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External Cavity Diode Laser Controller

DLC102, DLC202, DLC252, DLC502

Revision 9.38

Содержание DLC102

Страница 1: ...External Cavity Diode Laser Controller DLC102 DLC202 DLC252 DLC502 Revision 9 38 ...

Страница 2: ...rformance or use of any of its products The foregoing limitation of liability shall be equally applicable to any service provided by MOGLabs Copyright Copyright c MOG Laboratories Pty Ltd MOGLabs 2007 2017 No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying or otherwise without the prior written pe...

Страница 3: ... controllers change that With each DLC unit we provide everything you need to run your ECDL and lock it to an atomic transition In addition to current and temperature con trollers we provide piezo drivers sweep ramp generator modulator for AC locking lock in amplifier feedback servo system laser head electronics protection board even a high speed low noise balanced photodetector We would like to t...

Страница 4: ...ii ...

Страница 5: ...r output can be dangerous Please ensure that you implement the appropriate hazard minimisations for your environment such as laser safety goggles beam blocks and door interlocks MOGLabs takes no responsibility for safe configuration and use of your laser Please Avoid direct exposure to the beam Avoid looking directly into the beam Note the safety labels and heed their warnings When the laser is sw...

Страница 6: ... Please ensure that the unit is configured for the correct voltage for your AC mains supply before connecting The supply must include a good ground connection CAUTION To ensure correct cooling airflow the unit should not be oper ated with cover removed WARNING The internal circuit boards and many of the mounted compo nents are at high voltage with exposed conductors in partic ular the high voltage...

Страница 7: ...t supplied through the RF connector on the laser headboard is not limited Cable continuity If the laser is disconnected the system will switch to standby and disable all laser and piezo power supplies If the laser diode TEC or temperature sensor fail and become open circuit they will be disabled accordingly Short circuit If the laser diode TEC or temperature sensor fail and become short circuit or...

Страница 8: ... a delay of at least 2 seconds before actual laser emission Mains filter Protection against mains transients Key operated The laser cannot be powered unless the key operated STANDBY switch is in the RUN position to enable protection against unauthorised or accidental use The key cannot be removed from the controller when it is in the clockwise RUN position Interlocks Both the main unit and the las...

Страница 9: ...l be zero extending their operating life In the morning switch back on 1 Switch from STANDBY to RUN 2 Switch the laser diode toggle down on You don t need to adjust the current just wait a few minutes for the diode temperature to equilibrate You should switch your MOGLabs DLC into STANDBY mode at nights and weekends and whenever the laser is not being used for more than a few hours Most lasers nee...

Страница 10: ...transition 5 2 Connections and controls 7 2 1 Front panel controls 7 2 2 Front panel display monitor 10 2 3 Rear panel controls and connections 12 2 4 Internal switches and adjustments 15 2 5 Feedback configurations 19 2 6 Digital control 22 2 7 Internal trimpots 23 3 Operation 25 3 1 Initial configuration 25 3 2 Internal scan control 26 3 3 External scan control 28 3 4 DC Locking 28 3 5 AC Lockin...

Страница 11: ...BR DFB diodes 63 D 1 Fine current control 63 D 2 DC current feedback 63 D 3 Slow current feedback 64 D 4 Lock saturation 64 D 5 Special options 64 E Temperature range 65 E 1 Setpoint and limit protection 65 E 2 Setpoint range negative temperatures 66 E 3 Temperature controller additional parameters 66 F Modulation coils 67 F 1 Field requirements 67 F 2 Coil impedance 68 F 3 Impedance matching 69 F...

Страница 12: ...1 I 3 B1047 B1240 headboards 83 I 4 Headboard connection to controller 85 I 5 Dual piezo operation 86 J Control overview 89 K Connectors and cables 93 K 1 LASER 93 K 2 Photodetector 94 K 3 Interlock 94 K 4 Digital control 95 L PCB layout 97 M 115 230 V conversion 99 M 1 Fuse 99 M 2 120 240 V conversion 99 References 103 ...

Страница 13: ...lectric Peltier cooler TEC and temperature sensor via the laser head interface board which is provided For operation with DBR DFB diodes please see appendix D The front panel display and selector switch can be used to monitor the diode current current limit diode dropout voltage temperature temperature setpoint and TEC current see figure 1 1 t n e r r u C d o M p m e T r o r r E t u p n I A m A V ...

Страница 14: ...o 70 sweeps per second see figure 1 2 Critical DLC signals can be monitored using the CHANNEL A and CHANNEL B outputs on the rear panel synchronised to the TRIG trigger output which should be connected to the equivalent inputs on a two channel oscilloscope The particular signals are selected from the front panel CHAN A and CHAN B selector switches The signals are described in detail in the followi...

Страница 15: ...e diode current either manually as the FREQUENCY offset is adjusted when modehops are observed The current can also be automatically biased during the frequency sweep if BIAS is enabled via the internal DIP switch 4 see appendix C Note that adjusting the frequency offset FREQUENCY knob will affect the diode current if BIAS is enabled but it may still be necessary to adjust the diode current as FRE...

