PP Automatic. Manual. APE - Angewandte Physik& Elektronik GmbH

Transcription

1 Synchronously Pumped OPO PP Automatic Manual APE - Angewandte Physik& Elektronik GmbH ape@ape-berlin.de Plauener Str Haus N Berlin Germany Phone +49 (0) Fax +49 (0)

2 Content 1. Description and Specifications Introduction Tuning Mechanism and Cavity Length Stabilization General Description of Optical Unit Intra Cavity SHG General Description of Control Electronics Crystal Tuning Curves and OPO-Specifications General Safety Optical Safety Electrical Safety Summary of Handling and Menus of the Control Electronics Unit Different Cavity Configurations Linear OPO Ring SHG OPO Idler Option Installation Length Prealignment Basic Installation Cavity Alignment Activation of Stabilization Unit Fast Alignment Routine for an Installed System (daily routine) Linear OPO Ring OPO...43 OPO PP Auto Manual # September 2008

3 7. Laserspectrometer WaveScan Specifications Technical Description Set-up Handling How can I Troubleshooting Theory of Optical Parametric Conversion and the OPO PP Automatic...52 Appendix A: Lists of OPO mirrors, Dispersion Blocks and Crystalls...55 Appendix B: OPO PP Automatic - RS232 Command Set...60 Appendix C: Exchange of Mirrors in Mount M1 and M Appendix D: Accessoiries / Alignment Apertures...67 Appendix E: Mini Autocorrelator (optional)...71 OPO PP Auto Manual # September 2008

4 1. Description and Specifications 1.1. Introduction The APE OPO is an Optical Parametric Oscillator synchronously pumped by a modelocked Ti:Sapphire laser. It is based on collinear, quasi phase matched interaction in a periodically poled crystal (PP crystal). The OPO is designed for a highly efficient frequency transformation from the Ti:Sapphire range to nm (signal) and further to 3.4 µm for the idler wavelength. The Ring version of the OPO additionally offers highly efficient intracavity SHG generation of the IR OPO signal to the visible wavelength ranged (VIS nm). The OPO is tuned by cavity length de-tuning and generates trains of femtosecond or picosecond pulses. Since this process is jitter free it is very convenient for two color experiments as e.g. pump and probe measurements. For a list of crystals and optics sets including their tuning curves see chapter 1.6. This manual describes the OPO PP Automatic with its different configurations. All cavity options and wavelength ranges described in this manual are interchangeable and upgradable Tuning Mechanism and Cavity Length Stabilization PP crystals have an extremely broad phase matching bandwidth, thus PP OPOs can generate a broad wavelength range with a fixed pump frequency. They are either tuned by intracavity gratings, birefringent filters or by cavity length de-tuning using the intrinsic GVD of the crystal. This effect occurs because the cavity round-trip time for the signal pulse depends on wavelength through the contribution of the group velocity inside the crystal. The last method is by far the most elegant one, because it is simple and allows for fast tuning. To enhance the effect an intracavity block of a heavy flint glass is added as an additional dispersion element. Thus the broad phase matching bandwidth is still maintained with suitable short PP crystals while the additional group velocity dispersion is leading to well separated spectra with nearly transform limited pulses which are easily tunable by cavity length de-tuning. By varying the length of the crystal and of the dispersion elements, the system is adaptable to fs- (~ fs) or ps-operation (~1.50 ps) or even ps long pulse operation(~5 ps pump). In fs-operation the phase matching bandwidth is big enough to cover the whole tuning range with one specified pump wavelength. Longer crystals are needed in ps-operation for the gain due to lower peak power, but this decreases the phase matching bandwidth and therefore the tuning of the OPO. For a 6 mm crystal and 1,5 ps pump pulses typically nm can be addressed with one pump wavelength and one PP-period. But with shifting the pump wavelength a few nm the whole nm range can be covered (for a PP830 crystal). For the generation of the visible output in the Ring version the IR radiation is intracavity frequency doubled with a LBO crystal. To reach the necessary high energy density this crystal is OPO PP Auto Manual # September 2008

5 located in a second beam waist within the cavity. To operate the SHG crystal at optimum phase matching condition its temperature is tuned. Since a cavity length mismatch is influencing the signal wavelength, a fraction of the signal wavelength is used to stabilize the cavity length. When passing the beam splitter BS, 1% of the beam intensity is diffracted towards the beam steering mirror SM and from there into the spectrometer. This spinning grating spectrometer is measuring the spectrum of the OPO signal. The central wavelength is then compared with the set wavelength by the controller and the cavity length is changed by a piezo element if necessary. To change the wavelength in locked position just enter a new set value into the control electronics or with a remote computer via RS232. You can also change the wavelength manually by changing the piezo voltage with the big rotary knob. In this case the wavelength is not stabilized General Description of Optical Unit The APE OPO PP Automatic consists of the optical unit and the control electronics console. The optical unit is schematically shown in Fig. 1 for the Linear version and Fig. 2 for the Ring version with intracavity SHG. It contains Brewster windows for pump radiation input and OPO radiation output, pump beam focussing optics, sensor modules, a 5 mirror cavity with one beam waist for the Linear Version and a variable 8 mirror cavity with two beam waists for the Ring version respectively. In order to synchronize the cavity round trip time to the pump laser repetition rate, one of the mirrors is mounted on a translation stage combined with a piezo fine alignment element (PZT) for active cavity length stabilization. Fig. 1 Linear OPO, Optical Unit with internal spectrometer OPO PP Auto Manual # September 2008

6 Fig. 2 Ring OPO, Optical Unit with (external spectrometer) 1.4. Intra Cavity SHG For the Second Harmonic Generation a non-critical phase matched (NCPM) LBO crystal (type I) is used due to its high conversion efficiency. The phase matching is temperature tuned. Its characteristic is shown in Fig LB O -phase m atching tem perature 180 phasematching temperature / C h e a te r T E C O P O / n m Fig. 3 Optimum phase matching temperature for the LBO-SHG crystal The temperature is varied and stabilized by an oven or a thermoelectric cooler (TEC) according to the chosen wavelength range. They are driven and stabilized by a temperature control electronics unit which is part of the control electronics console shown in Fig. 4. OPO PP Auto Manual # September 2008

7 The LBO SHG-crystal together with a temperature sensor is mounted on a 4-axis alignment element and is placed in the second beam waist between CM3 and CM4. The oven is mounted directly in the crystal mount and the TEC is mounted on a motorized and water cooled stage, which has to be connected to the thermostat water loop of the pump laser. For high temperatures the TEC has no contact with the crystal mount and the temperature is controlled by the oven. For lower temperatures (below approx C) the oven will be switched off and the TEC will be motor driven to the crystal mount General Description of Control Electronics Description and Cabling of the Control Electronics The control electronics console is shown in Fig. 4 and Fig. 5. It contains the piezo driver, the diagnostics control boards (spectrometer and an optional autocorrelator), the sensor amplifier, the necessary control elements and a temperature control unit for the SHG crystal in case of a SHG- Ring version. Fig. 4 Control Electronics Console OPO PP Auto Manual # September 2008

8 Fig. 5 Rear Panel The OPO PP Automatic is controlled with two rotary knobs, 6 soft keys with their actual function displayed at the right edge of the screen, 5 keys with fixed function and a power switch in the lower left corner. At the rear panel you have the following connectors: Label Cable type Connect to Power Mains Thermo 7-pin round 9-pin Sub-D OPO optical unit (thermo modules, Ring only) System 25-pin Sub-D OPO optical unit (sensors + spectrometer) Monitor 1 BNC Oscilloscope VIS power (0-10 V DCoutput) Monitor 2 BNC Oscilloscope IR power (0-10 V DC-output) U PZT SMA HV-BNC OPO optical unit (Piezo voltage) Spectrometer 15-pin Sub-D external spectrometer optics (optional) RS232 9-pin Sub D RS232-port of computer for remote control AC Optics 25-pin Sub-D Autocorrelator optics (optional) AC Delay BNC Oscilloscope AC Intensity BNC Oscilloscope AUX for service purposes only OPO PP Auto Manual # September 2008

9 Description and Cabling of the Optical Unit Pump Input Water Flow Indicator Thermo System Purge Out In Water Piezo Fig. 6 PP-Auto Optical Unit, pump side with electrical connectors, purge input and water in- and output Fig. 6 shows the pump side of the optical unit. All the cables from the control electronics to the optical unit have to be connected on this side, such as the Piezo-cable, the 25 pin Sub-D cable for the system and in the SHG-Ring configuration the 9 pin Sub-D side of the Thermo cable. The purge input (dry air or nitrogen) is marked with a green ring. Purging is necessary due to water absorption of the IR radiation and due to the hygroscopic SHG crystal (Ring version). In case of a Ring version the water needs to be connected in line with the pump laser system for heating / cooling the SHG crystal. The water inlet is marked blue, the water outlet is marked red. OPO PP Auto Manual # September 2008

10 Inside the OPO there is a distribution board, where the internal spectrometer and the power sensors are connected to. This board is shown without cover in Fig. 7. Further on this board there are two gain control potentiometers for the IR- and VIS power sensors. Also the humidity sensor is placed on this board and a red LED is illuminated if no water flow is detected (the heater / cooler unit will be deactivated in this case). IR Sensor Gain VIS Sensor Gain Water Flow Detector Spectrometer VIS Power Sensor IR Power Sensor Fig. 7 Sensors and spectrometer connectors on distribution board in the OPO optical unit (shown without cover) OPO PP Auto Manual # September 2008

11 1.6. Crystal Tuning Curves and OPO-Specifications Tuning range (nm): Pump Signal (resonant) Signal SHG 1) Idler (non-resonant) Standard crystal PP ± Standard PP ± 10 Extension crystal PP ± Mira + Verdi V5 Mira + Verdi V10 Chameleon Ultra Mira HP Signal output 1300 nm mw mw mw mw Ring SHG output 600 nm mw mw mw mw Threshold mw 2) Pulse duration..... typ fs pump pulse typ ps pump pulse Time-bandwidth product typ. 0.6 Polarization..... horizontal for Signal and Idler, vertical for VIS-SHG Noise <1 % RMS Repetition rate..... appr. 76 / 80 MHz, subject to pump laser repetition rate (others on request) Beam height mm Spectrometer..... IR version IR/VIS version resolution integrated into optics unit.... external ,2 nm nm nm Beam Parameters (typical 1300nm) Spatial mode TEM 00 M² Beam diameter mm Divergency mrad Size (W*L*H in mm).. Optical unit 402 x 1139 x Control electronics 290 x 185 x 280 1) Ring with intracavity - SHG 2) low power systems; optimized for Mira + 5 W Verdi pump OPO PP Auto Manual # September 2008

