can be used to provde better gudance. A generc computer sound card wth spectrum analyss software gves reasonable results up to 20 khz. A good sound card (24-bt 200 khz, e.g. Lynx L22 or E-Mu 1212m) provdes nose analyss up to 100 khz wth 140 db dynamc range, surpassng most standalone audo spectrum analysers, at very low cost. Connect the spectrum analyser to the CHANNEL B output, and set the CHAN B selector to ERROR. You should see curves smlar to those shown n fg The nose spectrum wth laser unlocked was obtaned n scan mode, but wth zero span, and the frequency carefully set to an atomc resonance (the hghest saturated absorpton dp n fg. 3.7). Smlarly for the Off resonance curve, but wth the laser tuned far away from all res-

52 40 Chapter 4. Optmsaton onances, outsde a Doppler absorpton peak. The Off resonance spectrum gves the frequency dscrmnator nose floor: t s meanngless to try to reduce the laser frequency nose below ths level. Wth SLOW feedback enabled, the nose for low Fourer frequences s drastcally reduced. A double-ntegrator s used for slow feedback, such that the suppresson s 40 db/decade. The SLOW gan adjusts the 0 db gan pont; n the fgure, ths reaches approxmately 5 khz. Hgher gans result n oscllaton at a frequency correspondng to a pole n the pezo actuator response (.e. a mechancal resonance). If confgured to work wth the stack actuator only (see 2.4), then the SLOW feedback wll suppress nose only to a few tens of Hz. FAST feedback adds an addtonal 20 db/decade suppresson, wth 0 db gan beyond 20 khz, even as hgh as 40 khz, dependng on the dode, optcal feedback, the frequency dscrmnator nose floor and other detals. Typcally we fnd that the laser dode tself has a 90 phase lag at 15 to 100 khz. Some compensaton for that phase lag s provded by a phase lead compensator (see RT12, page 24). Ideally, the SLOW and FAST gans should be adjusted to mnmse the ntegrated nose (the area under the error spectrum). The data n fg. 4.1 show a small Bode bump at around 30 khz, ndcatng excessve current gan, leavng the laser margnally stable. For lower FAST gan, the Bode bump wll be reduced, at the expense of reduced suppresson of the mechancal resonance nose peaks around 2 khz. The frequency dscrmnator SNR that s, the dfference between the Unlocked and the Off resonance spectra (n the data shown above, about 10 db for hgh frequences) s crtcal. Improvements to the reference, for example usng a Fabry-Perot etalon rather than saturated absorpton spectroscopy, can provde much greater SNR and correspondngly greater laser frequency nose suppresson. See E.2, page 62, for one approach.

53 A. Specfcatons Parameter Specfcaton Current regulator Output current Max dode voltage Dsplay resoluton Nose Stablty 0 to 100/200/250/500 ma 3.2 V at full current; 6 V at half current /HC models up to 6.5 V at full current ±0.01 ma < 10 na rms (10 Hz 1 MHz) Warmup tme: 15 mnutes CURR MOD 5 kω, ±8 V max, senstvty 100 µa/v, 1.5 MHz bandwdth RF modulaton BIAS SMA 50 Ω, 160 khz 2.5 GHz, see below ±25 ma over full sweep Temperature controller TEC current max ±2.5 A TEC voltage max ±9 V TEC power max 22 W Stablty ±5 mk/ C Sensor NTC 10 kω, AD590, AD592 Range 0 30 standard; extended range optonal Dsplay resoluton ±0.01 Note The TEC s controlled wth a lnear regulator, whch wll overheat f the current load s hgh and the TEC voltage s low. Choose a TEC wth resstance of 4 to 5 ohms to optmse power to the devce. 41

54 42 Appendx A. Specfcatons Parameter Specfcaton Pezos STACK DISC Scan rate 0 to 120 V for FREQUENCY (default) 0 to 150 V optonal (LK2 removed) 100 ± 16.4 V feedback 4 to 70 Hz Note Note The default maxmum pezo voltage s 120 V but can be ncreased to 150 V by removng jumper LK2; see page 15. The maxmum pezo drve current s 10 ma, whch lmts the scan rates for pezos wth hgh capactance. For exmaple, for a 250 nf pezo, the rate should not be greater than 25 Hz. Photodetector Photododes Couplng Dode separaton Bandwdth Dmensons S-PIN, IR fltered 740 nm 1100 nm, 1 1 mm 2 sensor, ±10 feld of vew See appendx F for spectral response. Optons: unfltered 400 nm 1100 nm ± 20, ±70 AC and DC, sngle or dfferental 10 mm 720 khz mm

55 43 Feedback system MOD OUT PHASE INPUT OFFSET ERROR OFFSET GAIN Bandwdth (gans at mdpont) 250 khz, ±8 V, ±500 ma Current output (1 Ω sense) Control va I set rear-panel trmpot 0 to 360 (mn) 10 V to +10 V ±0.5 V MASTER SLOW FAST SLOW FAST ±20 db MASTER ±20 db MASTER ±20 db 0 db at 700 Hz 0 db at 80 khz Protecton and status External nterlock Laser head enclosure nterlock Key swtch nterlock Delayed soft-start Open crcut detect Dode current lmt 2.1 mm DC power plug (provded) 2-pn MOLEX connector (provded) STANDBY/RUN 3 s delay + 3 s ramp Laser cable, TEC, temperature sensor Rear panel trmpot Imax

56 44 Appendx A. Specfcatons STANDBY/RUN LED STATUS LED DARK RED ORANGE GREEN RED ORANGE GREEN AC mans off, or fault condton detected (TEC falure, polarty reversed, open-crcut, cable unplugged, mssng sensor, temperature out of range) AC mans power on Standby (temperature controller on) Fully operatonal (pezo, current, ramp) Start sequence error or fault (Ether LOCK swtch ON, nterlock open, head cable dsconnected, temperature controller fault detected) Ready Dode runnng Mechancal & power Dsplay Fan IEC nput IEC output 4.5 dgt LED; standard colour red 12 V DC ball-bearng Temperature controlled 110 to 130 V 60Hz or 220 to 260 V 50Hz Fuse: 5x20mm, ant-surge (slo-blo) ceramc, 250V/2.5A Common ground wth power nput Intended for osclloscope; 1 A max Dmensons Standard 2U 19, WxHxD = mm Weght 4.3 kg (excludng cables, laser head board, photodetector). 8 kg shppng

