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Scatter Shifter

Scatter Shifter. Motivation/ goals. Getting rid of scattered light reflected back into the interferometer from auxilliary ports Have a versatile device that can easily be inserted into beams without exchanging optical components for testing whether back- scattering causes observed noise .

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Scatter Shifter

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  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

  11. Mechanicalmodeofthesubstrate 24 kHz

  12. Scatterersimulations • Resultingnoisespectrum • Movement of the scatter source

  13. Shiftingthescatteredlighttohigherfrequencies

  14. Higher harmonicsfollowthe Bessel functions

  15. Deviation from optimal modulationindex

  16. Optical arrangement

  17. Reducingtheeffectofscatteredlight

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