12 2. General Safety 2.1. Optical Safety Laser light, because of its special properties, poses safety hazards not associated with light from conventional sources. The safe use of lasers requires that all laser users, and everyone near the laser system, are aware of the dangers involved. The safe use of the laser depends upon the user being familiar with the instrument and the properties of coherent, intense beams of light. Direct eye contact with the output beam from the laser will cause serious damage and possible blindness. The greatest concern when using a laser is eye safety. In addition to the main beam, there are often many smaller beams present at various angles near the laser system. These beams are formed by specular reflections of the main beam at polished surfaces such as lenses or beam splitters. Although weaker than the main beam, such beams may still be sufficiently intense to cause eye damage. Laser beams are powerful enough to burn skin, clothing or paint. They can ignite volatile substances such as alcohol, gasoline, ether and other solvents, and can damage light-sensitive elements in video cameras, photomultipliers and photodiodes. The laser beam can ignite substances in its path, even at some distance. The beam may also cause damage if contacted indirectly from reflective surfaces. For these reasons and others, the user is advised to follow the precautions below. 1. Observe all safety precautions in the pre-installation and operators manual. 2. Extreme caution should be exercised when using solvents in the area of the laser. 3. Limit access to the laser to qualified users who are familiar with laser safety practices and who are aware of the dangers involved. 4. Never look directly into the laser light source or at scattered laser light from any reflective surface. Never sight down the beam into the source. 5. Maintain experimental setups at low heights to prevent inadvertent beam-eye encounter at eye level. Laser safety glasses can present a hazard as well as a benefit; while they protect the eye from potentially damaging exposure, they block light at the laser wavelengths, which prevents the operator from seeing the beam. Therefore, use extreme caution even when using safety glasses. OPO PP Auto Manual # September 2008

13 6. As a precaution against accidental exposure to the output beam or its reflection, those using the system should wear laser safety glasses as required by the wavelength being generated. 7. Avoid direct exposure to the laser light. The intensity of the beam can easily cause flesh burns or ignite clothing. 8. Use the laser in an enclosed room. Laser light will remain collimated over long distances and therefore presents a potential hazard if not confined. 9. Post warning signs in the area of the laser beam to alert those present. 10. Advise all those using the laser of these precautions. It is good practice to operate the laser in a room with controlled and restricted access Electrical Safety The Mira-OPO uses DC voltages in the laser head. All units are designed to be operated with protective covers in place. Certain procedures in this manual require removal of the protective covers. These procedures are normally used by a qualified trained service personnel. Safety information contained in the procedures must be strictly observed by anyone using the procedures. Pump Source Observe all safety precautions associated with the pump laser. Refer to the pump laser operators manual for additional safety precautions. Safety Features and Compliance to Government Requirements The following features are incorporated into the instrument to conform to several government requirements. The applicable United States Government requirements are contained in 21 CFR, subchapter J, part II administered by the Center for Devices and Radiological Health (CDRH). The European Community requirements for product safety are specified in the Low Voltage Directive (published in 73 / 23 / EEC and amended in 93 / 68 / EEC). The Low Voltage Directive requires that lasers comply with the standard EN Safety Requirements For Electrical Equipment For Measurement, Control and Laboratory Use and EN Radiation Safety of Laser Products. Compliance of this laser with the requirement is certified by the CE mark. Laser Classification The governmental standards and requirements specify that the laser must be classified according to the output power or energy and the laser wavelength. The Mira-OPO is classified as Class IV based on 21 CFR, subchapter J, part II, section (d). According to the European Community standards, the Mira-OPO is classified as Class 4 based on EN , clause 9. In the manual and other documentation of the Mira-OPO, the classification will be referred to as Class 4. OPO PP Auto Manual # September 2008

14 Protective Housing The laser head is enclosed in a protective housing that prevents human access to radiation in excess of the limits of Class I radiation as specified in the Federal Register, July 31, 1975, Part II, Section (f) (1) and Table 1-A/EN , clause 4.2 except for the output beam, which is Class IV. Use of controls or adjustments or performance of procedures other than those specified in the manual may result in hazardous radiation exposure. Use of the system in a manner other than that described herein may impair the protection provided by the system. Location of Safety Labels Refer to figure 32 for a description and location of all safety labels. These include warning labels indicating removable or displacable protective housings, apertures through which laser radiation is emitted and labels of certification and identification [CFR (g), CFR , and CFR /EN , Clause 5]. When the pumping beam is allowed to impinge on the titanium: sapphire crystal, both laser and collateral radiation are produced. The laser beam is emitted from the laser aperture which is clearly labeled. OPO PP Auto Manual # September 2008

15 AVOID EXPOSURE VISIBLE AND INVISIBLE LASER RADIATION IS EMITTED FROM THIS APERTURE Fig. 8 Safety Features and Labels The laser is designed to be used with the covers in position and this cover shields the operator from all collateral radiation. During initial alignment and maintenance operations, such as mirror alignment, it will be necessary to remove the covers. The covers are not interlocked with the circuitry of the pumping laser but a label provides a warning about exposure to the radiation. Operation of laser with covers removed will allow access to hazardous visible and invisible radiation. The laser housings should only be opened for the purposes of maintenance and service by trained personnel cognizant of the hazards involved. Extreme caution must be observed in operating the laser with covers removed. There are highpower reflections which may exit at unpredictable angles from the laser head. These beams have sufficient energy to cause permanent eye damage or blindness. OPO PP Auto Manual # September 2008

16 3. Summary of Handling and Menus of the Control Electronics Unit This paragraph gives you a summary of the software control and setup functions of the control electronics including the menu structure and the display values. In the main menu there is a continuous display of the most important parameters on the screen: Display Meaning Range λset nm top line: If the system is in automatic operation, the set wavelength will be shown in red in the centre of the display. wavelength locked Left margin, middle wavelength and right margin of spectrometer window (position and zoom of spectrometer) bottom line: for Ring systems only: T(SHG)s SHG-crystal set temperature C T(SHG)a actual SHG-crystal temperature temperature locked lower right corner: RH= lower left corner relative humidity SGAIN= Current spectrometer gain (1, 3, 10, 30, 100, 300) for autocorrelator option only: SCAN150fs displays the selected autocorrelator scan range 150fs, 500fs, 1.5ps, 5ps, 15ps (P) GAIN 152 shows the autocorrelator gain setting P-Preamp on, GAIN Further all important OPO parameters can be selectively displayed, such as the central wavelength λcentr, the FWHM of the spectrum ( λ), the set wavelength (λset), the output power and the piezo voltage, see UTILITY MENU. OPO PP Auto Manual # September 2008

17 Key- and Menu functions: 1. Power on/off..... Push button down left on front panel 2. MAIN / RETURN.... push buttons on the right hand side below the screen The MAIN button leads to the main menu, the RETURN button to the previously used menu. 3. There are 2 combined rotary / push button knobs for setting parameters. Pushing the knobs usually changes the resolution of the rotary knobs from 1 to 10 to 100 if applicable. The large blue rotary knob in the lower right corner (TUNING) is used for the setting of the piezo voltage and the set wavelength. In case the blue knob has to be used the menus are in blue. All other values (menu in black) are set by the black rotary knob (SET). 4. Main menu - OPO control.... Main menu OPO MENU - Spectrometer control.... Main menu SPECTRUM MENU - Utilities, display.... Main menu UTILITY MENU - Run / stop spectrometer.. Main menu --> RUN>>>STOP 5. OPO control 5.1 Manual cavity length control - Piezo voltage (direct).... Large blue rotary knob 5.2 OPO MENU - PIEZO MANUAL.... in this mode the OPO is not wavelength stabilized, the cavity length can be set manually with the blue rotary knob by changing the piezo voltage with a resolution of By pressing the rotary knob the resolution of the knob changes. - SET LAMBDA.... when pressing this button, the desired wavelength can be entered with the blue rotary knob. The resolution of the knob is changed by pressing the knob from nm to 1 to 10 to 100 nm. The set wavelength will be activated and stabilized by pressing ACTIVATE - ACTIVATE..... if possible, the displayed set wavelength will be activated and stabilized (λcentr λset). - HYSTERESIS.... gives the deviation from the set wavelength, which the controller accepts without actively readjusting the OPO- wavelength (to be set with the black rotary knob). OPO PP Auto Manual # September 2008

18 - Temp shg (Ring SHG OPOs only) setting the temperature of the SHG crystal (black rotary knob); the set value T(SHG)s and the actual temperature T(SHG)a are shown on the display. The temperature stabilization unit is always active in the Ring SHG mode and stabilizes T(SHG)a to T(SHG)s. 6. Spectrometer control 6.1. Direct spectrometer controls: - Spectrometer Gain.. +/- buttons left below the display (direct), in steps 1, , 10, 30, 100, CURSOR..... button in the middle below the display opens the Cursor Menu. If the window position cursor or no cursor at all is activated, the black rotary knob shifts the middle wavelength of the displayed spectrum(if the spectrum range is not set to maximum). This wavelength is displayed in red in the middle of the top line on the display. - SPEC CURSOR.... CURSOR SPEC CURSOR: gives the opportunity to measure the spectral bandwidth FWHM and the peak wavelength manually with cursors. They are selected by the buttons HOR1 to VERT2 (the selected cursor is highlighted) and moved by the black rotary knob SPECTRUM MENU - ZOOM ZOOM the display width is shown beside the button (from 10 nm to maximum spectrum range (all), use black rotary knob); the left and right margins are shown in the top line of the display (in red) - WINDOW POSITION... changes the middle wavelength of the displayed spectrum (if the spectrum range is not set to maximum) Use black rotary knob. - Spectrum smoothing... SMOOTH ON / OFF, averaging over 4 adjacent wavelength points to smooth spectrum, resolution will be reduced for narrow spectra below 1 nm by 0.1 nm (i.e. from 0.2 nm to 0.3 nm) OPO PP Auto Manual # September 2008