57 A.1 RF response 45 A.1 RF response Ref -20 dbm -20 TG -30 dbm * Att 50 db * RBW 30 khz * VBW 10 MHz SWT 17 s Center 1.5 GHz 300 MHz/ Span 3 GHz Fgure A.1: RF response, SMA nput on laser headboard to dode SMA output. A.2 Sweep saturaton and trgger In normal scannng mode, a sawtooth s suppled to the stack pezo (or other laser frequency actuator), at a frequency of 1 to 70 Hz; see fg. A.2. At the nomnal mdpont of the sweep, a trgger (low to hgh) sgnal s output va the rear panel TRIG connecton, for synchronsng to an osclloscope or external experment. The span may be lmted by the mnmum and maxmum voltage that can be appled to the actuator, 0 and 120 V [150 V optonal]. That s, the ramp may saturate, as shown n fg. A.2. The perod remans fxed, and the trgger remans at the centre of the perod, but the laser frequency wll not scan for the entre perod. Thus the spectrum wll appear to shft to the left or rght of centre and wll be flat for part of the span. For stuatons where complete lnear spectra are needed, the actual ramp output should be montored usng the Freq selecton of the CHAN A output.

58 46 Appendx A. Specfcatons 120V FREQUENCY 0V 5V 0V STACK TRIG SPAN tme Fgure A.2: STACK output voltage and trgger pulse, when FREQUENCY s set near the mdpont (upper) or moved closer to 0 V (lower), where the output voltage exceeds the maxmum range.

59 B. Troubleshootng The MOGLabs DLC detects a wde range of fault condtons and deactvates related crcutry accordngly. The front-panel LEDs provde ndcaton of the state of these functons. B.1 STANDBY/RUN ndcator Colour DARK Status Temperature controller off. Reset va keyswtch, RUN STANDBY RUN Possble faults: AC mans off Interlock(s) dsconnected TEC open or short-crcut TEC polarty reversed Cable dsconnected Temperature sensor dsconnected Actve temperature sensor connected to thermstor pns Thermstor connected to actve sensor pns Temperature out of range (< 5 C or > 35 C) External sweep selected (DIP swtch 9) but no external sweep suppled Wrong AC mans voltage RED ORANGE GREEN AC mans power falure (temperature controller off) Standby (temperature controller on) Fully operatonal (pezo, current, ramp) 47

60 48 Appendx B. Troubleshootng B.2 Dode OFF/ON ndcator Colour RED Status Fault Reset va OFF/ON swtch ON OFF ON Possble faults: SCAN/LOCK swtch not up (SCAN) OFF/LOCK swtch not up (OFF) Rear nterlock dsconnected Laser head nterlock dsconnected Laser head cable dsconnected TEC dsabled (temperature out of range) Any one of +5, ±10, ±12 V nternal supples below nomnal by more than 1 V External sweep selected (DIP swtch 9) but no external sweep suppled ORANGE GREEN Standby: above condtons satsfed, dode ready to start Dode fully operatonal, pezos actve If the ndcator remans ORANGE after swtchng the dode ON, check the possble faults lsted above, n partcular the lack of a clock sync provded from nternal or external sweep (see 2.4).

61 B khz modulaton 49 B khz modulaton The 250 khz sne-wave oscllator reles on crtcal non-lnear behavour of an electronc component. Due to component drft, the oscllator may cease, and the AC error sgnal s then lost. A few small adjustments of trmpots wll restore the oscllator. I mod RT1 RT2 C51 P3 C24 P5 R119 C53 C56 TO220_KIT C1 C2 K1 L4 U4 H1 C4 L7 R20 R19 L5 C16 R21 R23 R601 R22 U10 U9 U8 C19 C18 R35 R36 R37 R28 R42 R43 C28 Dst RT4 RT3 Freq U15 C27 U19 C214 R59 R68 P35 Amp R71 C30 C35 R58 R77 RT5 R72 R67 C34 R69 R76 R54 R66 C33 R75 R79 R63 C32 R65 R81 R85 R90 D4 R80 U26 U25 U24 C37 R88 R87 R102 U27 RT6 R101 R99 R111 R100 R92 C38 R91 R97 R93 R118 C39 R96 Amp-I R98 R110 C45 R109 RT8 R552 C40 L9 Amp-D R116 R120 R117 Y X P7 C48 U35 U34 C47 U36 U28 R129 R130 R137 C50 R136 R128 C55 R139 Fgure B.1: 250 khz oscllator trmpots and testponts. 1. Measure test pont P35 (wth a multmeter) and adjust RT5 (labelled Amp) for 1.15 volts. P35 s near RT5 Amp trmpot. 2. Probe U25, Pn14 (top pn on rght-hand sde of U25), and adjust RT4 Dst and RT3 Freq to obtan a 2.6 V peak-peak, 250 khz sne wave. RT4 s used to brng the oscllator to lfe, and adjust the voltage gan. RT3 s used to adjust the frequency, only. Adjust RT4 frst, and once the sne wave appears, adjust RT3 for 250 khz, then fnally adjust RT4 for

62 50 Appendx B. Troubleshootng the 2.6 V p-p. 3. Probe test pont P7 (near RT8 Amp-D and U28), and adjust RT8 to obtan a 1.0 V peak-peak sne wave. 4. Wth the rear-panel I mod trmpot set to maxmum (fully clockwse), probe test pont P36 (just to the rght of U59) and adjust RT6 Amp-D to obtan a 1.0 V peak-peak sne wave. 5. Fnally adjust I mod to the requred modulaton depth, typcally about half way (6 turns ant-clockwse).