Страница 16: ...ffsets λ 4 λ 4 Figure 1 4 Schematic setup for DC locking to an atomic transition PD is the DLC photodetector BS beamsplitter M mirror λ 4 a quarter wave retarder The schematic shows a saturated absorption spectroscopy arrange ment but often simply locking to the side of a Doppler broadened absorption peak will be adequate The photodetector can be used in single channel mode default or with balance...

Страница 17: ...nal modulator In particular it is designed to drive a Zeeman shift modulation coil surrounding the atomic reference vapour cell see appendix F Figures 1 5 3 5 3 6 show examples of AC locking arrangements using a coil to Zeeman modulate the atomic reference or an acousto optic modulator AOM for modulating the frequency of the beam passing through the vapour cell If preferred the modulator oscillato...

Страница 18: ...6 Chapter 1 Introduction ...

Страница 19: ... the high voltage piezo power and the main on board low voltage power In RUN mode the DLC activates all circuits including the laser cur rent driver and piezo drivers The diode current is disabled and the STACK is on but not scanning until the laser enable switch is ON On first power up the STANDBY indicator will be red this is normal and indicates there has been a power failure since last switche...

Страница 20: ...n may be limited by the minimum and maximum voltage that can be applied to the actuator see detailed description in section A 2 PHASE When AC locking the controller demodulates the error signal from the detected light intensity PHASE adjusts the relative phase be tween the internal reference modulator and the detected signal from 0 to 360 When DC locking the sign of the error signal can be flipped...

Страница 21: ...lowing for small adjustment of the lock frequency SCAN LOCK Switch between scanning mode and lock mode When switching from scan to lock the controller will first reset the scanning actuator usually STACK to the offset voltage at the trigger point and then lock to the nearest frequency at which the error signal is zero Sign of fast current feedback The sign of the slow feedback can be changed with ...

Страница 22: ...ge Voltage on thermoelectric Peltier cooler V Frequency Frequency actuator offset usually slow piezo normalised to a range of 1 Note The current display shows the current set point not the actual diode current If BIAS is enabled then during the scan the actual diode current will be higher or lower than that shown depending on the adjusted value of the BIAS trimpot The current limit circuit pre ven...

Страница 23: ... and CHAN B selectors Input Photodetector 30 mV µW Filter Filtered photodetector 40 kHz low pass Freq Frequency scanning actuator STACK 1 V 48 V Slow Slow feedback STACK 1 V 0 24 V DISC 1 V 4 8 V Fast Current feedback 1 V 100 µA CHAN B Input Photodetector 30 mV µW Error Feedback error Current Diode current 2 V full scale Mod Modulator output current 1 V A Temp Temperature error 10 V C Thus 20 10 8...

Страница 24: ...ower after the input mains filter This outlet should be used only to power a monitoring oscilloscope It is provided to minimise ground loop noise problems Fan The fan speed is temperature controlled Interlock The DLC will not power on the laser unless the pins on this connector are shorted A standard 2 1 mm DC plug is provided LASER Connection to laser head This connector provides diode current tw...

Страница 25: ...ion 2 4 for more detail SWEEP PZT MOD Input for externally generated frequency control DIP switch 9 and or DIP switch 13 or for piezo DISC modulation DIP switch 14 This signal is added to the internal error signal if DIP switch 15 is on If DIP switch 9 is on the internal sweep ramp is replaced with the external sweep input In that case the external sweep signal should be 0 to 2 5 V and should cros...

Страница 26: ...er Slower sweeps are recommended usually 10 or 20 Hz works well but if ringing is observed at the start of the sweep reduce fsweep MOD OUT Connection to external modulator output is 0 to 500 mA 8 V Current sensing with 1 Ω sense resistor It can be directly connected to a 50 Ω load giving a voltage of 5 V if Iset is adjusted to 100 mA See appendices F G Imod Modulation depth the range of current mo...

Страница 27: ...local safety regulations 120 V Link LK2 near LK1 and 160 V test point can be shorted to limit the piezo stack voltage to 120 V or removed to increase it to 150 V DIP switches OFF ON 1 DISC fixed DISC ON 2 STACK fixed STACK ON 3 Current dither OFF Current dither ON 4 Current bias OFF Current bias ON 5 Internal error External error 6 External current mod OFF External current mod ON 7 AC lock DC lock...

Страница 28: ...antially extend the mode hop free scan range of the laser see Appendix C DIP 5 External error When ON replaces the internally generated error signal with the externally derived error signal provided to the ERROR back panel input see section 3 6 DIP 6 External current modulation When ON the provided ERROR CURR MOD is added to the fast servo output before the FAST gain is applied The input therefore...

Страница 29: ... applications To reverse the sign of DISC reverse the error signal first and then adjust the sign of the STACK and current feedback Note The feedback to the STACK actuator reverses with DIP 1 and so DIP 10 should also be flipped when DIP 1 is flipped or the PHASE adjusted to reverse the error signal See also section 2 5 DIP 12 DC current feedback Current feedback is normally AC coupled be cause sl...

Страница 30: ...s the internally generated slow piezo feedback error signal The fast current feedback path is unaltered except where overridden by DIP 16 see section 2 5 DIP 12 16 Switches 4 12 16 allow operation of DFB DBR lasers without external cavity feedback and thus with only current as an actuator See section 2 5 and Appendix D for more details ...