19 - SPECMODE SIGNAL>>PUMP changes the sensitive range of the spectrometer from approx nm for the signal range to nm for the pump wavelength. In case of SHG-Ring option the spectrometer range further will be changed to the VIS range from 480 to 750 nm The PUMP option can be used to monitor the pump wavelength. This would interfere with the OPO wavelength stabilization mode if sensitive in the Signal range. When the SPECMODE PUMP is switched on, on the top line λpump is written in red. Also the stabilization of the OPO will be deactivated. - SPECTROMETER OFFSET.. changes the offset of the spectrometer signal (black rotary knob) for each electronic gain setting Attention: Only gain settings 1, 10 and 100 are electronic gain settings. (3, 30 and 300 are just numerical). Make sure the baseline is not negative and within 1/10 of the lower screen. 7. UTILITY MENU - Display OPO.... gives the choice of OPO parameters shown on the display, such as Piezo voltage, humidity and power values - display spec.... changes the display of the spectral parameters: spectrum display, central wavelength, peak wavelength and FWHM of the spectrum - DISPLAY ACF.... display parameters of the autocorrelator (optional), such as autocorrelation trace (ACF), FWHM pulse length display (only applicable for systems with autocorrelator option) - SERIAL PORt... setting the RS232 baud rate for computer control (other RS232 parameters are: 8 data bits, no parity, 1 stop bit) - CONFIG The current OPO configuration used must be set here: fs-ir, ps-ir, fs-vis or ps-vis. This... will influence the tuning and stabilization algorithms.. and time constants as well as temperature..... stabilization access. - Bright changes the display intensity and contrast OPO PP Auto Manual # September 2008

20 8. CORR MENU Autocorrelator control (optional) All autocorrelator functions can be found in the CORR MENU on successive menu pages. By pressing the corresponding soft key a function is activated (highlighted) or set to the alternative status respectively. Once the function is activated, the according parameter can be changed by tuning the set-knob. Page 1 - ACF Gain m.. controls the gain of the AC intensity - ScanRange n.. control and display of actual scan range - Smooth off>>on activates or disables average over 3 adjacent data points -Average k.. activation of the average of k ACF traces -Filter on>>off.. turns off or on a low pass filter to suppress noise and fringes -Next.... switches to next menu page Page 2 - ACF offset nn controls the AC-intensity offset - Scan offset mm controls the delay offset for centering the ACF Information about the Autocorrelator Mini handling and alignment you will find in the appendix. OPO PP Auto Manual # September 2008

21 4. Different Cavity Configurations The Linear OPO system has one cavity configuration only, whereas the Ring OPO system is designed for being used in two different cavity configurations: - Linear OPO for IR-generation, - Ring OPO for VIS-generation with a second beam waist for intracavity SHG. The Ring OPO can also be used for IR generation by replacing M2 with the appropriate output coupler and the SHG crystal with a dummy glass block. 4.1 Linear OPO The linear OPO has a folded 5-mirror cavity shown in Fig. 9. BW1 A1 L1 CM1 CM2 A2 M4 BS OPO Xtal BW2 M1 DP M2/OC K SP SM PD1 Fig. 9 Optical Unit - layout and optical elements A1, A2... apertures.... L1... pump focussing lens CM1, CM2... concave mirrors... OPO Xtal.. OPO crystal M1, M2, M4.. plane mirrors... OC... output coupler BW1, BW2.. brewster windows.. PD1... IR power photo detector SP.... spectrometer... DP... dispersion plate K..... cavity length adjustimg knob PZT.... piezo transducer BS.... beam splitter for spectrometer detection SM.... spectrometer beam steering mirror OPO PP Auto Manual # September 2008

22 Remark: BS, SM and the internal spectrometer are not always present. Especially in case of later upgraded systems, the spectrometer is outside the optic unit and uses a fraction of the beam with an external beam splitter Ring SHG OPO This Ring OPO has a folded 8-mirror cavity shown in Fig. 10. It has two beam waists, one for pumping the OPO crystal and another for efficient Second Harmonic Generation. BW1 A2 DP OPO Xtal M4 BW2 SHG Xtal M2/OC K Fig. 10 Ring Cavity OPO Construction A1, A2.. apertures..... L1... pump focusing lens OC... output coupler L2... SHG collimating lens CM1 - CM4.. concave mirrors.... PZT... piezo transducer M1 - M4.. plane mirrors.... BW 1 -BW3.. brewster windows DP... dispersion plate.... OPO Xtal.. OPO crystal SHG Xtal.. SHG-crystal or dummy crystal...pd3... VIS power photo detector K.... cavity length adjusting knob OPO PP Auto Manual # September 2008

23 4.3. Idler Option BW1 A1 L1 CM1 CM2 L3 A2 IF BS OPO Xtal M4 BW2 M1 DP M2/OC SP SM Fig. 11 In case the OPO is fitted with an Idler option, the Idler beam passes through CM2 (a specially designed Idler transmitting mirror). The collimating lens L3 is mounted on a translation stage to adjust the divergence of the Idler beam. The Idler output window (IF) is a long pass filter which only transmits the Idler. The residual pump beam will be blocked. OPO PP Auto Manual # September 2008

24 5. Installation 5.1. Length Prealignment - Put the OPO on your optical table behind your laser, place two beam steering mirrors (pump optic set + pump mirrors) between both instruments, so that the pump beam enters the window BW1 perpendicular and centred, - Level the OPO horizontally exactly to the height of the pump laser, - Start your pump laser at the desired time regime (ps or fs), - Measure the repetition rate of the pump laser with a frequency counter using a photodiode output signal, - Compare it to the frequency listed in the OPO test protocol for the desired configuration (linear/ ring, ps/fs), - Calculate the necessary cavity length change of the OPO by L = c / 2f REP - c/2 f TEST for linear configuration, L = c / f REP - c/ f TEST. for Ring configuration (positive values - cavity has to be longer, negative - shorter). To find the proper cavity length with different dispersion blocks take into account, that the material has a refractive index of about 2, - Change the position of the translation stage by the calculated value relative to the position listed in the OPO test protocol. Please note: smaller numbers on the micrometer reading refer to a longer cavity and lower repetition rates; larger numbers refer to a shorter cavity and higher repetition rates respectively. If the synchrony position is outside or near the end of the translation range of the mirror mount (25 mm), change position of the OC mirror mount base relative to the position listed in the test protocol. There are 3 positions on the translation stage A, B and C with 25 mm spacing and two positions on the piezo mounting plate 1 and 2 with 12.5 mm spacing, see Fig. 12. The two mounting positions of the mirror mount on the piezo are called I and II. They are separated by 32 mm, - The mirror mount can be turned on its own axis by 180 from back to front position. Please have in mind, that the mirror should be turned in the mount, when doing the change! The two positions front and back differ from...mm, - You also can change the repetition range of your pump laser by changing its cavity length. OPO PP Auto Manual # September 2008

25 Fig. 12 Different mounting positions A, B and C for M2/OC on the translation stage Fig. 13 Example for mounting position of M2/OC: position A1 II back OPO PP Auto Manual # September 2008

26 5.2. Basic Installation - Block the laser beam, - Remove lenses L1 (Fig. 14), mirrors CM1, CM2 (Fig. 15) and OPO crystall (Fig. 16), lens alignment screws Fig. 14 Fig. 15 Fig. 16 OPO PP Auto Manual # September 2008

27 BW1 SHG Xtal DP OPO Xtal M2/OC BW2 PD3 BW3 Fig Centre input beam with the beam steering mirrors on A1 and A2 (Fig. 17), - Put the lens L1 in its holder (Fig. 14) and recentre the spot on aperture A2 with the lens alignment screws, - Put mirror CM1 in its holder (plane side to the pump beam) (Fig 15), - Put mirror CM2 in its holder (concave side to the beam) (Fig 15), - Check the distance of the front edges of CM1 and CM2 (concave side):.. for fs-operation it should be 116 mm for pump power lower than 2 W,.. for ps-operation it should be 118 mm for pump power lower than 2 W,.. for fs-operation it should be 130 mm for pump power higher than 2 W,.. for ps-operation it should be 132 mm for pump power higher than 2 W, - Choose the desired OPO configuration (see chapter 4 and Appendix A) and set the necessary M2/OC mirror into the mount, choose the correct dispersion block, - Check the cavity length (see chapter 5.1.), - Ring configuration only: Check the distance of the front edges of CM3 and CM4 (concave side): for fs-operation it should be 104 mm,.. for ps-operation it should be 109 mm. If the distance is slightly not correct, turn concurrently all screws of the mount CM2 (4 rotations ~ 1 mm). For change of distance from 1o4 mm to 109 mm and vice versa unscrew the foot of the CM3 mirror from the base plate and use the two other mounting holes on the mount / base plate (shifted by 90 and 5 mm): for ps-operation the 2 screws of the CM3 foot are aligned parallel to the OPO front face, for fs-operation perpendicular. OPO PP Auto Manual # September 2008

28 Crystal mount: The nonlinear crystals used have a small aperture and their position need to be aligned exactly within the cavity. That is why the PP-crystal is mounted in an 3-axis translation- and 2 axis rotation holder (Fig. 18), the SHG- crystal (Ring systems only) is mounted in a 1-axis translationand 3 axis rotation holder (Fig. 26). All axis can be set manually Fig axis PP-crystal mount (left) and crystal holder (right), (1) horizontal x-translation micrometer screw, (2) horizontal y-translation adjustment screw, (3) crystal height, (4,5) crystal angle tilt adjustment screws, (6) crystal holder including the PP-crystal (rectangular) (the crystal at lower position will be in the beam), (7) PP crystals Block the pump beam. Then the PP-crystal holder (6) needs to be placed into the mount (PPcrystal down as shown in Fig. 16 and 18), the micrometer screw (1) has to be set to the value given in the test report and the PP-crystal needs to be centred in the pump beam with (2) and (3). Correct the tilt angle of the crystal with (4) and (5) by monitoring the pump beam back reflection. Align the crystal perpendicular to the beam (check with back reflection on aperture A1 or its interaction with the laser) and then tilt it vertically with tilt screw 4 in Fig. 18 down until the back reflection hits the lens holder L1. Besides the proper alignment of the optical axis of the cavity there are other conditions for the operation of the OPO: - the exact synchronism between the temporal distance of the pump pulses (pump laser repetition rate) and the cavity round trip time of the OPO. For best time-bandwidth product the use of the proper dispersion plate is essential, - the isolator needs to be installed for ps operation between A1 and L1, it has to be removed in fs-operation, - the following dispersion plates should be used (typical, please check installation protocol): in fs- mode: typically 6-12 mm (see test protocol) ps-operation: typically 24 to 36 mm for all wavelength ranges (see test protocol) long pulse ps-operation: typically 36 to 48 mm (see test protocol) OPO PP Auto Manual # September 2008