63 B.4 Lockng 51 B.4 Lockng The MOGLabs controller provdes feedback va three channels each wth a complex servo loop functon. A few common problems are addressed here; for more dffcult problems, MOGLabs wll be happy to work wth you to fnd the best possble soluton. B.4.1 SLOW does not lock Try lockng wth STACK only, DISC only, or both (see DIP swtches 1,2). It can be very useful to watch the SLOW output (va CHAN A) when lockng. Try lockng wth FAST channel only. If FAST lockng works but not SLOW, then there s a gan or polarty problem, or a dsconnect on one of the slow actuators (STACK, DISC). STACK feedback has wrong polarty. See DIP swtch 10. Lock sgnal zero-crossng too far from trgger pont. Gan too hgh. Try smaller and smaller gan, but be careful to ensure that the lock error sgnal s crossng zero. Loop response too fast for actuator. The controller s normally shpped wth slow-channel response gan of 1 (0dB) around 700 Hz. Please contact the factory for nstructons on changng ths for slower actuators. B.4.2 SLOW locks only brefly Usually ths s because the STACK feedback has the wrong polarty. Agan, t can be very useful to watch the SLOW output (va CHAN A) when lockng. Try flppng DIP swtch 10. Ensure the laser frequency s scannng properly,.e. that the STACK s properly connected and workng.

64 52 Appendx B. Troubleshootng B.4.3 FAST does not lock FAST feedback has wrong polarty. Try reversng the polarty wth the front-panel swtch. If the laser frequency s close to a mode hop (.e. ntrnsc dode cavty resonance s half way between two external-cavty longtudnal modes), the current response can be opposte to normal. Try adjustng the dode current very slghtly. Lock sgnal zero-crossng too far from trgger pont. Gan too hgh. Try smaller and smaller gan, but be careful to ensure that the lock error sgnal s crossng zero. B.4.4 FAST locks only brefly The FAST channel s normally AC-coupled (see DIP swtch 12), wth a tme constant of 0.1 s. Thus wth FAST feedback only, the laser wll drft off resonance. Normally the SLOW channel s used to compensate for very slow drft, but the laser can be locked by current feedback only wth DIP swtch 10 ON. Wth DC current feedback, the feedback saturates at ±10 ma.

65 C. Usng DBR/DFB dodes DBR (Dstrbuted Bragg Reflector) and DFB (Dstrbuted Feed- Back) dodes offer a compact and robust alternatve to ECDLs. The lnewdth of DBR and DFB dodes s typcally 2 to 3 MHz, and they are very susceptble to external optcal feedback, necesstatng two or even three stages of Faraday solator to prevent frequency nstablty. Ther frequency of operaton s controlled by temperature and current only, and the DLC must be reconfgured for optmum use wthout the usual pezo actuator control. The ssues are dscussed below. C.1 Fne current control Wthout pezo control of frequency, very fnd control of the current s requred. The coarse CURRENT knob can be used to set the current to wthn a mllamp or two, and the FREQUENCY knob must then be used. The FREQUENCY knob s normally used to adjust the pezo actuator offset, but t also couples to the current va the current feed-forward (bas). The BIAS trmpot can be adjusted such that the FREQUENCY knob vares the current by up to ±25 ma. For fner control, the BIAS can be reduced arbtrarly, from fully ant-clockwse ( 25 ma range) to fully clockwse (+25 ma range). Note that DIP swtch 4 must be ON. C.2 DC current feedback For lockng, the current feedback s normally AC coupled because slow drfts are compensated by the STACK actuator. Change to DC current feedback by turnng DIP swtch 12 ON. 53

66 54 Appendx C. Usng DBR/DFB dodes C.3 Slow current feedback The feedback sgnal that normally drves the DISC actuator can be coupled to the current feedback, by turnng DIP swtch 16 ON. C.4 Lock saturaton Slow drft s normally compensated by the STACK actuator, and hence the DISC and current feedback sgnals only have small range, and wth DBR/DFB dodes ths s easly saturated. Use feedback confguraton B (see secton 2.5) to maxmse the lock range. Dp swtch 1 should be ON. C.5 Specal optons Modfcatons can be made to the controller, ncludng: 1. External control of temperature set-pont, for example to enable slow frequency scans va the dode temperature. 2. Very slow lockng feedback to the dode current. 3. Very slow lockng feedback to the temperature set-pont. Contact MOGLabs for detals.

67 D. Modulaton cols The MOGLabs DLC s desgned to lock to an atomc transton, partcularly usng AC lockng. The frequency of the laser lght can be modulated (e.g. usng nternal current modulaton or an external modulator), or the reference can be modulated. In the latter case, an atomc reference can be modulated at low cost usng a solenod col wrapped around an atomc vapour cell, as shown below. Fgure D.1: Vapour cell, Zeeman col, and prmary exctaton col, mounted on PCB (avalable from MOGLabs). D.1 Feld requrements Ideally the Zeeman dther col should produce a frequency shft of about half the peak wdth, typcally a few MHz. Atomc stretched state transtons wll be Zeeman shfted by µ B = e h 2m e = 1.4 MHz/Gauss (D.1.1) so we need felds of around one Gauss (10 4 Tesla). The magnetc feld nsde a long solenod s B = µ 0 n (D.1.2) 55

68 56 Appendx D. Modulaton cols where n s the number of turns per unt length and the current. For wre dameter 0.4 mm, n = 2500 m 1, and the current requrement s only 22 ma/mhz. D.2 Col mpedance However, drvng an oscllatng current through a col s problematc because the mpedance grows wth the frequency. The mpedance s gven by X L = ωl where ω s the radal frequency and L the nductance. The nductance for a long solenod s L = µ 0 n 2 Al (D.2.3) where A s the cross-secton area of the col (πr 2 for a crcular crosssecton) and l s the col length. In practce, the nductance wll be less (e.g. see Wheeler [9]): L Wheeler = N 2 r 2 228r + 254l (mh) (D.2.4) where N s the total number of turns, r s the col radus n metres, and l s the length n metres (l > 0.8r). We have found that for dmensons typcal of cols wound around vapour cells, these two formulae agree wthn a factor of two. Note that the nductance ncreases wth n 2 whereas the magnetc feld and hence modulaton depth grows wth n; thus for our purposes, we generally prefer small n and large currents. On the other hand, the drvng voltage requrement (the back emf ) s gven by ε = L d dt εmax = L 0 ω (D.2.5) for a snusodal current of ampltude 0. The requred output slew rate s dv /dt = L d2 dt 2 Max L 0 ω 2. (D.2.6)

