In scope of the ESA funded "High stability Laser" activity, a single-mode and single-frequency fiber power amplifier with 500 mW output power at 1064 nm wavelength has been developed. It is part of an elegant breadboard (EBB) which consists additionally of an ultra-stable Fabry-Perot reference for frequency stabilization. The monolithic fiber amplifier is seeded by a non-planar ring oscillator (NPRO) with a linewidth below 10 kHz. The amplifier is stabilized in power via pump diode modulation and achieves a RIN performance of <0.01/sqrt(Hz) in the range from 10(-3) Hz to 10 Hz and a polarization extinction ratio of >30 dB
Future space based missions for gravitational wave research call for an improved inertial reference sensor with acceleration noise levels of fm/s 2 . Spherical test masses can enable increased performance by suspension-free operation, contrary to cuboid solutions suffering from cross-coupling of attitude control noise. However, interferometric readout is affected by surface irregularities and test mass tumbling [1]. An accurate surface map for compensation must be established for compensation, either by characterisation a priori or in flight, when optical path length changes due to surface occur in the measurement band. We demonstrate a method for generating a surface map of a spherical body with optical point sensors using a differential method to suppress common mode errors present, taking advantage of the excellent performance of heterodyne interferometry at sub-nanometer levels. A measurement setup is proposed in which two beams of a Nd:YAG Michelson interferometer are used to scan the surface, which is afterwards reconstructed from the differential measurement. Such a method could potentially benefit other research areas, such as the precise determinations of the Avogadro constant [2] or aspheric surface metrology.
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