ELECTRONICS FOR PULSE PICKERS

Transcription

1 Rev / ELECTRONICS FOR PULSE PICKERS TABLE OF CONTENTS Description... 2 High voltage switches... 3 Appearance / dimensions... 3 Power ratings... 3 Interfaces... 4 Specifications... 6 How to order?... 6 High voltage power supplies... 7 Interfaces... 7 Specifications... 8 The control board (the control unit)... 9 Appearance / Dimensions... 9 Time diagram and the synchronization Interfaces RS- 232 interface commands desription Photodiode s threshold and triggering Specifications Photodiode assemblies Interfaces Specifications Modifications / How to order? Software... 15

2 DESCRIPTION There is a typical task in the laser industry resampling down the repetition rate of pulsed lasers. Most commonly this task is related to pico- and femtosecond lasers and is known there as pulse picking. Typical seed laser has the repetition rate of tens of MHz (from 10MHz up to 100MHz or even more). For further amplification the repetition rate of tens of khz is needed. As a result some kind of pulse picker is required. The electro- optical crystal like RTP, DKDP or BBO, simply assembled together with the polarizer, and properly driven with the high voltage electronics can select and transmit some of optical pulses from the pulse train and reject all others. E-O crystal polarizer polarizer Controlling and driving electronics In the similar way input/output of pulses into/from the regenerative amplifier may be controlled. E-O crystal Active media HR mirror 1 λ/4 plate polarizer HR mirror The leading edge of electrical pulse (of L/4 voltage) should be applied when the optical pulse is passing through the area 1. The falling edge of electrical pulse applied when the optical pulse is in area 1 again will release the optical pulse from the amplifier.

3 HIGH VOLTAGE SWITCHES The first key element of aforementioned schemes is the high voltage switch capable to produce pulses with very fast rise and fall times. APPEARANCE / DIMENSIONS POWER RATINGS In dependence on the power rating, high voltage switches are available in two different modifications. There are modifications with a) conductive cooling through the bottom and b) water cooling through the internal channels.

4 INTERFACES HV OUTPUT 1,4 HV OUTPUT 1 Pockels cell connections 3,6 HV OUTPUT 2 2,5 N/C - HV INPUT 1,4 (red) HIGH VOLTAGE DC high voltage power supply +4000V DC max 3,6 (blue) HV RETURN DC high voltage power supply return 2,5 N/C - LV INPUT 1,2 (red) LOW VOLTAGE DC low voltage power supply +15V DC 3,4 (blue) LV RETURN DC low voltage power supply return OVERHEAT 1 (yellow) OVERHEAT Signalize about switch s overheating. Normally OVERHEAT loop is opened. In the case of overheating (> 90 C), switch becomes blocked, OVERHEAT loop becomes closed. Max. current capability is 2mA 2 (black) OVERHEAT RETURN Return of OVERHEAT loop

5 INTERFACE 1 (red) PULSE Rising edge of PULSE signal (0-5V step) initiates high voltage pulse at the switch s output. High voltage pulse duration is either defined automatically (when PW JUMPER is on) or coincides with PULSE signal width (when PW JUMPER is off). 2 (yellow) INHIBIT While the switch doesn t produce any pulses its internal state is periodically refreshed with the corresponding circuits. To avoid the undesired interference with PULSE signal, internal refreshing should be suppressed with INHIBIT signal. When switch is operated with <20kHz rep. rate, 5V INHIBIT signal should be applied at least 100ns before PULSE signal. At higher repetition rate INHIBIT signal isn t used. 3,4 (black) INTERFACE RETURN Return of both interface circuits PW JUMPER PW JUMPER selects the switch s operating mode. When PW JUMPER is off (removed), the switch produces high voltage pulses of the only width, namely approx. 14 ns. When PW JUMPER is set on, the switch produces pulses repeating incoming PULSE signal.