29 - Put the PP-crystal with holder in its mount see Fig. 18 (choose the right crystals for ps or fs operation), the crystal at lower position will be in the beam, - Check, if the beam hits the 1 mm thick PP-crystal centrally. If not, correct with the horizontal Y-translator of the crystal holder see Fig. 18), - Tune the pump laser wavelength to match with the PP-crystal (typically around 775 nm or nm, see test protocol) with approx. 1 W mode locked power or higher, - Open aperture A1. For crystals with required pump wavelength of 800 nm and below: The dispersion blocks inside the cavity do not transmit wavelength below 400 nm. Because of the use of the pump pulse SHG for alignment purposes, either take out the dispersion plates or tune the pump laser (for alignment purposes only) to above 820 nm. - Place the aperture between M1 and the dispersion block, monitor the SHG spot, and shift lens L1 until a clear spot is to be seen (look for smallest spot size). Alternatively you can set the crystal and lens position to the values given in the test protocol. - Place the correct output coupler (Appendix D) in the M2/OC mount Cavity Alignment Linear OPO Fig. 19 Linear OPO OPO PP Auto Manual # September 2008

30 - Align the crystal perpendicular to the beam with screws 4 and 5 in Fig 18 (check with back reflection on aperture A1 or its interaction with the laser) and then tilt it vertically with tilt screw 4 in Fig. 18 down until the back reflection hits the lens holder L1, BW1 BS OPO Xtal DP SP SM PD2 Fig Adjust CM2 to center spot on M1 (Fig. 20), use alignment aperture AA1 for vertcal adjustment and AA2 for horizontal adjustment (Appendix D), BW1 BS OPO Xtal DP SP SM PD2 Fig Adjust M1 through the alignment aperture (and the dispersion block(s)) to center spot on M2/ OC (Fig. 21) BW1 BS OPO Xtal DP SP SM PD2 Fig. 22 OPO PP Auto Manual # September 2008

31 - Place the moveable aperture between M2 and M1, so that the inicent beam passes through a hole, - Adjust M2/OC to overlap the retroreflection from M2/OC with the incident beam (Fig. 24) first on position 1 then on position 2, BW1 BS OPO Xtal DP SP SM PD2 Fig Use CM1 to center the spot of the reflectored beam on M4 (block and unblock the bean between M1 and M2/OC to make sure that it is the reflectored beam). Use alignment aperture AA1 for vertical adjustment and AA2 for horizontal adjustment, - Place the moveable alignment aperture AA1 between M4 and CM1, so that the incident beam passes through a hole, BW1 BS DP SP SM PD2 Fig Adjust M4 to overlap the retroreflection from M4 with the incident beam (Fig. 24), OPO PP Auto Manual # September 2008

32 BW1 BS OPO Xtal DP SP SM PD2 Fig Place the moveable aperture in front of M2/OC that the blue beam passes the aperture, then align the spot of the 2nd round trip with M4 (Fig. 25), - When the spots of the 1 st and 2 nd round-trip are overlapping, remove the alignment aperture, (if necessary replace the dispersion plates and / or set the pump laser to the proper wavelength) - Change cavity length slowly using the cavity length adjusting knob until visible light is flashing, check with a paper behind M1. It indicates the OPO generation, - Optimize the OPO operation for output power and mode structure by cavity mirror and length alignment, lens and crystal position and careful pump wavelength tuning. The bandwidth is strongly dependent on the crystal position between CM1 and CM2 but the pulse length does not change. Thus for optimum time-bandwidth find the maximum power position of the crystal and move the crystal towards CM1 until you loose approximately 10% of output power. The spectrum should become narrower. - If necessary (no spectrum on the screen), optimize the spectrometer input using BS and SM (see Chapter 7.3.) Proceed as described in Chapter OPO PP Auto Manual # September 2008

33 Ring OPO Fig axis SHG- crystal mount with heater / cooler unit (left) and SHG (or dummy) crystal holder (right), (1) horizontal x-translation micrometer screw, (2) crystal holder fixing screw, (3) crystal height, (4,5) crystal angle tilt adjustment screws, (6) crystal holder with temperature sensor including a 6 mm or 20 mm (fs or ps) SHG crystal, (7) thermo sensor, (8) thermo sensor plugged into socket The SHG crystal is temperature tuned from 0 to 200 C. Therefore the crystal needs to be either cooled by a TEC or heated. The crystal is mounted directly on the heater, the cooler (TEC) is automatically motor driven onto the SHG-crystal if necessary. Clean the SHG crystal (with methanol) and place the crystal holder into its mount as shown in Fig. 23. Make sure the golden connectors of the crystal holders fit into the golden sockets of the mount. Tighten the SHG crystal with the 2 mounting screws (2). Connect the temperature sensor and make sure, the electrical cables and the water lines are connected with the sockets in the base plate (see Chapter 3.2.). Water must be connected to the OPO (in line with the Laser). Without water flow the heater / cooler unit will be disabled. Set the micrometer screw (1) to the position given in the test report, adjust the crystal height (3) and align the horizontal and vertical tilt angle (4,5) parallel to the base plate. The SHG-crystal is hygroscopic: keep the crystal in a dry place if not used and purge the OPO with dry air or nitrogen! Caution: When heated, the housing of the oven becomes hot! The heater / cooler unit will be deactivated if no water flow is detected! When running the cooler below room temperature the OPO is to be purged with dry air or N2 to avoid water condensation or icing on the SHG crystal. OPO PP Auto Manual # September 2008

34 BW1 A2 DP OPO Xtal M4 BW2 SHG Xtal M2/OC K Fig. 27 Ring SHG OPO - Make sure to set the Ring cavity configuration (chapter 4.2.), mount the appropriate crystals and dispersion plates / set up the mirror distances according to pump laser repetition rate and pulse duration, - Set the OPO crystal perpendicular to the pump beam by using the back reflection and an IR viewer (use 4 and 5 in Fig. 10), mode locking could break down and thus the SHG-spot is fluctuating. - Place a sheet of fluorescent paper in front of M2/OC, to block the SHG-Spot in forward direction, - For crystals with required pump wavelength of 800 nm and below: The dispersion blocks inside the cavity do not transmit wavelength below 400 nm. Tune the pump laser above 820 to transmit the blue SHG spot through the dispersion plates, OPO PP Auto Manual # September 2008

35 BW1 SHG Xtal DP OPO Xtal M2/OC BW2 PD3 BW3 Fig Use the backward reflection and adjust CM1 through the to center spot on M4. Use alignment aperture AA1 for vertical adjustment and AA2 for horizontal adjustment, BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig Adjust M4 to center spot on M3 (Fig. 29). Use alignment aperture AA1 for vertical adjustment and AA3 for horizontal adjustment, BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig. 30 OPO PP Auto Manual # September 2008

36 - Tilt the OPO-crystal vertically to move the back reflection of the crystal down on aperture A1 until the back reflection hits the lens holder L1. - Remove the papersheet in front of M2/OC, - Use the blue spot in forward direction and adjust CM2 to center the blue spot on M1 (Fig. 30). Use alignment aperture AA1 for vertical adjustment and AA2 for horizontal adjustment, BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig Adjust M1 through the dispersion plate(s) and the alignment aperture AA1 to center spot on M2 (Fig. 31), BW1 2 SHG Xtal 1 DP OPO Xtal M2/OC BW2 PD3 BW3 Fig Adjust M2 through the alignment aperture AA1 to center spot on CM3 (Fig. 32), BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig. 33 OPO PP Auto Manual # September 2008

37 - Adjust CM3 through the alignment aperture AA1 to center the blue spot on CM4 (Fig. 33), check pass through crystal SHG-crystal, BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig Adjust CM4 to center the blue spot on M3 (Fig. 34). Use alignment aperture AA1 for vertical adjustment and AA2 for horizontal adjustment, BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig Adjust M3 through the dispersion plate(s) to center the blue spot on M4 (Fig. 35). Use alignment aperture AA1 for vertical adjustment and AA2 for horizontal adjustment, BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig. 36 OPO PP Auto Manual # September 2008

38 - Place AA1 in front of M2 (do not block beam to CM3!) and adjust M4 to bring the blue spot a second time on M1, - Adjust only M4 to overlap the first and the second blue spot on the aperture (Fig. 36), BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig Place the aperture AA1 between M1 and CM2 (Fig. 37) and overlap the blue spots from the first and second round trip by adjusting M3 only, - Repeat the last three steps in an iterative procedure a few times until a good overlap at both positions of the aperture is achieved, - Change cavity length slowly using the cavity length adjusting knob (K in Fig. 9) until visible light is flashing OPO Optimization - Connect control electronics to optics with the 25 pins-sub-d cable for the sensor modules and the BNC/ SMA cable for the piezo voltage, connect the 7 pin round / 9 pin Sub-D for Ring systems. Then switch on the OPO electronics. - Display the piezo voltage as bar graph by pushing UTILITY MENU, DISPLAY OPO, BARGRAPH U -PIEZO, - Set the piezo voltage with TUNING - knob to approx. 50% of the maximum value, - Compensate this length detuning by shifting M2/OC manually with the translation element (K in Fig. 9) until the OPO is generating again, - Align the OPO cavity with the mirrors M1 and M4 to an optimal mode structure and maximum power, - Use SM1 and SM2 to direct the deflected beam from beam splitter SM1 into the spectrometer (internal spectrometer version). For a set up with external spectrometer, use the delivered beam splitter / mirror to direct the IR-signal for IR-operation and the VIS-signal for VIS-SHG operation into the spectrometer. Use the visible mixing products as alignment help. Set the SPECTROMETER GAIN and the ZOOM range to maximum. Align and optimize the beam into the spectrometer, reduce the SPECTROMETER GAIN if necessary. OPO PP Auto Manual # September 2008

