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Green cavity progress Botao Jia botaoj@jlab May 17 2007 Advisors:

Green cavity progress Botao Jia botaoj@jlab.org May 17 2007 Advisors: Dr. Nanda Sirish, Dr. Wu Ying HAPPEX   Collab.   Mtg.   May 17-18, 2007. Motivation of upgrade. λ =1064nm. λ =532nm. 8GeV. 8GeV. 4GeV. 4GeV. 1GeV. 1GeV. Gain: 7000 15000. Optical Layout. Vacuum Gauge.

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Green cavity progress Botao Jia botaoj@jlab May 17 2007 Advisors:

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  1. Green cavity progress Botao Jia botaoj@jlab.org May 17 2007 Advisors: Dr. Nanda Sirish, Dr. Wu Ying HAPPEX   Collab.   Mtg.   May 17-18, 2007

  2. Motivation of upgrade λ=1064nm λ=532nm 8GeV 8GeV 4GeV 4GeV 1GeV 1GeV Gain: 700015000

  3. Optical Layout Vacuum Gauge Faraday Isolator

  4. Cavity Locking Beam Splitter Beam Splitter Phase Modulator Non-tunable Laser Tunable Laser Cavity Cavity Oscillator Oscillator PID-Regulator PID-Regulator Photo detector Photo detector Phase Shifter Phase Shifter 0 Error signal 0 Error signal Mixer Mixer Low Pass Filter Low Pass Filter Use Pound-Drever-Hall method to extract the phase of the resonace by using frequency modulation of the main laser beam. The phase of the resonace is used as the error signal in the feedback loop. 1. Using Mirror Piezo 2. Using Laser Piezo

  5. The error signal Snapshot of oscilloscope FSR=170 MHz, Cavity bandwidth≈80 kHz, FSR=170 MHz, Cavity bandwidth=80 kHz

  6. Fast and Slow ramps Slow ramp Fast Ramp Transmission peaks Slow ramp -> Finding the TEM00 mode, creating a single transmission peak Fast ramp -> At a certain TEM00 mode, creating multiple peaks

  7. Previous locking by mirror piezo Error signal reflection transmission Feedback signal PZT Previous locking was not stable, poor resolution of the piezo drive caused oscillations.

  8. Promethues green laser Innolight GmbH, Germany ▪809 nm Pump Diodes ▪1064 nm Nd:YAG ▪532 nm SHG via PPKTP Index of Modulation PZT resonace Modulation frequency Choose operation fre 600-1000 1064nm532nm

  9. Current locking by laser piezo Frequency feedback PZT locking has been achieved by feeding the error signal to the laser piezo. reflection Error signal transmission

  10. Locking monitored via Epics Reflection Temperature Scan Transmission 6 mins min Locking for several mins duration has been achieved. 1. Regualtor is able to recover quickly within milliseconds. 2. Fluctuations are huge. Have to improve signal to noise ratio. 3. Goes out of lock. We are working on extending lock from mins to hour level.

  11. Microcontroller based locking system • ARM7 TDMI core, 16-bit/32-bit 44 MHz RISC Processor • Multichannel, 12-bit ADC, 12 bit DAC Fast ramp Fast ramp Slow ramp PDT signal Slow ramp PDT signal So far we made good progress in being able to search for strong mode and generating lock trigger.

  12. Conclusions: Minutes level locking has been achieved. The longest record so far is 6 minutes. Investigating stability issues to achieve hours level locking. Thank You

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