Страница 31: ...actual closed loop unity gain frequencies will depend on the particular laser diode and piezos used and on the reference signal so the frequencies are only a guide For CURRENT feedback phase lead adjust can increase the band width to 40 kHz Summary of configurations DIP 16 10 2 1 Description A OFF OFF ON ON STACK slow DISC fast B ON ON ON ON STACK slow DISC fast C OFF ON ON OFF STACK fast DISC fix...

Страница 32: ...w frequency feedback The combined current feedback gain is reduced 25 In this configuration the error signal must be re versed that is the error signal should have a positive slope at the lock point the current feedback polarity toggle switch should be down Note DIP 10 is ON C STACK fast DISC fixed STACK 40 dB decade BW 750 Hz DISC fixed CURRENT 20 dB decade BW 15 kHz High gain fast output to STAC...

Страница 33: ...NT only STACK fixed DISC fixed CURRENT flat BW 15 kHz DIP 12 should be ON for DC CURRENT feedback DIP 4 ON to drive the current with the scanning ramp For DBR and DFB lasers and ECDLs when it is desirable to operate without piezo actuators ...

Страница 34: ...if the front panel switch is up FAST HIGH to FAST lock HOLD HIGH to freeze STACK With HOLD active the feedback to the slow piezo will be fixed by a sample and hold circuit The diode current can then be modulated via the rear panel CURR MOD input with DIP switch 6 ON to jump the laser frequency quickly without the error feedback circuit competing with the external modulation External current modula...

Страница 35: ...an be modulated directly The modulation depth is then controlled by the rear panel Imod trimpot The limit to the current modulation is factory set via RT6 RT12 A phase lead circuit is included on the current feedback channel to boost the output at higher frequencies tens of kHz RT12 con trols the phase lead and can be adjusted for different diodes see appendix 4 RT13 Offset adjustment for active t...

Страница 36: ...24 Chapter 2 Connections and controls ...

Страница 37: ... initiate temperature control The indicator should change from red or orange to green If the indicator is not green ensure that the TEC and temperature sensor are correctly wired 3 If the controller is switched back to STANDBY all electronics will be powered down except for the temperature controller which will continue to operate normally 4 Adjust the temperature setpoint first select Temp set on...

Страница 38: ...revent current flowing to the diode such as detecting main cable disconnect open circuit on the rear panel or activation of laser head interlocks 3 2 Internal scan control In normal SCAN mode a sawtooth ramp is supplied to the piezo Figure 3 1 causing the laser frequency shift Typically a pho todiode signal is measured as the frequency is swept to identify resonant features or isolate transitions ...

Страница 39: ...works well but if ringing is observed at the start of the sweep reduce fsweep Figure 3 2 is an example of an absorption spectrum acquired with the simple scanning configuration with BIAS current feed forward The transmission of the laser through a rubidium vapour cell was de tected on the DLC photodetector as the laser frequency was scanned through the 52S1 2 52P3 2 transitions Rb87 F 2 Rb85 F 3 R...

Страница 40: ...AN LOCK is set to SCAN the external signal will be used The front panel knobs FREQUENCY and SPAN will then apply offset and attenuation to the external ramp It is recom mended to set FREQUENCY to its midpoint 0 V on the front panel display with Frequency selected and set SPAN to fully clockwise The internal servo can then be used to lock the laser frequency by switching SCAN LOCK to LOCK provided ...

Страница 41: ... the sensitivity to changes in laser power and allows subtraction of the Doppler background from a saturated absorption spectrum When DC locking it is also important to prevent the photodetectors from measuring fluctuations in ambient light e g fluorescent room lights MOGLabs photodetectors are lensed and filtered to minimise the influence of background light but best results will be obtained when...

Страница 42: ...et SLOW and FAST gains to minimum fully anti clockwise 9 Switch SCAN LOCK to LOCK When the laser is locked the pho todetector INPUT signal should be fixed at the value corre sponding to the lock frequency 10 Switch OFF LOCK to LOCK It may be necessary to invert the sign of the fast lock with the switch 11 Increase SLOW and FAST gains to minimise the error signal ideally using an external audio spe...

Страница 43: ...ns for AC locking using saturated ab sorption spectroscopy are shown in Figure 3 5 and 3 6 These are similar to the scheme for DC locking with the addition of a Zeeman coil around the vapour cell which is driven by the DLC Figure 3 7 shows sample traces of the photodetector and error sig nals in AC locking mode for wide and narrow spans These traces were obtained with an 8 cm long Rb vapour cell a...

Страница 44: ...st the GAIN such that the error peaks are roughly 250 500 mV peak to peak Note that larger signals do not improve lock performance 8 Adjust front panel ERROR OFFSET such that the error signal is crossing zero at the desired frequency 9 Set SLOW and FAST gains to minimum fully anti clockwise BS PD 250kHz M M BS Lock in ECDL BS Servo Vapour cell coil AOM λ 4 λ 4 f 150mm f 25mm Figure 3 5 Schematic s...