39 - Set the OPO to the desired wavelength range (+/- 50 nm) and optimize for maximum power and bandwidth. - Maximize OPO output power and optimize spectral bandwidth with crystal and lens position (for Ring OPO: also the SHG-crystal position) and mirror alignment under continuous control of mode structure of the reflected beam. The bandwidth is strongly dependent on the crystal position between CM1 and CM2 but the pulse length does not change. Thus for optimum timebandwidth find the maximum power position of the crystal and move the crystal towards CM1 until you loose approximately 10% of output power. The spectrum should become narrower (only needs to be done at first installation or configuration changes, please refer to the installation protocol). - For best time-bandwidth product the use of the proper dispersion plate is essential (see Appendix A) Ring to Linear Conversion - Loose the screw in front of M4 and flip mirror mount M4 to the position perpendicular to the beam from CM1, set the approciate OC at position M2/OC, - Tilt mirror mount M2/OC that it is retro-reflecting the beam from M1, - Mount the approciate dispersion plate for Linear OPO and respective pulse length (see test protocol and Appendix A), - Put the mirror mount M2/OC to the approciate position (see test protocaol) as described in chapter 5.1., - Align this cavity as described in chapter 5.3., - The IR signal beam is then coupled out through window BW Linear to Ring Conversion - Replace the output coupler OC at position M2/OC by the approciate mirror (see test protocol and Appendix A), - Flip mirror mount M4 to a position parallel to the OPO front panel (Fig. 9) and tilt mirror mount M2 that it is reflecting the beam from CM1 to M3, - Put the mirror mount M2/OC to the approciate position (see test protocol) as described in chapter 5.1., - Mount the appropriate dispersion plates for the respective pulse length (fs, ps)(see test protocol and Appendix A), - Align this cavity as described in chapter 7.2, but notice the modification that the beams has not to be overlapped when returned (retroreflection) from M1 and M4 but after a complete cavity round trip only, - After phase matching the SHG-crystal (see chapter 1.4.) the VIS SHG-signal is coupled out through mirror CM4/L2 and window BW3, - For IR generation in the ring cavity use the respective OC at position M2/OC and use the dummy crystal instead of the SHG crystal. OPO PP Auto Manual # September 2008

40 Picosecond and Femtosecond Configuration Conversion - For a conversion put your laser to the respective time regime, close aperture A1 and exchange the OPO crystal (fs 2mm long, ps 6 mm), - Install the isolator for ps-operation. Remove it for fs-operation, - Change distance between mirrors CM1 and CM2 by moving CM2, - for fs to ps operation + 2 mm (distance 118 mm, move all 3 screws of CM2 eight turns counter-clockwise), - for ps to fs operation - 2 mm (distance 116 mm, move all 3 of CM2screws eight turns clockwise). - Exchange the necessary dispersion plates (see Appendix A). Linear configuration: - Centre the crystal to the middle of CM1 and CM2, - Exchange fs/ps output coupler (if supplied, depending on system configuration) (see Appendix A), - Set the OPO cavity length to a value equivalent to the new pump laser cavity length (frequency counter + test protocol) and align the OPO as described in chapter 7.1. or 9, - Get the OPO running, adjust crystal and lens positions and correct distance CM1-CM2 for maximum output power. Ring configuration only: - Go to linear configuration, change and optimize the time regime for linear configuration and proceed as described above, - Change distance between mirrors CM3 and CM4 (for fs- operation to 104 mm, for ps-operation to 109 mm) as follows, - Unscrew the foot of the CM3 mirror from the base plate and use the two other mounting holes on the mount / base plate: for ps-operation the 2 screws of the CM3 foot are aligned parallel to the front face, for fs-operation perpendicular, - Check for the right distance between CM3 and CM4, fine adjust with the 3 alignment screws of CM3, - Exchange the SHG-crystal, - Set the OPO cavity length to a value equivalent to the new pump laser cavity length (frequency counter + test protocol), - Centre the SHG-crystal to the middle between both mirrors, align the OPO for Ring configuration (see linear to Ring conversion 7.2), get the OPO running, set the appropriate phase matching temperature and adjust the crystal position for maximum output power. OPO PP Auto Manual # September 2008

41 5.4. Activation of Stabilization Unit - Check that the proper configuration is set in the controller (fs-ir, ps-ir, fs-vis, ps-vis, see UTILITY MENU --> CONFIG) - Set the desired wavelength via the controller (or RS232): OPO MENU SET LAMBDA with the blue rotary knob. Then press ACTIVATE. The piezo voltage will be changed and therefore the length of the OPO cavity to tune to the set wavelength while comparing with the measured central wavelength. If the set wavelength is reached, a green square is displayed beside the set wavelength (and a success signal is given to the RS232 if the set command came via RS232). - With the HYSTERESIS settings one can set a wavelength range (+/- λ), in which the controller does not correct the wavelength and stays stand-by. This is to improve stability, because small wavelength fluctuations could come from measurement errors such as noise and a small jitter in the spectrometer. A setting of approx to 1 nm for fs-operation and app. 0.3 nm for psoperation is recommended. Failure of locking: If after approx. 40 sec. the set wavelength has not been reached yet, the system locks out again and goes into manual mode. Several points should be checked: 1. The piezo voltage is at the end of its range: Set the piezo voltage to approx. 50%, change the cavity length manually until the approximate set wavelength is reached and try again. 2. The desired wavelength is in a water absorption region (especially between 1340 nm and 1480 nm): Purge the system with nitrogen or dry air. 3. The set wavelength is outside the accessible tuning range when changing the cavity length: go to the nearest wavelength possible) and realign the mirrors for maximum power and try again. If this does not help (especially in ps-operation), change the pump wavelength by a few nm, go down for lower wavelength and vice versa. If the wavelength is outside the specified spectral range for this crystal, you can exchange the PP-crystal (optional, see crystal specifications chapter 1.6.). 4. If the locking is unstable or too slow please check if the controller is set to the proper configuration, i.e. fs-ir, ps-ir, fs-vis or ps-vis (OPO MENU --> CONFIG) 5. In the VIS-SHG mode please check LBO temperature for optimum SHG generation at the desired wavelength. OPO PP Auto Manual # September 2008

42 6. Fast Alignment Routine for an Installed System (daily routine) - In case the cavity length is nearly exactly known and all distances are optimized (lens and crystal position), the cavity can be aligned without the YAG laser easily, - Place a sheet of white paper in front of M2/OC, - Tune the pump laser to a wavelength that optimizes the visibility of the blue SHG-spot Linear OPO Use these blue spots to align the cavity according to the method described in the last part of chapter 5.3. such as: - if pump wavelength is below 800 nm, take out the dispersion block(s) or tune pump laser to >820 nm, BW1 BS OPO Xtal 2. DP 1. SP SM PD2 Fig Place the moveable aperture between M2 and M1, - Adjust M2/OC to overlap the retroreflection from M2/OC with the incident beam (Fig. 38), BW1 BS OPO Xtal DP SP SM PD2 Fig Place the moveable aperture in front of M2/OC that the blue beam passes the aperture, then align the spot of the 2nd round trip with M4 (Fig. 39), OPO PP Auto Manual # September 2008

43 - When the 1 st and 2 nd round trip are overlapping, remove the alignment aperture, (if necessary replace the dispersion plates and / or set the pump laser to the proper wavelength), - Change cavity length slowly until visible light is flashing, check with a paper behind M1. It indicates the OPO generation, - Optimize the OPO operation for output power and mode structure by cavity mirror and length alignment, and careful pump wavelength tuning. Proceed as described in Chapter Ring OPO - If the pump wavelength is below 800 nm, tune pump laser to >820 nm BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig Place the aperture in front of M2 (do not block beam to CM3!) and adjust M4 to bring the blue spot through CM1 and CM2 a second time on M1, - Adjust only M4 to overlap the first and the second blue spot on the aperture (Fig. 40), BW1 DP OPO Xtal BW2 SHG Xtal M2/OC PD3 BW3 Fig Place the aperture between M1 and CM2 (Fig. 41) and overlap the blue spots from the first and second round trip by adjusting M3 only, - Repeat the last three steps in an iterative procedure a few times until a good overlap at both positions of the aperture is achieved, - Go back to the proper pump wavelength if necessary and change cavity length slowly until visible light is flashing. OPO PP Auto Manual # September 2008

44 7. Laser Spectrometer WaveScan 7.1. Specifications Wavelength range nm for IR OPOs, nm for VIS+IR OPOs Bandpass.... ~ 0.2 nm Wavelength accuracy.. ± 0,1 nm Measuring rate... up to 6 spectra per second Dynamic range bit A/D converter, 6 gain ranges separated by factor Technical Description The WaveScan is basically a grating spectrometer with nearly Littrow configuration and a focal length of 200 mm. The grating rotates with a rate of about 6 rounds per second; the diffracted laser light is focussed on the exit slit. For signal detection a fast photodiode behind the exit slit is applied. Different spectral versions of the WaveScan are available which have different photo detectors: InGaAs or combined Si/InGaAs, depending on the version. At a distinct angle position of the grating a high precision trigger starts the measurement. Following that a fixed number of data points (up to about 35000) are taken with a sampling rate of about 1.3 MHz. These data points are correlated to the wavelength values according to the internal calibration and are graphically displayed on the screen. OPO PP Auto Manual # September 2008

45 7.3. Set-up Internal spectrometers: BS Spectrometer SM Fig. 42 Internal spectrometer with beam splitter window BS and steering mirror SM - After the OPO is generating, use the beam splitter BS and the steering mirror SM to direct the beam centrally onto the centre of the focussing lens. (You can use the visible mixing products as alignment help. Attention: they are not completely collinear with the IR signal.) With middle position of the focussing lens now the beam should be focussed on the centre of the entrance slit. Otherwise correct with walking the beam with BS and SM. If aligned correctly, a line due to an internal reflection of the laser beam should appear on the alignment window at the top panel of the optics. This line should be at half height on the window. - It is recommended to watch the signal on the display of the control electronics in the biggest zoom window (full wavelength range) and maximum gain. For operation instructions see the respective chapters of this manual. As soon as a measuring signal (laser line in the spectrum) is to be seen, maximize it by fine adjustment of BS and SM. OPO PP Auto Manual # September 2008

46 External spectrometers Fig. 43 External WaveScan Laserspectrometer Mounting the Alignment Tripod If you use the WaveScan to measure a free travelling laser beam it is of advantage to use the enclosed alignment tripod. It consists of two arms with adjustment screws. Assemble the two arms so that the two arrow marks are placed opposite to each other and fix the connection with the screw. Then mount the tripod at the base plate of the spectrometer optics. Connecting the Spectrometer - Connect the spectrometer optics with the respective connector (SPECTR) to the rear panel of the control electronics using the enclosed 15-pin Sub-D interconnection cable. Connect the control electronics with the electrical outlet by the enclosed power cord. - Caution! Connect or disconnect the spectrometer optics only with the electronics switched off. Otherwise the device might be seriously damaged. Alignment - Warning! All alignments should first be done with attenuated laser beam! Pay attention to possible back reflections from the focussing lens or the beam entrance! - Switch on the control electronic unit with the power switch. - Use the delivered beam splitter and position the WaveScan optics parallel to the reflected beam as good as possible. Direct the beam to the centre of the focussing lens. (You can use the visible mixing products as alignment help. Attention: they are not completely collinear with the IR signal.) With middle position of the focussing lens adjustment screws now the beam should be focussed on the centre of the entrance slit. Otherwise correct for the alignment of the whole OPO PP Auto Manual # September 2008