6 SPECIFICATIONS parameter HVSW- C HVSW- W pulse amplitude up to 4kV rise time (10-90% level) < 7 ns fall time (10-90% level) < 7 ns pulse width (at 10% level) < 14 ns (fixed, with PW JUMPER on (*) ) ns (adjustable, with PW JUMPER off (*) ) delay time < 100 ns jitter ± 250 ps cooling conductive cooling through the bottom water cooling through the internal channels power rating (max power consumption allowed) 70 W 350 W max. rep. rate 1 MHz or power rating limit (what s less) HV power consumption power consumptions vs output voltage (5pF load, 200kHz rep.rate) 800V 7.5W 1600V 22.0W 2400V 43.0W 3200V 70.0W 4000V 102.5W power consumption vs repetition rate: the dependence is linear rated performance 5pF, 3.2kV, 200kHz 5pF, 3.2kV, 1000kHz inputs high voltage (DC) low voltage (15V DC) Pulse TTL signal (*), Inhibit TTL signal (*) outputs high voltage output (pulsed) protections overheating dimensions 113x90x53 mm weight about 1.0 kg (*) see Interface section for the description HOW TO ORDER? The ordering code has the format as below: HVSW- X, where X the cooling type (C for conductive cooling through the bottom, W for the water cooling) Example: HVSW- C

7 HIGH VOLTAGE POWER SUPPLIES Each high voltage switch requires some high voltage power supply for its feeding. HV OUTPUT INTERFACE MAINS DC high voltage power supply (is shown without upper side of the coverage case) INTERFACES MAINS 1,4 MAINS 1 230V AC line connection 3,6 MAINS 2 2,5 N/C - HV OUTPUT 1,4 (red) HIGH VOLTAGE High voltage output (DC, positive) 3,6 (blue) HV RETURN High voltage output (DC, negative) 2,5 N/C -

8 INTERFACE 15 pin D- SUB female connector. SPECIFICATIONS 1 (red) ENABLE The output is disabled till 5V ENABLE signal is applied to this pin. 7 (yellow) HV PROGRAM Analog voltage (0-10V) applied to this pin defines the output voltage. 10V corresponds to 4kV DC V DC Auxiliary output, may be used for stand alone operations or for other purposes. 8,15 (black) INTERFACE RETURN Return of all the interface circuits. parameter input voltage max. output voltage max. output power auxiliary output interface dimensions weight value 230 VAC, 1 Ø, 50/60 Hz 4 kv 500 W +15V DC, 100 ma current capability (may be used for feeding stand- alone operations) analogue 250x180x70 mm 2.0 kg

9 THE CONTROL BOARD (THE CONTROL UNIT) The second key element requested by pulse picking applications is the control board capable to adjust electrical pulses relatively to optical pulses. In the simplest case the control board solves namely this task, i.e. aligns the sequence of high voltage pulses relatively to the train of optical pulses. In dependence on high voltage switch modification it may be either pulse picker or regenerative amplifier driver. In the most advanced case the control board takes care of complete pico- or femtosecond laser, including one pulse picker and one regenerative amplifier. seed laser up to 75MHz regenerative 1 stretcher PD-2 amplifier 2 up to 100kHz SW-1 SW-2 PD-1 HV-1 control board HV-2 APPEARANCE / DIMENSIONS +15V DC low voltage input to feed the control board (+15V +24V DC acceptable, +15V DC highly recommended) RS- 232 connection to the computer, is used to set up all internal parameters

10 HV 1, HV 2 connection of two high voltage DC sources; turning them on and off, setting the high voltage level ENABLE enabling / disabling of board s outputs DELAY 1 connection of the pulse picker s switch (important!) DELAY 2 connection of the amplifier s switch (important!) PD 1, PD 2, PD 3 three connectors for photodiode assemblies: PD 1 (SYNCHRO) synchronization to the optical train assembly should be of TYPE 1 PD 2 (INTERRUPT) (optional protective feature) the control board releases the optical pulse from the amplifier in the case of the failure (not receiving the signal from this photodiode within 100ns); of course this feature may be turned off; assembly should be of TYPE 2 PD 3 (OUTPUT) may be used as feedback from the very output of the system or in another way; assembly should be of TYPE 2 TIME DIAGRAM AND THE SYNCHRONIZATION The control board contains internal clock that generates permission pulses with khz repetition rate. Once such permission pulse is generated, the control board waits for input synchronization signal from the photodiode assembly PD 1. Immediately afterthen output signals in both pulse picker and amplifier channels are generated, adjusted with programmable delay relatively to the synchronization signal. INTERFACES DELAY 1, DELAY 2 1 (red) PULSE Pulse signal produced with the control board and applied to the high voltage switches 2 (yellow) INHIBIT Inhibit signal (automatically generated with the control board in the case of need) 3,4 (black) RETURN Return of both circuits

