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 ?