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Free keywords:
Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM, Physics, Optics, physics.optics
Abstract:
The arm length and the isolation in space enable LISA to probe for signals
unattainable on ground, opening a window to the sub-Hz gravitational-wave
universe. The coupling of unavoidable angular spacecraft jitter into the
longitudinal displacement measurement, an effect known as tilt-to-length (TTL)
coupling, is critical for realizing the required sensitivity of
picometer$/\sqrt{\rm{Hz}}$. An ultra-stable interferometer testbed has been
developed in order to investigate this issue and validate mitigation strategies
in a setup representative of the LISA long-arm interferometer. We demonstrate a
reduction of TTL coupling between a flat-top beam and a Gaussian beam via
introducing two- and four-lens imaging systems. TTL coupling factors below $\pm
25\,\mu$m/rad for beam tilts within $\pm 300\,\mu$rad are obtained by careful
optimization of the system. Moreover we show that the additional TTL coupling
due to lateral alignment errors of elements of the imaging system can be
compensated by introducing lateral shifts of the detector, and vice versa.
These findings help validate the suitability of this noise-reduction technique
for the LISA long-arm interferometer.