Страница 45: ...ked the pho todetector INPUT signal should be fixed at the value corre sponding to the lock frequency If the photodetector voltage jumps after engaging the lock the servo needs to be relocked 11 Switch OFF LOCK to LOCK It may be necessary to invert the sign of the fast lock with the switch 12 Increase SLOW and FAST gains to minimise the amplitude of the C1 C2 Ch1 100m V Ch2 100m V 20 0m s C1 C2 Ch...

Страница 46: ... J for block diagrams of the control circuitry for connecting external servos It is important to clarify the distinction between error and control signals an error signal is a dispersive signal with a potential that depends on laser frequency whereas a control signal is a feed back servo signal generated from an error signal usually via a PID proportional integral differential controller When usin...

Страница 47: ...nd should be zero while scanning the DLC 1 Locate R113 near the DIP switches see figure 3 8 2 Install a 0603 package SMD resistor with nominal value 5k 3 Connect the required external control signal to the rear panel SWEEP input 4 Ensure DIP switch 9 is OFF 3 6 3 External piezo lock with external ramp Some servo controllers include their own ramp generators which in some circumstances may be prefe...

Страница 48: ...l ramp 3 6 4 External current lock An external servo can also be used to control the current of the laser In most applications that require fast feedback in this way improved performance can usually be achieved by modulating the laser current directly on the laser headboard Appendix I instead of via the DLC However where this option is unavailable or the range of modulation is limited by the headb...

Страница 49: ...ed by the DLC The locks must be engaged via the external servos providing the signals 3 6 5 External current lock and internal piezo lock In some applications it may be desirable to use a fast external servo to control the laser current and use the MOGLabs DLC to control the piezo In this scenario 1 Connect fast control signal to ERROR 2 Enable fast current control with DIP switch 6 3 Connect slow...

Страница 50: ...38 Chapter 3 Operation ...

Страница 51: ...ature and reduce the effective linewidth as close as possible to the S T limit Achieving the best frequency locking stability requires careful op timisation of the signal to noise ratio SNR of the frequency dis crimination signal obtained from the saturated absorption or other reference Then the phase and gain settings must be optimised preferably by measuring the feedback error signal spectrum 4 ...

Страница 52: ...isation The frequency discriminator ERROR signal is sensitive to the pump and probe polarisations Good polarisers and careful alignment can be very helpful Coil design See appendix F Shielding The Zeeman coil produces substantial magnetic fields oscillating at 250 kHz These fields can readily induce prob lematic potentials and currents in the laser head and or main circuit board In particular it i...

Страница 53: ... If possible an audio frequency spectrum analyser can be used to provide better guidance A generic computer sound card with spectrum analysis software gives reasonable results up to 20 kHz A good sound card 24 bit 200 kHz e g Lynx L22 or E Mu 1212m provides noise analysis up to 100 kHz with 140 dB dynamic range surpassing most standalone audio spectrum analysers at very low cost Connect the spectr...

Страница 54: ...on the diode optical feedback the frequency discriminator noise floor and other details Typically we find that the laser diode itself has a 90 phase lag at 15 to 100 kHz Some compensation for that phase lag is provided by a phase lead compensator see RT12 page 23 Ideally the SLOW and FAST gains should be adjusted to minimise the integrated noise the area under the error spectrum The data in fig 4 ...

Страница 55: ...tivity 100 µA V 1 5 MHz bandwidth RF modulation SMA 50 Ω 160 kHz 2 5 GHz see below BIAS 25 mA over full sweep Temperature controller TEC current max 2 5 A TEC voltage max 9 V TEC power max 22 W Stability 5 mK C Sensor NTC 10 kΩ AD590 AD592 Range 0 30 standard extended range optional Display resolution 0 01 Note The TEC is controlled with a linear regulator which will overheat if the current load i...

Страница 56: ...er LK2 see page 15 Note The maximum piezo drive current is 10 mA which limits the scan rates for piezos with high capacitance For exmaple for a 250 nF piezo the rate should not be greater than 25 Hz Photodetector Photodiodes Si PIN IR filtered 740 nm 1100 nm 1 1 mm2 sensor 10 field of view See appendix H for spectral response Options unfiltered 400 nm 1100 nm 20 70 Coupling AC and DC single or dif...

Страница 57: ...TER 20 dB FAST MASTER 20 dB Bandwidth gains at midpoint SLOW 0 dB at 700 Hz FAST 0 dB at 80 kHz Protection and status External interlock 2 1 mm DC power plug provided Laser head enclosure interlock 2 pin MOLEX connector provided Key switch interlock STANDBY RUN Delayed soft start 3 s delay 3 s ramp Open circuit detect Laser cable TEC temperature sensor Diode current limit Rear panel trimpot Imax ...

Страница 58: ...K switch ON in terlock open head cable dis connected temperature con troller fault detected ORANGE Ready GREEN Diode running Mechanical power Display 4 5 digit LED standard colour red Fan 12 V DC ball bearing Temperature controlled IEC input 110 to 130 V 60Hz or 220 to 260 V 50Hz Fuse 5x20mm anti surge slo blo ceramic 250V 2 5A IEC output Common ground with power input Intended for oscilloscope 1 ...

Страница 59: ...ignal is output via the rear panel TRIG connection for synchronising to an oscilloscope or external experiment The span may be limited by the minimum and maximum voltage that can be applied to the actuator 0 and 120 V 150 V optional That is the ramp may saturate as shown in fig A 2 The period remains fixed and the trigger remains at the centre of the period but the laser frequency will not scan fo...

