Scatter Shifter

1. Scatter Shifter

2. Motivation/ goals • Gettingridofscatteredlightreflected back intotheinterferometerfromauxilliaryports • Have a versatile devicethatcaneasilybeinsertedintobeamswithoutexchangingopticalcomponentsfortestingwhether back-scatteringcausesobservednoise. • Tobeused in large diameterbeams

3. Scatter source Mirror Interferometer beam  α r= √(1-2)

4. thefield in theinterferometer thefieldofthescattered beam theresultinginterfered beam the power on a photodiode: andtheresulting in thespectrum:

5. Scatter source Mirror  Interferometer beam  α r= √(1-2)

6. Modulating the field with Ωm gives the resulting field nside the interferometer This gives the intensity on the photodiode: or expressed by Bessel Functions: resulting in the spectrum:

7. We can also write this as: If we compare this to the unmodulated case we see it is just shifted by l*Ω and weighed by the Bessel functions of the first kind:

8. Bessel functionsofthefirstkind J0 J1 J2 J3 J4

9. In theLiterature • Man C N et al, 1978, Suppression of Optical Feedback Effects on Saturated Absorption Signals by Phase Modulation of the Reflected Light, J.Phys E : Scientific Instr. 21 19-21 • R. Schilling et al 1981 A method to blot out scattered light effects and its application to a gravitationalwavedetector, J. Phys. E: Scientific Instr. 14 65-70 • P. Beyersdorf 2001 The polarization Sagnac Interferometer for gravitational Wave Detection, PhD thesis http://www.ligo.caltech.edu/docs/P/P010005-00.pdf

10. Optical arrangement

12. Mechanicalmodeofthesubstrate 24 kHz

16. Scatterersimulations • Resultingnoisespectrum • Movement of the scatter source

17. Shiftingthescatteredlighttohigherfrequencies

18. Higher harmonicsfollowthe Bessel functions

19. Deviation from optimal modulationindex

20. Optical arrangement

21. Reducingtheeffectofscatteredlight