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

8GeV4GeV

1GeV

λ=1064nm

8GeV4GeV

1GeV

λ=532nm

Motivation of upgrade

Gain: 7000 15000

Optical Layout

Faraday Isolator

Vacuum Gauge

Cavity Locking

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

PID-Regulator

Non-tunable Laser Phase Modulator

Beam Splitter Cavity

Photo detector

Oscillator

Phase Shifter

MixerLow Pass Filter

0Error signal

Photo detector

Beam Splitter Cavity

Oscillator

Phase Shifter

MixerLow Pass Filter

0

Tunable Laser

PID-Regulator

Error signal

FSR=170 MHz, Cavity bandwidth=80 kHz

Snapshot of oscilloscope

FSR=170 MHz, Cavity bandwidth≈80 kHz,

The error signal

Fast and Slow ramps

Slow ramp -> Finding the TEM00 mode, creating a single transmission peak

Fast ramp -> At a certain TEM00 mode, creating multiple peaks

Slow ramp

Fast Ramp

Transmission peaks

Previous locking by mirror piezo Feedback signal

Error signal

reflection

transmission

PZT

Previous locking was not stable, poor resolution of the piezo drive caused oscillations.

1064nm 532nm

Innolight GmbH, Germany▪809 nm Pump Diodes▪1064 nm Nd:YAG▪532 nm SHG via PPKTP

0

0.2

0.4

0.6

0.8

1

1.2

300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000

Promethues green laser

Index of Modulation

Modulation frequency

PZT resonace

Choose operation fre 600-1000

Current locking by laser piezoFrequency feedback

Error signal

transmission

reflection

PZT

locking has been achieved by feeding the error signal to the laser piezo.

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.

Microcontroller based locking system

• ARM7 TDMI core, 16-bit/32-bit 44 MHz RISC Processor

• Multichannel, 12-bit ADC, 12 bit DAC

Fast ramp

Slow ramp

PDT signal

Fast ramp

Slow ramp

PDT signalSo far we made good progress in being able to search for strong mode and generating lock trigger.

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