69 D.3 Impedance matchng 57 The MOGLabs DLC operates at ω = 250 khz. For a cell of length 8 cm, 0.4 mm wre, and 20 ma, we fnd L Wheeler 650 µh, and εmax = 20 V, and the maxmum slew rate s 32 V/µs. The MOGLabs DLC does not have that drect output capablty. Reducng n helps: nductance, and thus ε and dv /dt fall wth n 2 whle the frequency modulaton depth falls wth n. Thus a col of about 40 turns (500 m 1 ) and current ampltude of 150 ma should result n a modulaton depth of 1.3 MHz. However, we prefer to use a two-col mpedance matchng arrangement to ncrease the modulaton depth at smaller currents. D.3 Impedance matchng The DLC can drve up to ±0.5 A and ±8 V, wth a slew rate of 6 V/µs. Ths can be mpedance-matched to a hgh current col usng a transformer, or qute effectvely by drectly wndng a prmary on the man Zeeman col, as shown n the photo above. For the man Zeeman col, 0.4 mm to 0.6 mm dameter wre wound around the vapour cell, about 120 to 200 turns, works well. The col s balanced for the standard modulaton frequency of ω = 250 khz usng a capactor. The col s excted nductvely by a prmary, about fve to ten turns, connected drectly to the DLC modulator output (see fgure). The cell, cols, and balancng capactor can be convenently mounted on a PCB, as shown n the mage above, avalable from MOGLabs. L C C Fgure D.2: Crcut dagram for Zeeman col and exctaton col. Typcally the prmary s 5 to 10 turns, and the secondary 120 to 200 turns. The capactor should be chosen such that the capactve mpedance

70 58 Appendx D. Modulaton cols equals the nductve mpedance. That s, ωl = 1 ωc C = 1 ω 2 L. Usng the long-solenod equaton for nductance, (D.3.7) C = 1 ω 2 µ 0 n 2 Al (D.3.8) although n practce we fnd that the nductance s about half the long-solenod predcton and hence the capactance should be doubled, typcally about 1 to 5 nf. Wth ths arrangement, energy s stored n the nductor-capactor tank, and the DLC need only drve a small current (e.g. 50 ma peak-to-peak) to compensate for losses. WARNING! The potental across the secondary Zeeman col can easly be hundreds of volts! Please ensure that your col and capactor do not have exposed connectons! Also be sure to use capactors wth adequate voltage ratng. D.4 Tunng To maxmse the current n the secondary, the capactor should be chosen to tune the crcut to the DLC modulaton frequency. A spectrum analyser wth trackng generator s partcularly helpful: connect the col to the TG output, and to the SA nput, and sweep through the resonance (see fgure). Alternately, drve the col wth a functon generator and measure the magnetc feld wth another ndependent col (e.g. 20 turns of fne wre on a 1 cm dameter former) connected to an osclloscope. Adjust the capactor by addng or removng small capactors n parallel, untl the detected feld s maxmum at 250 khz. Agan, be sure to use capactors wth suffcent voltage ratng. In some cases the Q of the crcut may be too hgh, such that a seres resstor of about 0.5 ohm can result n ncreased current at 250 khz, and reduced senstvty to frequency drfts.

71 D.5 Sheldng 59 Ref -26 dbm TG -30 dbm * Att 5 db * RBW 1 khz * VBW 30 khz SWT 2.5 s Marker 1 [T1 ] dbm khz Center 250 khz 50 khz/ Span 500 khz Fgure D.3: Col response acqured usng a spectrum analyser wth trackng generator. The response shows a strong resonance near 250 khz. D.5 Sheldng Large magnetc felds oscllatng at 250 khz can readly cause problematc electromagnetc nterference (EMI). Inducton n the laser head or the cable to the laser head can easly produce substantal dode current modulaton. The col (and vapour cell) should be located far from the laser and from the controller, or shelded wth soft ron or a hgh permeablty alloy such as mu-metal or Conetc. We fnd that a tube made from thn (0.25 mm) sheet mu-metal, about 50% longer than the cell and col, s adequate.

72 60 Appendx D. Modulaton cols

73 E. External modulators and njecton current modulaton The MOGLabs DLC s desgned for AC lockng a laser to an external reference such as an atomc resonance or an optcal cavty. In many cases t s convenent to use the nternal modulator drver, and Zeeman modulaton of an atomc transton, as descrbed n appendx D. Zeeman modulaton s not always possble (e.g. f the reference s an optcal cavty), or desrable (e.g. due to magnetc nterference). The MOGLabs DLC can dther the laser dode njecton current (DIP swtch 3), or drve an external modulator, such as an electro-optc modulator (EOM) or acousto-optc modulator (AOM). E.1 Couplng crcut The DLC provdes a current-controlled modulaton output, wth 1 Ω sense resstor. It can be drectly connected to a 50 Ω load, producng a voltage of ±5 V wth I set adjusted to ±100 ma. Impedance-matchng and a DC level shft may be needed to drve an external modulator, as n the schematc below, desgned for the D323B RF amplfer from ISOMET. Fgure E.1: Couplng from MOD OUT to an external modulator. The ISOMET D323B RF drver has a frequency control nput wth 4 to 17 V range. We AC couple usng a smple 10T:10T ferrte bead trans- 61

