Transcript H.Lück - An acousto-optic phase 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.
 To be used in large diameter beams
Scatter
source
Mirror
Interferometer
beam

α
r= √(1-2)
the field in the interferometer
the field of the scattered beam
the resulting interfered beam
the power on a photodiode:
and the resulting in the spectrum:

Mirror
Interferometer
beam
Scatter
source

α
r= √(1-2)
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:
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
J0
J1
J2
J3
J4
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
Optical arrangement
Mechanical mode of the
substrate
24 kHz
Scatterer simulations
 Movement
of the
scatter source
 Resulting
spectrum
noise
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