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FSS

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. Tuning control. 0-200 V Tuning over 10 GHz + 70 µV ≡ + 3 kHz Stabilise to 3 kHz

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FSS

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  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

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

  8. 5²S1/2 → 5²P3/2 • Magnetic field affect the energy of transition • Ambient fields • 4-layer cylindrical shield lined with mu-metal

  9. Results

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

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

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