Страница 60: ...ions 0V 0V 120V time TRIG STACK 5V FREQUENCY SPAN Figure A 2 STACK output voltage and trigger pulse when FREQUENCY is set near the midpoint upper or moved closer to 0 V lower where the output voltage exceeds the maximum range ...

Страница 61: ... faults AC mains off Interlock s disconnected TEC open or short circuit TEC polarity reversed Cable disconnected Temperature sensor disconnected Active temperature sensor connected to thermistor pins Thermistor connected to active sensor pins Temperature out of range 5 C or 35 C External sweep selected DIP switch 9 but no external sweep supplied Wrong AC mains voltage RED AC mains power failure te...

Страница 62: ...ed TEC disabled temperature out of range Any one of 5 12 aux 12 V internal supplies below nominal by more than 1 V External sweep selected DIP switch 9 but no external sweep supplied ORANGE Standby above conditions satisfied diode ready to start GREEN Diode fully operational piezos active If the indicator remains ORANGE after switching the diode ON check the possible faults listed above in particu...

Страница 63: ...R87 R91 L4 H1 C4 C16 R21 C24 C1 K1 C2 U4 L5 R23 L7 R19 R20 C18 R68 R37 R59 RT3 U9 R36 U10 C19 R35 C35 RT4 C30 C28 R67 C34 R71 R58 R77 R76 R92 R69 R88 U25 C214 R72 RT5 R81 R80 U26 R85 D4 R90 RT2 RT1 P3 Y X TO220_KIT P7 Imod P35 Amp Dist Freq Amp D Amp I Figure B 1 250 kHz oscillator trimpots and testpoints 1 Measure test point P35 with a multimeter and adjust RT5 labelled Amp for 1 15 volts P35 is ...

Страница 64: ... right of U59 and adjust RT6 Amp I to obtain a 1 0 V peak peak sine wave For older controllers serial numbers with a 7 or smaller number in the 6th digit e g A12027 P36 does not exist instead measure pin 15 of U59 5 Finally adjust Imod to the required modulation depth typically about half way 6 turns anti clockwise B 3 1 Disable 250 kHz oscillator If the 250 kHz oscillator is not required it can b...

Страница 65: ... one of the slow actuators STACK DISC STACK feedback has wrong polarity See DIP switch 10 Lock signal zero crossing too far from trigger point Gain too high Try smaller and smaller gain but be careful to ensure that the lock error signal is crossing zero Loop response too fast for actuator The controller is normally shipped with slow channel response gain of 1 0dB around 700 Hz Please contact the ...

Страница 66: ...t very slightly Lock signal zero crossing too far from trigger point Gain too high Try smaller and smaller gain but be careful to ensure that the lock error signal is crossing zero B 4 4 FAST locks only briefly The FAST channel is normally AC coupled see DIP switch 12 with a time constant of 0 1 s Thus with FAST feedback only the laser will drift off resonance Normally the SLOW channel is used to ...

Страница 67: ...1 5 to 2 0 V When the signal crosses through 1 25 V a signal is generated which triggers the control circuits for example to read the state of the front panel toggle switches You can see if that control signal is generated by observing the TRIG output which should transition from low to high periodically If the TRIG output isn t changing then the toggle switch settings are not being updated ...

Страница 68: ...56 Appendix B Troubleshooting ...

Страница 69: ... very similar at adjacent external cavity modes A small change in the internal cavity mode or the grating or filter angle can lead to the overall gain being greater at a mode adjacent to the mode in which the laser is oscillating and the laser then hops to that higher gain mode See Ref 3 for a detailed discussion C 1 Scanning The external cavity length is usually controlled by piezo actuators movi...

Страница 70: ...s the piezo voltage is changed Feed forward current bias adjustment is a feature of MOGLabs DLC controllers Adjustment is straightforward With the laser frequency scanning the current bias control is adjusted until the maximum mode hop free scan range is observed Small changes to the injection current optimise the scan range near the nominal centre frequency Detailed instructions follow A Fizeau w...

Страница 71: ...grating frequency will cause the laser to jump to another external cavity mode where the net gain is higher CHAN B output set to Current 4 Adjust the laser diode CURRENT so that the laser wavelength and power are correct Use the values provided in the original factory test report as a guide 5 If the wavelength is close but not quite correct small adjust ments of either CURRENT or FREQUENCY may be ...

Страница 72: ...some point observe a mode hop For spectroscopy scans it is easier to observe mode hops using the AC error signal from the MOGLabs DLC if current modulation is enabled The mode hop should be at one edge of the scan if so adjust the FREQUENCY so that the scan no longer clips this mode hop i e the scan is free of mode hops and continue adjusting in the same direction until a mode hop is observed on t...

Страница 73: ...rimpot direction If both mode hops are removed repeat the steps above increas ing SPAN until no further improvements can be made to the MHFR 13 If the MHFR is substantially less than expected refer to the factory test report it may be advisable to change mode by in creasing or decreasing the CURRENT to find a nearby single mode current or to rotate the filter or grating slightly to alter the net g...

Страница 74: ...62 Appendix C Mode hops and BIAS ...