11 PD 1, PD 2, PD 3 1 (transp.) PD OUTPUT Signal coming from the photodiode assembly to the control board must be applied to this pin 2 (orange) +15V DC +15V DC voltage needed to feed photodiode assemblies is produced with the control board 3 (green) THRESHOLD Analogue signal used to set up photodiode threshold (0-10V, 10V corresponds to the maximal threshold) is generated with the control board at this pin 4,5,6 RETURN - HV 1, HV 2 1 (red) ENABLE Enables / disables the corresponding high voltage source 2 (yellow) HV PROGRAM Sets up the output voltage of the corresponding HV source 3,4 (black) RETURN - ENABLE 1 (yellow) ENABLE 5V ENABLE signal applied to this pin permits PULSE signals to the high voltage switches. Otherwise PULSE signals are blocked. 2 (blue) RETURN - Alternatively output pulses may be enabled/disabled with ENABLE JUMPER located close to ENABLE connector. +15V DC 1,2 (red) +15V DC +15V...+24V DC input voltage 3,4 (blue) RETURN (+15V DC is strongly recommended)

12 RS (brown) TX - 2 (blue) RX - 3,4 (black) GND - For proper connections to the computer DR and CS should short- circuited (interconnected) at the computer site. RS- 232 INTERFACE COMMANDS DESRIPTION RS- 232 connection parameters: bps, 8 data bits, 1 stop bit, no parity. Command format is: {command} {data} {end- of- line} command is 1-3 character long (see list below) data is ASCII- string date and command are separated with the space symbol end- of- line symbols are \r\n or \n ls1, ls2, ls3 sets threshold of the corresponding photodiode (units, 0 to 255 ) mp1, mp2, mp3 checks the state of the corresponding photodiode ( 1 if photodiode sees the light, 0 if it doesn t) Important note: All the delays introduced with the control board are physically generated by two different circuits. So two different delays (coarse delay and fine delay) should be specified by the customer. The resulting delay is a sum of coarse delay and fine delay. d1 sets coarse delay of the pulse picker s switch (units, 0 to 5, each unit is one period of your seed oscillator) d2 sets coarse delay of the amplifier s switch (rising edge, units, 0 to 5, each unit is one period of your seed oscillator) d3 sets coarse delay of the amplifier s switch (falling edge, units, 10 to 255, each unit is one period of your seed oscillator) dl1 sets fine delay of the pulse picker s switch (units, 0 to 255, by default 255 corresponds to approx. 25ns) dl2, dl3 sets fine delay of the amplifier s switch (of rising and falling edge correspondingly) (units, 0 to 255, by default 255 corresponds to approx. 25ns) lh1, lh2 sets output voltage of the corresponding HV source (units, 0 to 255, by default 255 corresponds to 4kV) e1, e2 enables/disables the corresponding HV source ( 1 enables, 0 disables) f sets output repetition rate (khz, 0.1 to 1000 ) l enables/disables amplifier protection via PD2 (INTERRUPT) ( 1 enables, 0 disables) LS1, LS2, LS3, D1, D2, D3, DL1, DL2, DL3, LH1, LH2, E1, E2, F, L returns the corresponding set point

13 PHOTODIODE S THRESHOLD AND TRIGGERING Since the photodiode processes the very fast optical pulses it s very difficult to measure the optical pulse amplitude using standard techniques. To make it possible our photodiode assemblies have variable threshold of the triggering. Pulses with amplitude below the threshold are invisible. In other words the wider is the range of threshold where the pulse is visible (the photodiode was triggered) the higher is the pulse amplitude. SPECIFICATIONS dimensions weight parameter value 145x105x55 mm 0.2 kg PHOTODIODE ASSEMBLIES PIN 1 PIN 6 INTERFACES INTERFACE SPECIFICATIONS 1 (orange) +15V DC Feeding voltage 3 (green) THRESHOLD Analog voltage applied to this pin sets the threshold of the photodiode s triggering. 5 (transp.) PD OUTPUT Output from the photodiode (5V if photodiode sees the light, 0V if doesn t). Output is pulsed, pulse width is about 100ns. 2,4,6 RETURN photodiode type input output dimensions weight parameter value / description PIN diode +15V DC TTL pulses 60x40x20 mm 0.1 kg MODIFICATIONS / HOW TO ORDER?

14 There are two different modifications of the photodiode assembly. The first modification is very fast and can be used in PD1 position (synchronization to the optical train). The second modification is quite slow and should be used in PD2 and PD3 positions. Photodiode assembly, TYPE 1 ordering code for PD 1 position Photodiode assembly, TYPE 2 ordering code for PD 2 and PD 3 position

15 SOFTWARE The simple Windows XP / Windows 7 software to communicate with the control board is described below.