1. Scatter Shifter

2. 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.  To be used in large diameter beams

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

4. and the resulting in the spectrum : the field in the interferometer the field of the scattered beam the resulting interfered beam the power on a photodiode:

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

6. Modulating the field with Ω m gives the resulting field nside the interferometer or expressed by Bessel Functions: This gives the intensity on the photodiode: 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 functions of the first kind J0J0 J1J1 J2J2 J3J3 J4J4

9. In the Literature  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 gravitational wave detector, 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 http://www.ligo.caltech.edu/docs/P/P010005-00.pdf

10. Optical arrangement

12. Mechanical mode of the substrate 24 kHz

16. Scatterer simulations  Movement of the scatter source  Resulting noise spectrum

17. Shifting the scattered light to higher frequencies

18. Higher harmonics follow the Bessel functions

19. Deviation from optimal modulation index

20. Optical arrangement

21. Reducing the effect of scattered light