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Physics, Optics, physics.optics
Abstract:
Crystalline silicon has been proposed as a new test mass material in third
generation gravitational wave detectors such as the Einstein Telescope (ET).
Birefringence can reduce the interferometric contrast and can produce dynamical
disturbances in interferometers. In this work we use the method of
polarisation-dependent resonance frequency analysis of Fabry-Perot-cavities
containing silicon as a birefringent medium. Our measurements show a
birefringence of silicon along the (111) axis of the order of $\Delta\, n
\approx 10^{-7}$ at a laser wavelength of 1550nm and room temperature. A model
is presented that explains the results of different settings of our
measurements as a superposition of elastic strains caused by external stresses
in the sample and plastic strains possibly generated during the production
process. An application of our theory on the proposed ET test mass geometry
suggests no critical effect on birefringence due to elastic strains.