74 62 Appendx E. External modulators and njecton current modulaton former. Prmary and secondary were wound wth 10 turns of PVCnsulated hookup wre around a ferrte bead approxmately 15 mm dameter. A 500 Ω potentometer allows control of the modulaton ampltude, and a 9 V battery and 100 kω potentometer provde a DC shft to set the centre modulator frequency. The latter allows frequency offset control of the modulated lght beam. E.2 Injecton current modulaton The MOGLabs DLC can dther the laser dode njecton current (set by DIP swtch 3), at the standard 250 khz, or wth hgh frequency modulaton (e.g. 10 MHz) va the SMA RF nput on the laser headboard. Very narrow lnewdths can be acheved wth sutably hgh bandwdth frequency dscrmnaton, for example by phase lockng two lasers. The dagram below shows an arrangement to lock two lasers to an EIT (electromagnetcally nduced transparency) resonance, whch obtaned a beatnote lnewdth below 1 khz [10]. Phase shfter 10MHz + Iac Saturated absorpton spectroscopy Mxer Lowpass 2.5MHz Phase lead X Probe laser Couplng laser Amplfer Error sgnal µ-metal Fber PBS λ/2 Rb vapor cell Photodode Photodode Mcrowave beatnote Fgure E.2: Hgh bandwdth lockng based on FM sdeband demodulaton [11, 6]. The probe laser s locked wth hgh bandwdth, relatve to the couplng laser, usng electromagnetcally nduced transparency as a dspersve reference.

75 E.2 Injecton current modulaton 63 The couplng laser was locked to the 5 2 S 1/2 F = P 3/2 F = 2 transton of 87 Rb usng the Zeeman modulaton technque, as n secton 3.5. The probe laser was tuned to the F = 1 F = 2 transton and modulated at 10 MHz. The two lasers copropagated through a Rb vapour cell and onto a photodode. An electromagnetcally nduced transparency provded a dspersve reference. A frequency error sgnal was obtaned by FM demodulaton [11, 6]. The error sgnal s returned to the external error nput on the probe laser MOGLabs DLC, whch locked the laser wth bandwdth up to about 40 khz. The error sgnal was also coupled through a sngle stage passve phase-lead (hgh-pass) flter, and then combned wth the 10 MHz modulaton usng a passve bas tee, and njected nto the SMA modulaton nput, to provde feedback bandwdth of about 600 khz. * RBW 300 Hz Ref -53 dbm -55 * Att 25 db AQT 200 ms Center GHz 75 khz/ Span 750 khz Fgure E.3: RF beatnote from two MOGLabs DLC-locked lasers. The 3 db peak wdth was 750 Hz wth a spectrum analyser RBW settng of 300 Hz. For a 20 s average, the wdth was about 4 khz.

76 64 Appendx E. External modulators and njecton current modulaton

77 F. Photodetector The MOGLabs photodetector, shown below, can be used as a sngle detector, or as a dfferental par (nternal DIP swtch 8). The photodetector s connected va the rear socket and cable provded. A number of M4 and 8-32 threaded holes allow mountng n dfferent confguratons to mnmse the footprnt on an optcal bench (see fgure F.2). Fgure F.1: MOGLabs DLC balanced dfferental photodetector Fgure F.2: M4 mountng holes are marked wth a dmple; others are Sngle channel photodode 1, dfferental sgnal

78 66 Appendx F. Photodetector F.1 Photododes The standard photodetector uses S-PIN photododes encapsulated n a coloured plastc whch transmts n the near-nfrared and blocks most room lght. The dodes nclude a lens to reduce the acceptance angle to ±10. Unfltered dodes, and wder acceptance angles, are also avalable. Photodode Specfcatons Parameter Standard Optons Spectral range(10% of max) nm nm Peak senstvty 900 nm 850 nm Half angle ±10 ±20 ; ±75 Senstve area 1 1 mm 2 Max ncdent power 500 µw Apparent senstvty (CHAN A) 30 mv/µw Relatve detecton effcency (%) Relatve detecton effcency (%) λ (nm) λ (nm) Fgure F.3: Photodode spectral response, standard fltered and unfltered.

79 G. Laser head board A laser head nterface board s provded to allow convenent connecton breakout to the laser dode, TEC, temperature sensor, pezo actuators, and laser head nterlock. It also ncludes a sold-state protecton relay and passve protecton flters, a laser-on LED ndcator, and an SMA connecton for drect dode current modulaton va a mcrowave bas-tee. The laser head board can be mounted to the suppled laser head panel. Two versons are avalable; please refer to the MOGLabs laser user manual for nformaton on the board provded wth MOGLabs lasers. Fgure G.1: MOGLabs DLC laser head board showng headers for connecton of laser dode, pezo actuators, temperature sensor, TEC and head enclosure nterlock. G.1 Headboard connectors P1 P3 HD1 HD2 HD3 HD4 HD5 HD6 HD7 HD8 Mcrowave RF modulaton nput (SMA) Dode (SMA, hgh bandwdth) Dode (MOLEX, low bandwdth) Actve temperature sensor (AD590 or AD592) Pelter TEC Interlock; laser dsabled unless short-crcuted Thermstor temperature sensor, 10 kω Prmary pezo STACK Pezo DISC Secondary pezo STACK 67

80 68 Appendx G. Laser head board Note only one temperature sensor should be connected. For hgh bandwdth RF modulaton (see below), the dode should be connected to the SMA connector (P3) rather than to the MOLEX HD1. Another very small crcut board, to connect drectly to the dode, s also avalable from MOGLabs, wth SMA and MOLEX connectors. The MOGLabs DLC does not provde a mechansm for optcal power control or measurement for dodes wth an nternal photodode. G.2 Dual pezo operaton The DLC provdes outputs to two pezo elements. They can be confgured as: Sngle Typcally, only a sngle stack actuator, such as the Tokn AE0203D04 (avalable from Thorlabs, wll be requred. The sngle stack actuator allows frequency scannng and frequency offset selecton, and actve slow feedback (up to 100 Hz). Normally STACK HD6 s used. Alternate sngle channel If there s a falure of the STACK electronc drver, t s possble to use the DISC drver. To change to the alternate hgh voltage drver: Connect the STACK pezo actuator to HD7 Insert a 0R0 resstor, sze 0603, for R602 Remove R601 (nomnally 10R0) Change R372 from 30k0 (sze 1206) to 270k (STACK at 120 V) or 390k (STACK at 150 V) (see LK2, p.15). Adjust RT7 fully clockwse. Two channel The DLC feedback servos nclude a second channel for hgh-speed pezo feedback, typcally to a dsc actuator. Ths would be connected to HD7. Parallel The DISC channel can nstead be used to drve a second STACK actuator, for example to allow smultaneous translaton