47 optics module by horizontal and vertical displacement and angle tuning. Use the alignment screws of the tripod and fix them with the counter nut! If aligned correctly, a line due to an internal reflection of the laser beam should appear on the alignment window at the side panel of the optics. This line should be at half height on the window. Use the adjustment screws of the focussing lens for fine adjustment. - It is recommended to watch the signal on the display of the control electronics in the biggest zoom window (full wavelength range) and maximum gain. For operation instructions see the respective chapters of this manual. As soon as a measuring signal (laser line) is to be seen, maximize it by fine adjustment of the optics unit. - Tighten the jam nuts of the tripod for stable and jitter free operation of the spectrometer Handling The WaveScan allows for a wavelength-calibrated display of the measured spectrum on the integrated LCD screen of the OPO electronics, saving this spectrum and later displaying it, changing the displayed wavelength range (ZOOM), displaying cursors for the x- and y-axis, and automatic display of the peak wavelength and the half width of the laser line. Most of the settings are done by activating the respective parameter with the buttons on the front panel and in the SPECTRUM MENU. Here the functions of the menu buttons next to the screen are defined by soft menus. You can always directly set the gain by pressing the buttons SPECTROMETER GAIN +/ Starting and Stopping the Measurement The measurement can be stopped at any time by pressing the RUN/STOP button in the SPECTRUM MENU. The message SYSTEM STOPPED! will appear in the display and the last measured spectrum will be shown. By pressing the RUN/STOP button again you can restart the measurement GAIN The WaveScan has 6 gain levels which can be set according to the intensity of the measured signal. The gain levels correspond to factors of in the amplifier. Press the buttons SPECTROMETER GAIN + or - to increase or decrease the gain, respectively. The current gain level is displayed in the main menu at bottom left position (SGAIN: xxx). Note: an offset of the displayed spectrum for each gain setting can be added by choosing the SPEC OFFSET submenu in the SPECTROMETER MENU menu. With the buttons OFFSET +/- the offset can be changed. OPO PP Auto Manual # September 2008

48 CURSORS Two x-axis (wavelength) cursors and two y-axis (relative intensity) cursors can be displayed in the spectral graph. With these cursors significant points in the measured spectrum can be marked and their wavelength and relative intensity can be determined. The cursors are displayed in green color. Together with each of the x-axis cursors the respective wavelength is displayed in red color. The difference value of them will be displayed as. With the y-axis cursors additionally a middle line at half the distance between them is displayed. Operation: To activate the cursors for the x- and y-axis the CURSOR button below the screen has to be pressed. The cursors can be moved to every desired point of the spectrum by activating the respective cursor HOR1 to VERT2 in SPEC CURSOR (activated cursor is highlighted) and moved with the black rotary knob directly below the screen. There is an additional line between the two horizontal cursors at half height to ease half width measurements. The corresponding wavelengths values of the x-cursors and the difference in nanometers are shown on the screen in green color and denoted as. Please note: the bigger the zoom factor of the display the more accurate the setting of the cursors DISPLAY You can select different display options for the spectrometer in the spectrometer display menu (UTILITY MENU DISPLAY SPEC). By pressing the SPECTRUM, CENTRAL WAVELENGTH; PEAK WAVELENGTH or FWHM buttons, the spectrometer graph, the measured peak wavelength, and the FWHM of the peak can be switched on or off respectively ZOOM By pressing the ZOOM IN / OUT buttons in the SPECTRUM MENU the displayed spectral range can be changed from 10 nm to maximum in 6 steps. The zoom window is always centered around the green cursor, which is activated with the WINDOW SPECTRUM option in the CURSOR menu. The zoom window can be shifted by moving the cursor with the black rotary knob in the CURSOR Menu. In the top line of the display the position of the cursor, the left and the right margins are shown in red. Please note: When changing the displayed spectral range only the resolution of the display is changing. The detection of the central wavelength and the FWHM is not affected by it SMOOTH a Spectrum If a spectrum is noisy, the noise can be reduced by pressing the button SMOOTH in the SPECTRUM. It then averages over 4 adjacent wavelength data points to reduce the noise. The resolution will be reduced by 0.1 nm independent of the chosen Zoom range. OPO PP Auto Manual # September 2008

49 7.5. How can I stop a measurement? By pressing the RUN/STOP button in the SPECTRUM MENU the measurement can be stopped and restarted at any time. This is a comfortable way of inspecting a spectrum and doing measurements on it.... set the displayed wavelength range? By pressing the ZOOM IN / OUT buttons in the SPECTRUM MENU the displayed spectral range can be changed from 10 nm to 500 nm in 5 steps. The zoom window is always centered around the green cursor, which is activated with the WINDOW SPECTRUM option in the CURSOR menu. The zoom window can be shifted by moving the cursor with the < and > buttons. In the top line of the display the position of the cursor, the left and the right margins are shown in red.... determine the wavelength? There are different methods to determine a wavelength with the WaveScan. 1. The central wavelength of the global maximum in the spectrum is displayed automatically if the function UTILITY MENU DISPLAY SPEC LAMBDA CENTRAL is set ON. 2. The peak wavelength of the global maximum in the spectrum is displayed automatically if the function UTILITY MENU DISPLAY SPEC LAMBDA PEAK is set ON. 3. The cursors for the x- and y-axis can be activated by pressing the CURSOR button in the spectrometer menu. The cursors can be moved to every desired point of the spectrum by activating the respective cursor in the menu (activated cursor: thick green line) and moved with the < and > buttons. There is an additional line between the two horizontal cursors at half height to ease half width measurements. The corresponding wavelength values of the x-cursors and the difference in nanometers are shown on the screen instead of the automatic peak detect data. Please note: the bigger the zoom factor of the display the more accurate the setting of the cursors.... increase sensitivity? With the buttons SPECTROMETER GAIN + and - the amplifier gain level can be set in steps. The set value is displayed in the main menu (bottom right).... monitor the pump wavelength? Go to SPECTRUM MENU SPECMODE PUMP and the sensitive spectral range changes from nm to nm. In the top line λ pump will be displayed in red. There will be always a fraction of the pump beam reflected into the spectrometer. This function needs to be switched off when operating the OPO for monitoring and stabilization of the signal wavelength. OPO PP Auto Manual # September 2008

50 8. Troubleshooting Multiple Back Reflections from Output Coupler When adjusting the back reflection (either SHG or Ti:Sa NIR spot) from the output coupler (OC) often more than one back reflection is to be seen. This is due to reflections from front and back side and the wedge in the OC. The coating of the front and back surfaces of the OC are optimized for the OPO wavelength but not for the pump wavelength and the SHG of the pump. Thus these reflections can occur with undefined intensities. Fig. 44 Back reflection If you can see only 2 back reflections (one from the front and one from the back surface of the OC), they may have similar intensities. Even if one of them is more intense it may not be the correct reflection from the front surface of the OC. Thus try to find a third reflection, which is rather weak. This reflection (3) is created by three internal reflections in the OC and therefore much weaker than reflections 1 and 2 which are only reflected by an OC surface once. If you found reflection No. 3, reflection No. 1 (see Fig. 44) is the reflection from the front surface. This one you need to use to adjust the OPO. If there is no generation, please check: - Pump beam position at aperture A1, A2, small aperture in front of lens L1, - Is the right crystal in the beam, 2 mm for fs, 6 mm for ps, - Is the pump wavelength in the necessary range (PP775 pumped around 775 nm, PP830 pumped around 830 nm), - Is the pump laser modelocked, - Is the cavity length in the right range (compare laser repetition rate to OC position given in data sheet, see Chapter 6), do you have the proper dispersion plates inserted? Check mirror position on translation stage, - Are the mirrors mounted in the proper direction (coating, marked with an arrow or triangle, to the beam), OPO PP Auto Manual # September 2008

51 - Does the distance between CM1 and CM2 fit the current pump pulse duration (ps or fs), - Are the crystal and the lens positions correct (see values in test sheet). If there is no Power signal display, please check: - Does the reflection from the output mirror hit the power sensor? (For IR-power sensor: correct with the steering mirror; for VIS sensor: loose the fixing screws and move the sensor slightly.) - Are the power sensors connected with the proper socket on the distribution board? - Is the Gain knob on the distribution board set to a proper value? - Is the Power signal activated in the OPO DISPLAY menu? The wavelength is not stable: - Is the current OPO configuration (i.e. fs-ir, fs-vis, ps-ir, ps-vis) set under UTILITY MENU CONFIG? - Is the OPO purged with nitrogen / dry air? Especially important when working in the wavelength range between 1330 nm and 1480 nm due to strong water absorption lines. Check the humidity. The SHG-crystal can not be heated / cooled - Is the current OPO configuration (i.e. fs-vis or ps-vis) set under UTILITY MENU CONFIG? If not, the heater / cooler is deactivated. - Is the water connected to the OPO? Does the water flow detection wheel rotate? Check for air bubbles! If no water flow is detected, the heater / cooler will be deactivated, a message will be shown on the screen and the red LED on the distribution board in the OPO is illuminated. The spectral bandwidth is too broad: - Try to improve the spectral bandwidth: - Optimize crystal position with the micrometer screw between CM1 and CM2, align crystal and lens position for maximum power, then move crystal towards CM1 to 90% of maximum power. - Change of pump wavelength (especially sensitive in ps mode), tune the pump laser a few nm towards longer wavelength - Realignment with M1 and M4, trying to maintain power by getting smaller bandwidth The desired wavelength can not be reached: - slightly adjust pump wavelength, set the OPO to the closest wavelength achievable and realign OPO with M1 / M4 for maximum power, then tune the OPO further. Shorter OPO wavelength require shorter pump wavelength. For longer OPO wavelength apply longer pump wavelength. Please refer to the test protocol. OPO PP Auto Manual # September 2008

