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Homodyne detection: understanding the laser noise amplitude transfer function

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Homodyne detection: understanding the laser noise amplitude transfer function

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  1. Homodyne detection:understanding the laser noise amplitude transfer function Jérôme Degallaix Ilias meeting – June 2007

  2. Going DC Stefan’s talk this morning Laser PRM SRM Carrier local oscillator

  3. Measure the laser intensity noise transfer function • Switch off laser power stabilisation loop • Inject white noise into the laser pump • Record dark port spectrum

  4. Input ? Reflected PRC Laser After laser After MC Reflected BS output

  5. The measured TF

  6. Optical fields FSR = 125 kHz Laser

  7. Optical fields FSR = 125 kHz fMI = 14.9 MHz Laser

  8. Optical fields FSR = 125 kHz fMI = 14.9 MHz fSR = 9.01 MHz Laser

  9. Carrier TF Simple Michelson • Flat response due: • Arm asymetries • Dark fringe offset

  10. Carrier TF With SRM Peak due to SRM

  11. Carrier TF Including the higher order optical modes • Increase the amplitude of the TF • Flat the response at high frequency

  12. TF with SR sidebands Resonance peak of the sidebands!

  13. TF with SR sidebands

  14. TF with SR sidebands Including the higher order optical modes Shape of the sidebands resonance different!

  15. TF with MI sidebands

  16. TF with MI sidebands Including the higher order optical modes

  17. Changing the PRC FSR A little test to confirm what we understand...

  18. Changing the SRC FSR Another test...

  19. Does it match the experiment ? • Adjust the overall gain of the simulated TF • Thanks to Andreas for the tuning of the parameters

  20. To sum up... Due to the signal recycling mirror Due to SR sidebands and higher order optical modes • Overal magnitude depends of: • arm detuning • magnitude of higher order optical modes Due to second order optical modes Due to MI sidebands

  21. So ?