81 G.3 RF couplng 69 and tlt of a dffracton gratng, to ncrease the mode-hop free tunng range. Ths s the default confguraton for Rev For earler revsons, to actvate ths mode: Connect the second STACK to HD7 Insert a 0R0 resstor, sze 0603, for R602 Remove R601 (nomnally 10R0) Change R372 from 30k0 (sze 1206) to 270k (STACK at 120 V) or 390k (STACK at 150 V) (see LK2, p.15). Adjust RT7 to vary the relatonshp of the potental to the second pezo from 0.3 to 1.0 tmes the potental on the man STACK. G.3 RF couplng The SMA connector on the laser head board allows hgh-frequency current modulaton. The RF nput s AC coupled, wth low- and hghfrequency lmts of about 30 khz and 2.5 GHz (see fg. A.1). Capactor C4 s now (Rev ) 47 nf; earler revsons used 100 pf. C4 can be changed to adjust the low-frequency cutoff. For hgher bandwdths, use an external bas-tee such as the Mn-Crcuts ZFBT- 4R2GW-FT between the head board and the dode. From Rev. 9.01, the nput senstvty has been reduced by a factor of approxmately 20 compared to earler revsons. The nput mpedance s 1 k. The senstvty depends on the dode mpedance but s now typcally around 1 ma/v. WARNING: The RF nput s a drect connecton to the laser dode. Excessve power can destroy the dode. It s separated from the head board relay by an nductor, and thus the relay does not provde protecton from hgh frequency sgnals.

82 70 Appendx G. Laser head board r e s a L r + o t s m r e h T r - o t s m r e h T r + e t l e P r - e t l e P o + z e k P c a t S o - z e k P c a t S o + z e c P s D o - z e c P s D r - e s a L r + e s a L y - a l e R y + a l e R D E L 5 R R t u p n t I n e r r u r C e s a F L R A M e S l a m e F r 2 a P 1 r 2 a P 2 d l e h 4 S / 2 P 3 r 4 a P 4 r 4 a P 5 e 1 l g n S 6 e 2 l g n S 7 e 3 l g n S 8 r 1 a P 9 r 1 a P 0 1 d l e h 3 S / 1 P 1 1 r 3 a P 2 1 r 3 a P 3 1 e 5 l g n S 4 1 e 6 l g n S 5 1 e 4 l g n S 6 1 r 0 a P 7 1 r 0 a P 8 1 d l e h 5 S / 0 P 9 1 r 5 a P 0 2 r 5 a P 1 2 d l e h 6 S P 2 2 r 6 a P 3 2 r 6 a P 4 2 e l o t H n u o M 1 D D H R3 50R 4 R R 3 4 I N D 2 D r + o s n e e s v t c A r - o s n e e s v t c A g S d n G 1 P P A - 5 M S k c o l r e t n r I e s a L k c o l r e t n n o t s o d p L t c a t n o e c e r e F g a t l o V x o n b e h s w e s o l t c a h t n o t s o n p D H s d a e g l n y l F 2 R 9 9 k 4 4 C 47nF V g S d n G 3 P P A - 5 M S R F h g h b a n d w d t h c o n n e c t o n t o d o d e 1 L 3.3uH 1.9A C N A 1 U C N B 1 U 1 R R v 5 P v 5 P v 5 P h t r a s E s s a h C d l e h S d l e h S d l e h S d l e h S v 5 P d n G R6 1k0 Fgure G.2: MOGLabs DLC laser head board schematc. The RF modulaton low-pass cutoff frequency s determned by C4 and the dode mpedance ( 50Ω).

83 H. Feedback overvew ~ 250kHz Front panel Phase adjust Sne ref Phase Rear panel Imod Dther current range RT6 current dther gan Gan Dp 3 & front panel MOD Current dther enable Dode current dther Mod out Front panel MOD Dther on/off Demodulator Front panel Photodode offset Phase mdpont polarty control Test H/W Sne ref Frewre 6 pn Photodetector Rear panel External sgnal error/current Inamp Dp 8 Dfferental PD Input sgnal +/- +/- Dp 5 External error enable Dp 7 DC lock enable Front panel Master gan Summer Error sgnal Front Panel Error offset Gan +/- Error offset Fgure H.1: Overvew of error sgnal. 71

84 72 Appendx H. Feedback overvew Rear panel Sweep frequency Sweep generator Dp 9 External sweep enable Rear panel BNC External sweep Front panel Frequency (stack offset) External sweep sgnal Error sgnal Buffer Gan +/- Pezo gan Gan Dp 15 External pezo control R113 5k External sweep sgnal Summer Front Panel Sweep ampltude Stack offset Summer External sweep sgnal Stack pezo sgnal Dp 10 Stack polarty Front panel or DI-2 Scan/Lock Dp 13 Stack sweep enable Track/Hold DI-4 (Hold) Gan +/- Dp 1 & Dp 2 Stack compensaton enable Dsc offset +/- Dp 11 Stack drve polarty Sweep level Dp 14 Dsc sweep enable Rear panel BNC Trgger out (TTL) HV Drver Laser DVI-D DL HV Drver d 2 /dt 2 d 2 /dt 2 Dp 1 Pezo fast control enable Dp 2 & NOT Dp 1 Pezo slow control enable Dsc pezo control Integrator Slow current sgnal Summer Fgure H.2: Overvew of slow feedback and pezo sgnals. Note that resstor R113 s not nstalled by default.

85 73 Dp 12 Bypass AC RT12 Phase gan Front Panel Current gan Error sgnal Integrator Phase lead Gan +/- Buffer +/- Front panel Current polarty Phase mdpont polarty control Rear panel - BNC External Sgnal Error / Current Slow current sgnal 100uA/V Current control 2.5mA/V Dp 6 External current enable Dp 16 Pezo current enable Front panel or DI-3 Current control enable FAST Summer Front Panel or DI-1 Current regulator enable soft start Current Regulator Dsplay : Current Actual & Lmt (-) Dode Voltage Rear panel Current lmt Front panel Current setpont Laser DVI-D DL cable Front panel Bas gan Sweep level Gan Dp 4 Bas enable Dode current dther Fgure H.3: Overvew of fast feedback and dode current sgnals.