52 9. Theory of Optical Parametric Conversion and the PP Automatic OPO An OPO uses a nonlinear gain medium with a large second order susceptibility, χ 2, to convert a pump photon of high energy into two photons of lower energy. The parametric process is possible with CW, pulsed, or ultrafast pump sources and is peak power dependent. With the advent of reliable, high-powered mode locked oscillators and high quality nonlinear crystals, optical parametric oscillators (OPOs) are viable sources of widely tunable ultrafast light. The below is a short review of the physics of an optical parametric process. The optical parametric down conversion process converts an input pump wave into two outputs, the signal and idler. For efficient energy transfer it is necessary that all three waves remain in phase, i.e., all three waves must propagate through the crystal at the same velocity. This implies that the index of refraction of the three waves is the same. Unfortunately, under most conditions, the normal dispersion of a crystal is such that the indices are different for the pump, signal, and idler beams. Luckily, dispersion can be offset by using the natural birefringence of uniaxial or biaxial crystals. These crystals have two refractive indices for a given direction of propagation, corresponding to the two allowed orthogonally polarized modes. By an appropriate choice of polarization and direction of propagation it is often possible to minimize the phase mismatch and even theoretically approach a zero mismatch. This is obviously termed phase-matching (or to a lesser extent index matching). Phase-matching In general there are two distinct types of phase-matching or techniques to satisfy the momentum conservation requirements. These techniques are referred to as type I (or parallel) and type II (or orthogonal) phase matching. The type of phase matching that is exploited depends on the crystalline structure and the orientation of the crystal with respect to the pump beam. In type I phase-matching, the polarization vectors of the signal and idler are parallel and orthogonal to that of the pump. Whereas in the type II process the polarization vectors of the signal and idler are perpendicular to each other and the pump polarization vector is parallel to the signal or idler polarization vector. Moreover, when the propagation direction is along one of the principle axes of a crystal (such as the optic axis in a uniaxial, birefringent crystal), the phase-matching is termed noncritical, while for any other direction it is referred to as critical phase-matching. In general, noncritical phase matching has a wider acceptance angle which makes the process insensitive to small alignment deviations, insensitive to small temperature changes, and allows for the use of longer crystals which result in a higher conversion efficiency. The above brief description leaves open the possibility of complete conversion of the fundamental beam to the signal and idler beam. In practice this is never realized. The conversion is limited by the pump beam divergence, the bandwidth of the pump beam, by angular and thermal deviations from the ideal phase-matching conditions, various nonlinear and saturation processes, and by a back conversion of the signal and idler to the pump. By convention, the signal is defined by the higher frequency (shorter wavelength) of the two generated outputs. The frequency separating the signal and idler is called the degeneracy point OPO PP Auto Manual # September 2008

53 and occurs at twice the pump wavelength. These frequencies must obey the following energy (or frequency or wavelength) and momentum conversation relations: υ p = υ s + υ i.... eq. 1 n p υ p = n s υ s + n i υ i,.. eq. 2 Where υ refers to a frequency, n refers to an index of refraction, and the subscripts refer to pump, signal, and idler. It is often convenient to express eq. 1 in terms of the wavelength (λ) of the three beams: 1/λ p = 1/λ s + 1/λ i... eq. 3 Periodically Poled Systems In addition to the energy and momentum relations, the OPO crystal must have a high gain, wavelength accessibility, high quality, high reliability, and availability. A relatively new process, called periodic poling, can be used on many bulk crystals (KTP, RTP and LBO) to achieve or enhance some of these desired qualities. Recall that if the wavelengths of the pump and generated beams begin to become out of phase, the signal and idler will no longer build-up in intensity and can actually begin to decrease in intensity. In conventional birefringent phase matching the natural birefringence of the crystal is used to compensate for the wavelength dependence of the index of refraction. Unfortunately, being forced to use the particular configurations defined by these phase matching techniques often confines us to crystallographic orientations that do not exploit the highest nonlinear coefficients. Periodically poled crystals employ a completely different technique to minimize the phase mismatch and can be used on any crystalline configuration. This technique is called quasi-phase matching (QPM). And, unlike in the bulk crystal phase matching techniques, all three waves have the same polarization. A periodically poled crystal begins as a bulk crystal. This crystal is then modified to consist of alternating thin strips of the same crystal but oppositely poled. This modification is accomplished by first using microelectronic techniques to deposit thin electrodes on the crystal. A high voltage field is then applied to pole the material (2-3 KV for KTP and up to 11 KV for LN). The electrodes are then removed. The result is a material that has a periodic poling of the permanent electric dipole. This results in an effective second order susceptibility, χ 2, that has a constant amplitude but a sign that is reversed in each domain. The width of the poled domains is carefully selected. It is the distance that is required for the phase of the pump beam to rotate 180 degrees with respect to the signal or idler beam. The reversal of the sign of χ 2 has the effect of flipping the phase of the pump wavelength 180 degrees and thus brings it right back into phase with either the signal or idler. This leads to a modified phase matching condition from equation (2): n p υ p = n s υ s + n i υ I +1/Λ.. eq. 4 OPO PP Auto Manual # September 2008

54 with Λ as the poling period. It follows, that by varying the poling period of periodically poled crystals, nonlinear crystals with customized properties can be designed. Quasi-phase matching has many advantages. Periodically poled crystals can be designed to exploit the nonlinear coefficients of any crystalline orientation. This could result in higher conversion efficiency. But often the conversion efficiency is limited by the pump beam divergence, the finite bandwidth of the pump beam, and ultimately by the dispersion of the light beams involved in the three-wave interaction. QPM also simulates a non-critical phase matched condition that makes the OPO insensitive to angular deviations or temperature fluctuations. In addition to this flexibility, the unique properties of a periodically poled crystal make it possible for a single pump wavelength to satisfy the above conservation equations for over hundreds of nanometers of bandwidth of a signal wavelength. Tuning of Periodically Poled OPOs The momentum and energy conservation requirements are simultaneously fulfilled for hundreds of nanometers of a signal wavelength in a periodically poled crystal. But in order for the parametric process to occur, the power levels must be high enough to reach a minimum threshold. In synchronously pumped OPOs the threshold is reached by having the resonant pulse (in our case the OPO signal pulse) and the pump pulse present in the crystal at the same time. This is possible if the optical path lengths of the pump source and OPO are matched. The optical path length is determined by the time it takes for a light pulse to make a single round trip within the optical cavity. PP crystals do have an extremely broad phase matching bandwidth, thus PP-OPOs can generate a broad wavelength range with a fixed pump frequency. They are either tuned by intracavity gratings, birefringent filters or by cavity length detuning using the intrinsic GVD of the crystal. This effect occurs because the cavity round-trip time for the signal pulse depends on wavelength through the contribution of the group velocity inside the crystal. The last method is by far the most elegant one, because it is simple and allows for fast tuning. To enhance the effect an intracavity block of a heavy flint glass is added as an additional dispersion element. Thus the broad phase matching bandwidth is still maintained with suitable short PPcrystals while the additional group velocity dispersion is leading to well separated spectra with nearly transform limited pulses which are easily tunable by cavity length detuning. The dispersion of the intracavity dispersion element is such that every wavelength propagates through the crystal at a different velocity. And since the time in the crystal is part of the round trip duration, every wavelength requires a slightly different physical cavity length to achieve synchronization which is necessary to reach the parametric process threshold. This is exploited as a means to tune a periodically poled OPO. OPO PP Auto Manual # September 2008

55 Appendix A: Lists of OPO Mirrors, Dispersion Blocks and Crystalls... fs Linear ps Linear fs Ring ps Ring...59 OPO PP Auto Manual # September 2008

56 fs Linear L1 CM1 CM2 L Idler Pump In OPO Xtal depl pump Idler Out dispersion plate M2/OC M4 M1 IR Out Spectrometer CM1 OPO Xtal CM2 M1 M2/OC M4 distance dispersion CM1-CM2 plate low power (λ pump <0.6 W) S-P100 pp (fs) S-P125 S-C OC-S3 S-C standard S-P100 pp (fs) S-P125 S-C OC-S4 S-C high power (λ pump > 2 W) S-P100 pp (fs) S-P150 S-C OC-S4 S-C Idler option: low power(λ pump <0.6 W) S-P100 pp (fs) S-I125 S-C OC-S3 S-C standard, idler S-P100 pp (fs) S-I125 S-C OC-S4 S-C high power(λ pump > 2 W) S-P100 pp (fs) S-I150 S-C OC-S4 S-C OPO PP Auto Manual # September 2008

57 ps Linear isolator L1 CM1 CM2 L Idler Pump In OPO Xtal depl pump Idler Out dispersion plate M2/OC M4 M1 IR Out Spectrometer CM1 OPO Xtal CM2 M1 M2/O2 M4 distance dispersion CM1-CM2 plate low power (λ pump <0.6 W) S-P100 pp (ps) S-P125 S-C OC-S3 S-C standard S-P100 pp (ps) S-P125 S-C OC-S4 S-C high power (λ pump >2 W) S-P100 pp (ps) S-P150 S-C OC-S4 S-C Idler option: low power(λ pump <0.6 W) S-P100 pp (ps) S-I125 S-C OC-S3 S-C standard, idler S-P100 pp (ps) S-I125 S-C OC-S4 S-C high power(λ pump >2 W) S-P100 pp (ps) S-I150 S-C OC-S4 S-C OPO PP Auto Manual # September 2008

58 fs Ring L1 CM1 CM2 L Idler Spectrometer Pump In OPO Xtal dispersion plate M4 (depl pump/ Idler Out) M1 M2/OC M3 SHG Xtal CM4 L2 CM3 (IR Out) VIS Out CM1 OPO Xtal CM2 M1 M2/OC* M4 CM3 SHG Xtal* CM4 M3 distance distance dispersion CM1-CM2 M3-CM4 plate low power (λ pump <0.6 W) S-P100 pp (fs) S-P125 S-C OC-S1 S-C S-SHG SHG LBO (fs) S-SHG S-C standard S-P100 pp (fs) S-P125 S-C OC-S1 S-C S-SHG SHG LBO (fs) S-SHG S-C high power (λ pump > 2 W) S-P100 pp (fs) S-P150 S-C OC-S2 S-C S-SHG SHG LBO (fs) S-SHG S-C Idler option: low power(λ pump <0.6 W) S-P100 pp (fs) S-I125 S-C OC-S1 S-C S-SHG SHG LBO (fs) S-SHG S-C standard, idler S-P100 pp (fs) S-I125 S-C OC-S1 S-C S-SHG SHG LBO (fs) S-SHG S-C high power(λ pump > 2 W) S-P100 pp (fs) S-I150 S-C OC-S2 S-C S-SHG SHG LBO (fs) S-SHG S-C * The Ring OPO can also be used for IR generation by replacing the mirror at M2/OC with the appropriate output coupler (see fs linear list) and the SHG Xtal with a SHG dummy. OPO PP Auto Manual # September 2008