Страница 75: ...zo control of frequency very find control of the current is required The coarse CURRENT knob can be used to set the current to within a milliamp or two and the FREQUENCY knob must then be used The FREQUENCY knob is normally used to adjust the piezo actuator offset but it also couples to the current via the current feed forward bias The BIAS trimpot can be adjusted such that the FREQUENCY knob vari...

Страница 76: ...k signals only have small range and with DBR DFB diodes this is easily saturated Use feedback con figuration B see section 2 5 to maximise the lock range Dip switch 1 should be ON D 5 Special options Modifications can be made to the controller including 1 External control of temperature set point for example to en able slow frequency scans via the diode temperature 2 Very slow locking feedback to ...

Страница 77: ... which is close to the current set pot The resis tors can be located in the PCB layout appendix L using your pdf viewer e g Acrobat search function E 1 Setpoint and limit protection R44 Normally 10 k change to 2 k to increase temperature setpoint max imum to 50 C The max setpoint temperature is given by Tsetmax 600k 10k R44 R303 Normally 1 k4 change to 2k0 to increase temperature out of range limi...

Страница 78: ...o a known temperature and adjust RT13 until temperature reads cor rectly RT15 Sets the maximum TEC current Standard units can drive up to approximately 1 8 A if RT15 is set to the maximum fully CW R323 PID proportional gain resistor nominally 499 k in series with Tem perature Gain trimpot on rear panel 1 M reduce R323 to 10 k for lasers with large thermal capacity e g Toptica DL 100 R332 PID diffe...

Страница 79: ...ow cost using a solenoid coil wrapped around an atomic vapour cell as shown below Figure F 1 Vapour cell Zeeman coil and primary excitation coil mounted on PCB available from MOGLabs F 1 Field requirements Ideally the Zeeman dither coil should produce a frequency shift of about half the peak width typically a few MHz Atomic stretched state transitions will be Zeeman shifted by µB eh 2me 1 4 MHz Ga...

Страница 80: ...and l is the coil length In practice the inductance will be less e g see Wheeler 6 LWheeler N2r2 228r 254l mH F 2 4 where N is the total number of turns r is the coil radius in metres and l is the length in metres l 0 8r We have found that for dimensions typical of coils wound around vapour cells these two formulae agree within a factor of two Note that the inductance increases with n2 whereas the...

Страница 81: ...lew rate of 6 V µs This can be impedance matched to a high current coil using a trans former or quite effectively by directly winding a primary on the main Zeeman coil as shown in the photo above For the main Zeeman coil 0 4 mm to 0 6 mm diameter wire wound around the vapour cell about 120 to 200 turns works well The coil is balanced for the standard modulation frequency of ω 250 kHz using a capac...

Страница 82: ...dequate voltage rating F 4 Tuning To maximise the current in the secondary the capacitor should be chosen to tune the circuit to the DLC modulation frequency A spec trum analyser with tracking generator is particularly helpful con nect the coil to the TG output and to the SA input and sweep through the resonance see figure Alternately drive the coil with a function generator and measure the magnet...

Страница 83: ...kHz F 5 Shielding Large magnetic fields oscillating at 250 kHz can readily cause prob lematic electromagnetic interference EMI Induction in the laser head or the cable to the laser head can easily produce substantial diode current modulation The coil and vapour cell should be lo cated far from the laser and from the controller or shielded with soft iron or a high permeability alloy such as mu meta...

Страница 84: ...72 Appendix F Modulation coils ...

Страница 85: ...iode injection current DIP switch 3 or drive an external modulator such as an electro optic modulator EOM or acousto optic modulator AOM G 1 Coupling circuit The DLC provides a current controlled modulation output with 1 Ω sense resistor It can be directly connected to a 50 Ω load producing a voltage of 5 V with Iset adjusted to 100 mA Impedance matching and a DC level shift may be needed to drive...

Страница 86: ...tion e g 10 MHz via the SMA RF input on the laser head board Very narrow linewidths can be achieved with suitably high bandwidth frequency discrimination for example by phase locking two lasers The diagram below shows an arrangement to lock two lasers to an EIT electromagnetically induced transparency reso nance which obtained a beatnote linewidth below 1 kHz 7 Photodiode Phase shifter Lowpass 2 5...

Страница 87: ... is returned to the external error input on the probe laser MOGLabs DLC which locked the laser with bandwidth up to about 40 kHz The error signal was also coupled through a single stage passive phase lead high pass filter and then combined with the 10 MHz modulation using a passive bias tee and injected into the SMA modulation input to provide feedback bandwidth of about 600 kHz Att 25 dB RBW 300 ...

Страница 88: ...76 Appendix G External modulators and injection current modulation ...

Страница 89: ... rear socket and cable provided A number of M4 and 8 32 threaded holes allow mounting in differ ent configurations to minimise the footprint on an optical bench see figure H 2 Figure H 1 MOGLabs DLC balanced differential photodetector 5 7 2 60 30 1 2 Figure H 2 M4 mounting holes are marked with a dimple others are 8 32 Single channel photodiode 1 differential signal 1 2 77 ...