86 74 Appendx H. Feedback overvew

87 I. Connector pnouts I.1 Laser WARNING: The LASER connector s a standard DVI-D Dual Lnk socket as used for consumer dgtal dsplay devces. It should only be connected to the correspondng MOGLabs laser head board. It supples the hgh-voltage sgnals to drve the laser pezoelectrc actuators. The pezo drvers wll be dsabled f the cable s dsconnected, but nevertheless consderable care should be taken to ensure that non-moglabs devces are not connected va ths connector. The MOGLabs cable can be replaced wth a standard dgtal DVI-D Dual cable. There s a bewlderng assortment of apparently smlar cables avalable; only hgh qualty dual-lnk dgtal DVI-D cables should be used. Pn Sgnal Pn Sgnal Pn Sgnal 1 TEC 9 DIODE 17 DISC + 2 TEC + 10 DIODE + 18 DISC 3 Sheld 11 Sheld 19 Sheld 4 TEC 12 DIODE 20 STACK + 5 TEC + 13 DIODE + 21 STACK 6 AD590/ Relay GND 22 7 AD590/ Relay +5V 23 NTC 8 16 Interlock +5V 24 NTC Fgure I.1: LASER connector on rear panel. 75

88 76 Appendx I. Connector pnouts I.2 Photodetector The photodetector s connected va standard 6-pn IEEE-1394 (FreWre) connectors. Note that frewre cables swap pns 3,4 wth pns 5,6 so the pnout on the photodetector connector s dfferent to that on the controller. Pn Controller Detector 1 Ground 2 Dfferental f GND V Sgnal V Sgnal Sgnal +12 V 6 Sgnal + 12 V Fgure I.2: Photodetector connector on rear panel of DLC and correspondng connector on photodetector. Dfferental output s enabled f pn 2 s grounded (0 V). Sngle-ended s open-crcut or hgh (+12 V). Note that frewre cables swap pns 3,4 wth 5,6. I.3 Interlock The rear-panel nterlock socket s a standard 2.1 mm cylndrcal DC power jack. The outer conductor s suppled wth 5 V va a 5 k resstor. The nner pn s connected to ground va a 10 k resstor. The laser should be enabled by shortng the two contacts. LASER ENABLE ø2.1mm +5V/5k ø6.5mm Fgure I.3: INTERLOCK connector on rear panel.

89 I.4 Dgtal control 77 I.4 Dgtal control HD12 s a 10-pn header whch provdes access to several mportant control sgnals for lockng and for sample-and-hold of the lockpont, as descrbed n secton 2.6. The sgnals are standard TTLcompatble, > 2.4 V HIGH and < 0.8 V LOW. The nputs are ORed wth the front toggle-swtches, such that the sgnal s actvated f ether the dgtal nput s actve (.e. HIGH) or the toggle swtch s on (down). Pn Sgnal Pn 1 Laser ON/OFF 2 GND 3 Lock/Sweep 4 GND 5 Fast Lock 6 GND 7 Hold 8 GND 9 +5 V 10 GND

