FSS Frequency Stabilisation System

Overview Why we need FSS:  Stabilise the optical frequency of fibre laser to +3 kHz  Use Rb frequency standard at 780 nm access from 1560 nm SHG access from 1560 nm SHG

Tuning control  V Tuning over 10 GHz  +70 µV ≡ +3 kHz  Stabilise to 3 kHz  Stabilise circuit temperature  All voltage variations due to lock-in signals  Peltier Cooler

Peltier Cooler  Heat pump uses Peltier-Seebeck effect  Array of p and n type semiconductors  Transfers heat from one face to the other  depending on current flow

Experiments  Evaluation board which controlled Peltier test set- up  Experiments done by adjusting set-point voltage and looking at how the Peltier temperature changed  Measured the voltage across the module; THERM voltage, and convergence

Results  0.7 V-4 A power supply to get 25 °C  Gradient of linear region agreed with specification  Convergence between THERM and set-point deviated further from 100 µV at higher temperatures

Hall Probe  Magnetic field  Single turn inductive loop in lines of magnetic flux

 5²S1/2 → 5²P3/2  Magnetic field affect the energy of transition  Ambient fields  4-layer cylindrical shield lined with mu- metal

Results

 Opto-isolator:  Top 4 frequency bits set by DIP switch  FPGA controls bits 8-26

Plans  Test tuning part of system  Spectrum analyser