59 ps Ring L1 CM1 CM2 L Idler Spectrometer Pump In OPO Xtal dispersion plate M4 (depl pump/ Idler Out) M1 M2/OC M3 SHG Xtal CM4 L2 CM3 (IR Out) VIS Out CM1 OPO Xtal CM2 M1 M2/OC* M4 CM3 SHG Xtal* CM4 M3 distance distance dispersion CM1-CM2 CM3-CM4 plate low power (λ pump <0.6 W) S-P100 pp (ps) S-P125 S-C OC-S1 S-C S-SHG SHG LBO (ps) S-SHG S-C standard S-P100 pp (ps) S-P125 S-C OC-S1 S-C S-SHG SHG LBO (ps) S-SHG S-C high power (λ pump > 2 W) S-P100 pp (ps) S-P150 S-C OC-S1 S-C S-SHG SHG LBO (ps) S-SHG S-C Idler option: low power(λ pump <0.6 W) S-P100 pp (ps) S-I125 S-C OC-S1 S-C S-SHG SHG LBO (ps) S-SHG S-C standard, idler S-P100 pp (ps) S-I125 S-C OC-S1 S-C S-SHG SHG LBO (ps) S-SHG S-C high power(λ pump > 2 W) S-P100 pp (ps) S-I150 S-C OC-S1 S-C S-SHG SHG LBO (ps) S-SHG S-C * The Ring OPO can also be used for IR generation by replacing the mirror at M2/OC with the appropriate output coupler (see fs linear list) and the SHG Xtal with a SHG dummy. OPO PP Auto Manual # September 2008

60 Appendix B: OPO PP-Automatic - RS232 Command Set RS232 Parameters Baud rate: Data bits: Parity: no Stop bits: Handshake: DTR-CTS Interface cable requirements:... 9pin Sub-D wired 1: OPO Controller... PC TXD..... RXD RXD..... TXD GND.... GND DCD DCD DSR DSR RTS RTS DTR..... DTR CTS CTS 8 OPO PP Auto Manual # September 2008

61 Software Commands Commands from PC to OPO Controller (ASCII characters) SLnnnnn,.. Set OPO wavelength.. nnnnn (ASCII) OPO set wavelength [Angstrom].... response: 2 Bytes (after up to 30 seconds).. (1) 00hex.. FFhex high byte of OPO set wavelength [Angstrom]... (2) 00hex.. FFhex low byte of OPO set wavelength [Angstrom].. If this return value is 0000hex the OPO did not lock at the set wavelength.. within the timeout period. SLQnnnnn, Set OPO wavelength with receive confirmation.. nnnnn (ASCII) OPO set wavelength [Angstrom].... response: 1 Byte (01hex) immediately after receiving the command, Bytes (after up to 30 seconds).. (2) 00hex.. FFhex high byte of OPO set wavelength [Angstrom]... (3) 00hex.. FFhex low byte of OPO set wavelength [Angstrom].. If this return value is 0000hex the OPO did not lock at the set wavelength.. within the timeout period. GH,... Get Humidity.... response: 1 Byte.. (1) 00hex.. FFhex relative humidity [%] GPI,... Get Power IR.... response: 2 Bytes.. (1) 00hex.. FFhex high byte of IR power [arbitrary]... (2) 00hex.. FFhex low byte GPV,... Get Power VIS.... response: 2 Bytes.. (1) 00hex.. FFhex high byte of VIS power [arbitrary]... (2) 00hex.. FFhex low byte GTS,... Get Temperature SHG.... response: 2 Bytes.. (1) 00hex.. FFhex high byte of SHG temperature [degrees centigrade * 10]... (2) 00hex.. FFhex low byte OPO PP Auto Manual # September 2008

62 STSnnnn,... Set SHG temperature.. nnnn (ASCII) SHG temperature set value [degrees centigrade * 10] GZ,... Get Piezo Voltage Pnnnn,.... Set Piezo Voltage nnnn = ASCII SBnnnnnn,... Set Baud Rate.. nnnnnn= ASCII OPO PP Auto Manual # September 2008

63 Spectrometer Commands: GNn,.... Set Spec Gain n = (ASCII) 1 - factor factor factor factor factor factor 300 GG,.... Get spectrometer Gain.... response:.. 1 Byte.. 01hex - factor hex - factor hex - factor hex - factor hex - factor hex - factor 300 LZnnnnn,... Set Zoom Window middle wavelength.. nnnnn (ASCII) middle wavelength of zoom window [Angstrom]..... SZI,.... Zoom In SZO,.... Zoom Out Fn,.... SpecWindow width.. n = ASCII 1 for 5 nm for 10 nm for 20 nm for 50 nm for 100 nm for 200 nm for 500 nm.. SOnnn,... Set Offset... nnn= ASCII Spectrometer offset for the active gain setting Wnnnn,... Spectrum Values.. nnnn= ASCII 256, 512, 1024 for setting of the spectrum data set length GC,.... GETCALIBRATION.... response: 8 Hex values OPO PP Auto Manual # September 2008

64 hex.. FF FF FF FFhex (unsigned long)(k0*1e12) hex.. FF FF FF FFhex (unsigned long)(alpha0*1e9) GSV,.... Get spectral Peak Values.... response: 8 Bytes (1) 00hex.. FFhex high byte of peak wavelength [Ångström] (2) 00hex.. FFhex low byte of peak wavelength [Ångström] (3) 00hex.. FFhex high byte of FWHM [Ångström] (4) 00hex.. FFhex low byte of FWHM [Ångström] If this return value is FFFFhex a spectrometer overflow was detected. (5) 00hex.. FFhex high byte of center wavelength [Ångström] (6) 00hex.. FFhex low byte of center wavelength [Ångström] (7) 00hex.. FFhex high byte of lock state (8) 00hex.. FFhex low byte of lock state lock state:... 1 OPO locked OPO not locked GSH,.... Get Spectrum All.... Response: 2X wavelength values +12 Hex values 00hex.. FFhex high byte 1st value of screen, only Bit 0..3 significant... 00hex.. FFhex low byte 1st value of screen 00hex.. FFhex high byte 256th value of screen, only bit 0..3 significant... 00hex.. FFhex low byte 256th value of screen..... or 512th..... or 1024th... 00hex.. FFhex high byte 1. wavelength (left margin of screen)... 00hex.. FFhex low byte 1. wavelength hex.. FFhex high byte 256th wavelength (right margin of screen)... 00hex.. FFhex low byte 256th wavelength hex.. FFhex high byte Peak wavelength... 00hex.. FFhex low byte Peak wavelength hex.. FFhex high byte Spectrum FWHM... 00hex.. FFhex low byte Spectrum FWHM... OPO PP Auto Manual # September 2008

65 .. 00hex.. FFhex high byte spectrum central wavelength.. 00hex.. FFhex low byte spectrum central wavelength hex.. 00hex.. 01hex OPO LOCK STATUS 0 for unlocked for locked... GSF,... Get Spectrum Fast... Response: 2x wavelength points + 8 Hex values 00hex.. FFhex high byte 1st value of screen, only Bit 0..3 significant.. 00hex.. FFhex low byte 1st value of screen hex.. FFhex high byte 256th value of screen, only bit 0..3 significant.. 00hex.. FFhex low byte 256th value of screen..... or 512th..... or 1024th.. 00hex.. FFhex high byte 1st wavelength (left margin of screen).. 00hex.. FFhex low byte 1st wavelength hex.. FFhex high byte 256th wavelength (right margin of screen) hex.. FFhex low byte 256th wavelength hex.. FFhex high byte Peak wavelength.. 00hex.. FFhex low byte Peak wavelength hex.. FFhex high byte Spectrum FWHM.. 00hex.. FFhex low byte Spectrum FWHM OPO PP Auto Manual # September 2008

66 Correlator commands CAG,.... Correlator Auto Gain.. CAVn,.... Correlator Average.. n = ASCII GA,.... Get Correlator Average.... Response:... 01hex.. 40hex for CFn,.... Correlator Filter.. n = ASCII 0 for off for on GF,.... Get Correlator Filter.... Response:... 00hex for off hex for on CGnnn,... Correlator Gain... nnn = ASCII CPn,.... Correlator Preamp.. n = ASCII 0 for off for on CRn,.... Correlator Range.. n = ASCII 1 for 150 fs for 500 fs for 1.5 ps for 5.0 ps for 15 ps CSn,.... Correlator Smooth.. n = ASCII 0 for off for on GAT,.... Get Correlator FWHM.... Response:... 00hex.. FFhex for 0/ / from scan range GAC,.... Get ACF.... Response: 512 Hex values... 00hex.. FFhex high byte 1st value of ACF 00hex.. C0hex low byte 1st value of ACF only bit 7 and 6 significant hex.. FFhex high byte 256th value of ACF 00hex.. C0hex low byte 256th value of ACF only bit 7 and 6 significant OPO PP Auto Manual # September 2008

67 Appendix C: Exchange of Mirrors in Mount M1 and M4 - Fig. 1 shows the top adjustment gimbal mirror (M1, M4) mount from the back side, mirror, spacer ring, retaining ring and the spanner wrench. - Use the delivered spanner wrench to unscrew the retaining ring at the back side of the mirror mount. Take out the spacer ring and then the mirror. - To place a new mirror into the mount, proceed as above in reverse order. Fig. 1 Gimbal mount OPO PP Auto Manual # September 2008

68 Appendix D: Accessories / Alignment Apertures... for OPO PP Automatic Linear Version additional for OPO PP Automatic Ring Version Alignment Aperture AA Alignment Aperture AA OPO PP Auto Manual # September 2008

69 screws for foot clamps hex keys connector for purging (female/male) mirror key holders for pump mirrors (pump optic set) tubing for purging pump black filter alignment aperture AA2 (for holder M1 and M4) foot clamps alignment aperture AA1 Fig 1. Accessoiries for OPO PP Automatic Linear Version foot clamps for external spectrometer (+ additional srews, not on picture) alignment aperture AA3 (for holder M3) connectors for water cooling (1x female, 3x male) tubing for water cooling Fig. 2 Additional Accessoiries for OPO PP Automatic Ring Version OPO PP Auto Manual # September 2008

70 Fig. 3 Alignment Aperture AA2 in holder M1 or M2 Fig. 4 Alignment Aperture AA3 in holder M3 OPO PP Auto Manual # September 2008