Страница 90: ...nce angles are also available Photodiode Specifications Parameter Standard Options Spectral range 10 of max 750 1100 nm 400 1100 nm Peak sensitivity 900 nm 850 nm Half angle 10 10 20 75 Sensitive area 1 1 mm2 Max incident power 500 µW Apparent sensitivity CHAN A 30 mV µW λ nm 0 Relative detection efficiency 400 600 800 1000 1200 20 40 60 80 100 0 400 600 800 1000 1200 20 40 60 80 100 λ nm Relative...

Страница 91: ...d headboard using Hirose DF59 swing lock wire to board connectors Digikey H11958 ND and H11957CT ND plug and crimp pin The B1047 headboard pro vides high bandwidth active current modulation for wide bandwidth frequency stabilisation and linewidth narrowing for example using a high finesse optical cavity or polarisation spectroscopy Higher bandwidth is provided by the B1240 headboard which further ...

Страница 92: ...mall circuit board to connect directly to the diode is also available from MOGLabs with SMA and MOLEX connectors The MOGLabs DLC does not provide a mechanism for optical power control or measurement for diodes with an internal photodiode Figure I 1 MOGLabs DLC laser head board showing headers for con nection of laser diode piezo actuators temperature sensor TEC and head enclosure interlock Connect...

Страница 93: ...elow Disc Figure I 2 MOGLabs B1045 and B1046 laser head boards showing con nectors for laser diode piezo actuator temperature sensors TEC and head enclosure interlock Connectors are Hirose DF59 I 2 1 RF coupling For the B1045 1046 headboard the SMA connector allows high frequency current modulation via a bias tee The RF input is AC coupled with low and high frequency limits of about 30 kHz and 2 5...

Страница 94: ...rect connection to the laser diode Excessive power can destroy the diode which is separated from the head board relay by an inductor Thus the relay does not provide protection from high frequency signals RBW 30 kHz VBW 10 MHz SWT 17 s Att 50 dB TG 30 dBm Ref 20 dBm Center 1 5 GHz Span 3 GHz 300 MHz 70 65 60 55 50 45 40 35 30 25 20 Figure I 3 RF response SMA input on laser headboard to diode SMA ou...

Страница 95: ...s about 10 slower but reduces problems with ground loop noise The B1240 is not suitable for diodes with high compliance voltage typically diodes with wavelength below 600 nm Note that connection to the SMA input will reduce the diode current even if the input voltage is at zero C 5 C 4 R 4 R 7 C 6 R 5 R 6 C 11 R 12 D1 R 10 C 8 R 14 U 3 R 1 C 3 Q 1 R 2 C 1 C 2 R 3 R 11 P2 U1 P5 U2 R 13 C 7 R 9 SMA ...

Страница 96: ...e the diode current by about 1 6 mA B1047 to 2 5 mA B1240 with zero input voltage B1047 B1240 Input range 2 0 V max 2 0 V max Input coupling AC DC DC direct AC DC buffered AC time constant 6 µs 25 kHz 15 µs 10 kHz Phase delay 40 ns 20 ns direct 30 ns buffered Gain bandwidth 3 dB 3 MHz 20 MHz Input impedance 5 k 1 k Current gain 1 mA V 1 mA V Laser diode voltage 10 V max 2 5 V max ...

Страница 97: ... 5V in 24 NTC 1 8 17 24 1 8 17 24 LASER Socket DVI D DL Dual Link Plug DVI D SL Single Link Do not use SL cables Missing pins Figure I 5 Headboard connector Note that the pinout is different to that of the matching connector on the rear of the DLC controller A 10 k thermistor should be connected to NTC and NTC but an AD590 or AD592 temperature sensor can be instead be connected to Tsense Pin 16 sh...

Страница 98: ...tk 2 or Piezo 2 Since DLC revision 9 01 this second feedback channel is dis connected and instead both piezo outputs are driven in paral lel with a variable relative gain adjusted by RT7 near the DIP switches If there is a failure of the STACK electronic driver it is possible to use the DISC driver simply connect the STACK to HD7 Stk 2 Alternate single channel For older controllers to change to th...

Страница 99: ... a P 1 2 r i a P 2 d l e i h S 4 2 P 3 4 r i a P 4 4 r i a P 5 1 e l g n i S 6 2 e l g n i S 7 3 e l g n i S 8 1 r i a P 9 1 r i a P 0 1 d l e i h S 3 1 P 1 1 3 r i a P 2 1 3 r i a P 3 1 5 e l g n i S 4 1 6 e l g n i S 5 1 4 e l g n i S 6 1 0 r i a P 7 1 0 r i a P 8 1 d l e i h S 5 0 P 9 1 5 r i a P 0 2 5 r i a P 1 2 d l e i h S 6 P 2 2 6 r i a P 3 2 6 r i a P 4 2 e l o H t n u o M 1 D 1 R 10k 4 R...

Страница 100: ...88 Appendix I Laser head board ...

Страница 101: ...r enable Dip 3 DC lock enable Dip 7 Differential PD Dip 8 Test H W Dither on off Front panel MOD INPUT Photodiode offset Front panel PHASE 0 360 Front panel Diode current dither Gain ERROR OFFSET Summer Error offset ERROR CURR MOD Rear panel External error enable Dip 5 Front Panel Error signal 250kHz Phase midpoint polarity control Front panel GAIN Figure J 1 Overview of error and control signals ...

