1. FSS Frequency Stabilisation System

2. 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

3. Tuning control 0-200 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

4. 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

5. 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

6. 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

8. Hall Probe • Magnetic field • Single turn inductive loop in lines of magnetic flux

9. 5²S1/2 → 5²P3/2 • Magnetic field affect the energy of transition • Ambient fields • 4-layer cylindrical shield lined with mu-metal

10. Results

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

12. Plans • Test tuning part of system • Spectrum analyser