90 78 Appendx I. Connector pnouts

91 J. PCB layout L6 HD1 P5 C41 R102 R263 R100 D14 D16 R99 R111 R101 U27 R84 C10 L8 R15 D2 R5 R4 C5 U115 RV1 R44 TR2 C14 U118 R440 R218 U11 R25 R26 C20 D3 R47 R73 R559 R60 R78 HD12 U21 R578 U119 P1 C8 C160 RV7 R376 R375 HD6 C169 R386 R166 U117 R385 HD8 HD9 C152 D13 D15 C104 R272 C116 R312 U78 RV4 R279 C125 R295 RV5 R112 U116 R340 RV6 C141 R339 C134 H2 R313 C136 N3 C139 TR8 R256 U72 R262 TR9 TR10 D7 C111 C113 R276 R277 C126 R288 R296 U76 C121 K3 R284 R297 C72 C71 R162 C63 RV2 U110 R163 N20 R212 R64 R70 RV3 R193 R200 R205 R206 C80 HD4 C84 R209 R228 ZD2 C99 U55 C93 TR6 C94 HD2 HD3 R152 R153 R154 R603 R121 R606 U29 R160 TR3 R156 R155 R164 R167 U44 TR4 R158 C67 U45 R157 C69 C151 R197 R552 R219 R226 R225 R139 R149 U54 R176 R187 C107 U62 U108 R336 U109 R234 C102 RS1 R356 R113 L10 L12 R173 R174 U58 C127 C75 R169 R172 C42 R104 SW2 R103 C46 R106 R108 R94 R105 R107 U30 R132 R123 R131 U46 R124 U47 R135 R255 R89 C64 R602 C70 R210 R179 R201 R202 C86 R180 U50 C82 R203 U56 TR7 R229 C100 ZD1 C95 C96 C105 L14 R181 R183 R194 RT12 R186 R185 U51 R214 C88 R207 U52 R215 C89 R196 R195 C81 C74 C76 U53 C77 R208 R505 U111 R242 R222 R241 R217 R216 R230 U59 R221 U60 R239 R247 C106 R249 C101 R245 R246 R590 C90 R224 R220 R238 R248 U61 R223 R233 R243 R184 C43 R454 R114 C239 R115 R592 R593 R595 R594 U31 U32 U33 R598 R596 C54 C44 R599 R109 C45 R96 C39 R110 R98 U34 R128 C49 R136 R117 R116 R120 U35 R129 C52 R134 R143 C59 R452 R597 C240 R126 R159 U39 R168 R175 R144 R127 U113 U37 C50 R137 R138 R148 R130 C57 R150 R145 R146 R170 U40 R557 R147 R555 U41 R171 C131 R310 R341 D9 C147 R257 TR11 D8 C114 C108 U65 C110 L15 U77 C122 K2 R298 R280 U71 C123 K4 C142 H3 H4 C145 K6 U92 H5 R314 HD5 U79 R321 C135 D10 L18 C140 R320 U91 R322 U80 R328 U81 C133 R330 R329 R335 U87 N2 R342 R343 C146 R347 C148 R348 R351 R352 C150 U95 R350 R358 TR13 R349 R354 D1 TR14 U93 R353 R359 U96 R361 R360 U97 U66 R264 U67 R250 R258 R266 C115 R252 C117 R251 R267 R271 R591 R269 U68 C119 U73 R31 C118 R278 C120 C124 R285 C431 R281 R286 R299 R309 L17 R289 R290 R300 R282 C129 R287 R304 N1 R291 R301 R302 C128 R303 R305 RT14 R315 R308 C109 RS2 R577 U69 R572 R576 R571 R589 R259 U70 R579 R261 R270 R511 R260 R604 R607 RS3 R575 N23 N22 R283 R331 L16 P17 R273 U74 R275 U75 RS4 R292 R274 RT13 R306 U82 R332 C132 U83 R323 C137 R324 R344 R333 R311 U84 R318 R316 C138 R325 R326 R317 R319 C144 U88 C143 U86 R49 RT15 U94 R357 R362 R337 U89 R338 U90 R345 TR12 R346 K5 H6 R327 C149 P18 P15 C56 C65 R177 RT10 C38 R97 R93 R118 C47 C60 RT8 U28 C40 RT6 L9 U36 C48 R122 C55 R140 R151 R141 U38 R182 U42 C66 U43 C58 C61 R142 R161 C62 C73 L11 R165 C68 C78 R188 R178 R125 C427 C85 R190 R574 R211 R568 R7 R569 R199 R497 R192 U48 R198 TR20 C319 U57 U49 C91 R231 C321 R227 R236 R235 C98 R573 U63 TR5 R496 D31 L13 U64 R237 TR19 R495 R232 R254 C103 P13 R T11 C53 R119 P11 C51 C153 TR16 K7 H7 HD10 HD11 U98 R364 R365 R366 R363 R367 R543 TR15 C165 U99 C157 R544 C166 R583 R587 U102 C171 C155 R368 R372 C158 C156 N5 N7 R373 R56 D12 C154 R369 R371 R370 R588 R374 U100 C162 R584 R582 R377 C161 N21 R381 R564 R387 HD7 N8 R50 C168 R389 LK2 N6 R378 U101 R380 R383 R390 R384 R379 R382 R541 N10 D17 N9 R392 R581 R391 LK1 C159 C164 P20 C170 R388 U24 R16 R10 U114 R12 R13 R24 R408 R22 C36 R409 U1 U2 C12 C11 C9 R32 C17 U5 C15 R605 RT7 C21 C22 R27 U12 R30 C13 C25 R38 R39 R419 R45 C26 SW1 R48 R46 C29 TR1 R82 R86 R52 R51 R53 R55 U20 R83 C325 R580 R413 U6 U7 U13 R418 U16 R34 R41 R17 U14 R42 R601 U8 R28 U19 U18 R43 C27 U15 R61 R57 U17 R62 R40 R33 U22 R63 U23 R74 R54 C32 R66 C33 R75 R65 C37 R79 R87 R91 R1 L1 R3 R6 R2 L2 L3 L4 C3 C6 C7 R8 U3 R9 R410 U107 R14 R21 C4 C16 R561 R562 R600 C1 H1 C2 K1 U4 L5 R23 L7 R19 R20 C18 R29 U9 R37 R68 R59 R36 RT3 C35 U10 C19 C24 R35 C30 C28 RT4 C214 R67 C34 R58 R77 R76 R92 R69 R88 U25 R71 R72 RT5 R81 R80 U26 R85 D4 R90 RT2 RT1 P3 B1010 rev 9+ Man Board Dp Swtch Postons v I/O 0v FAN_IO 0v +12v 2*14 VAC + - T 2014 TO220_KIT c TO220_KIT 0v -12v - +12v + 0v -12v +5v 0v 1 JTag v TO220_KIT Ph. ON OFF +5v 0v +12v TO220_KIT Naux Paux - 0v + 0 ADJ 0v TO220_KIT Amp-D Y 0v X Amp-I Gan 0v TO220_KIT Earth 120 VAC Imax 160v 0v v B1010P139 0v 0v TO220_KIT Freq. Dst Amp 79

92 80 Appendx J. PCB layout

93 K. 115/230 V converson K.1 Fuse The fuse s a ceramc antsurge, 2.5A, 5x20mm, for example Lttlefuse MXP. The fuse holder s a red cartrdge just above the IEC power nlet and man swtch on the rear of the unt (Fg. K.1). Fgure K.1: 230 Vac. Fuse catrdge, showng fuse placement for operaton at K.2 120/240 V converson The controller can be powered from AC 50 to 60 Hz, 110 to 120 V (100 V n Japan), or 220 to 240 V. To convert between 115 V and 230 V, the fuse cartrdge should be removed, and re-nserted such that the correct voltage shows through the cover wndow. 81

94 82 Appendx K. 115/230 V converson Fgure K.2: To change fuse or voltage, open the fuse cartrdge cover wth a screwdrver nserted nto a small slot at the top of the cover, just above the red voltage ndcator. When removng the fuse catrdge, nsert a screwdrver nto the recess at the top of the cartrdge; do not try to extract usng a screwdrver at the sdes of the fuseholder (see fgures). Fgure K.3: To extract the fuse cartrdge, nsert a screwdrver nto a recess at the top of the cartrdge. When changng the voltage, the fuse and a brdgng clp must be swapped from one sde to the other, so that the brdgng clp s always on the left and the fuse always on the rght; see fgures below.

95 K.2 120/240 V converson 83 Fgure K.4: Brdge (left) and fuse (rght) for 230 V. Swap the brdge and fuse when changng voltage, so that the fuse remans on the rght-hand sde (see below). Fgure K.5: Brdge (left) and fuse (rght) for 115 V.