Страница 102: ... polarity Stack offset Rear panel Rear panel BNC Disc offset External sweep signal Slow current signal Dip 9 Dip 10 Dip 1 Dip 2 Dip 13 Dip 14 Dip 11 control External sweep signal Dip 15 External piezo control External sweep signal Piezo fast control enable Dip 1 Piezo slow control enable Dip 2 NOT Dip 1 Front panel Span Sweep amplitude Front Panel Scan Lock Front panel or DI 2 Stack piezo signal T...

Страница 103: ... External Dip 16 Piezo current enable Bias gain Front panel Front panel Current gain Front Panel Phase gain RT12 Current polarity Front panel Current control enable FAST Front panel or DI 3 Front Panel or DI 1 soft start Slow current signal Buffer Phase midpoint External Signal Error Current polarity control Rear panel BNC Diode current dither DVI D DL cable Laser Error signal 100uA V 2 5mA V Figu...

Страница 104: ...92 Appendix J Control overview ...

Страница 105: ... below Only high quality digital dual link DVI D DL cables should be used Pin Signal Pin Signal Pin Signal 1 TEC 9 DIODE 17 DISC 2 TEC 10 DIODE 18 DISC 3 Shield 11 Shield 19 Shield 4 TEC 12 DIODE 20 STACK 5 TEC 13 DIODE 21 STACK 6 Tsense 14 Relay GND 22 7 Tsense 15 5V out 23 NTC 8 16 Interlock in 24 NTC 1 8 17 24 1 8 17 24 LASER Socket DVI D DL Dual Link Plug DVI D SL Single Link Do not use SL cab...

Страница 106: ...ap pins 3 4 with pins 5 6 so the pinout on the photodetector connector is different to that on the controller Pin Controller Detector 1 Ground 2 Differential if GND 3 12 V Signal 4 12 V Signal 5 Signal 12 V 6 Signal 12 V 1 3 5 2 4 6 Figure K 2 Photodetector connector on rear panel of DLC and corre sponding connector on photodetector Differential output is enabled if pin 2 is grounded 0 V Single en...

Страница 107: ...or locking and for sample and hold of the lock point as described in section 2 6 The signals are standard TTL compatible 2 4 V HIGH and 0 8 V LOW The inputs are ORed with the front toggle switches such that the signal is activated if either the digital input is active i e HIGH or the toggle switch is on down Pin Signal Pin 1 Laser ON OFF 2 GND 3 Lock Sweep 4 GND 5 Fast Lock 6 GND 7 Hold 8 GND 9 5 ...

Страница 108: ...96 Appendix K Connectors and cables ...

Страница 109: ... C124 R285 C431 R281 R286 R299 R309 L17 R289 R290 R300 R282 C129 R287 R304 N1 R291 R301 R302 C128 R303 R305 RT14 R315 R308 C109 RS2 R577 U69 R572 R576 R571 R589 R259 U70 R579 R261 R270 R511 R260 R604 R607 RS3 R575 N23 N22 R283 R331 L16 P17 R273 U74 R275 U75 RS4 R292 R274 RT13 R306 U82 R332 C132 U83 R323 C137 R324 R344 R333 R311 U84 R318 R316 C138 R325 R326 R317 R319 C144 U88 C143 U86 R49 RT15 U94 ...

Страница 110: ...98 Appendix L PCB layout ...

Страница 111: ...in switch on the rear of the unit Fig M 1 Figure M 1 Fuse catridge showing fuse placement for operation at 230 Vac M 2 120 240 V conversion The controller can be powered from AC 50 to 60 Hz 110 to 120 V 100 V in Japan or 220 to 240 V To convert between 115 V and 230 V the fuse cartridge should be removed and re inserted such that the correct voltage shows through the cover window 99 ...

Страница 112: ...ert a screwdriver into the recess at the top of the cartridge do not try to extract using a screwdriver at the sides of the fuseholder see figures Figure M 3 To extract the fuse cartridge insert a screwdriver into a recess at the top of the cartridge When changing the voltage the fuse and a bridging clip must be swapped from one side to the other so that the bridging clip is always on the left and...

Страница 113: ...conversion 101 Figure M 4 Bridge left and fuse right for 230 V Swap the bridge and fuse when changing voltage so that the fuse remains on the right hand side see below Figure M 5 Bridge left and fuse right for 115 V ...

Страница 114: ...102 Appendix M 115 230 V conversion ...

Страница 115: ...below 100 khz with external cavity diode lasers Appl Opt 48 36 6961 2009 i 5 W Demtro der Laser Spectroscopy Basic Concepts and Instru mentation Springer Berlin 2e edition 1996 4 39 6 H A Wheeler Simple inductance formulas for radio coils Proc I R E 16 1398 1928 68 7 S C Bell D M Heywood J D White and R E Scholten Laser frequency offset locking using electromagnetically induced transparency Appl P...

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Страница 118: ...aboratories Pty Ltd 49 University St Carlton VIC 3053 Australia Tel 61 3 9939 0677 info moglabs com c 2007 2018 Product specifications and descriptions in this doc ument are subject to change without notice ...

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