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.  To be used in large diameter beams

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

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:

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

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:

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:

Bessel functions of the first kind J0J0 J1J1 J2J2 J3J3 J4J4

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  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  P. Beyersdorf 2001 The polarization Sagnac Interferometer for gravitational Wave Detection, PhD thesis

Optical arrangement

Mechanical mode of the substrate 24 kHz

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

Shifting the scattered light to higher frequencies

Higher harmonics follow the Bessel functions

Deviation from optimal modulation index

Optical arrangement

Reducing the effect of scattered light