Abstract
Waveguide mirrors (WGMs) possess nano-structured surfaces which can potentially provide a significant reduction in thermal noise over conventional dielectric mirrors. To avoid introducing additional phase noise from the motion of the mirror transverse to the reflected light, however, they must possess a mechanism to suppress the phase effects associated with the incident light translating across the nano-structured surface. It has been shown that with carefully chosen parameters this additional phase noise can be suppressed. We present an experimental measurement of the coupling of transverse to longitudinal displacements in such a WGM designed for 1064 nm light. We place an upper limit on the level of measured transverse to longitudinal coupling of one part in seventeen thousand with 95% confidence, representing a significant improvement over a previously measured grating mirror.
Highlights
Major upgrades to the worldwide network of gravitational wave detectors are currently under way
New designs for the Advanced LIGO [1], Advanced Virgo [2], KAGRA [3] and GEO-HF [4] detectors will provide unmatched ability to detect gravitational waves in the audio spectrum. At their most sensitive frequencies, these detectors are expected to be limited by Brownian thermal noise arising from the reflective coatings on the detectors’ test masses [5,6,7,8]
In order to help mitigate this limitation beyond the generation of detectors, efforts are under way to develop mirror coatings with lower thermal noise [9, 10]
Summary
Major upgrades to the worldwide network of gravitational wave detectors are currently under way. The second mechanism is the coupling of changes in the opposite cavity mirror’s alignment into the spot position on the grating mirror This effect is of particular importance to gravitational wave observatories, where longer arm lengths can increase its detrimental impact. In order to quantify its transverse coupling, a WGM was produced in collaboration with Friedrich-Schiller University Jena, Germany (see Table 1 for its properties) It was designed for light of wavelength 1064 nm, and consisted of an etched grating structure on top of a waveguide layer, both tantala, on a z α βm y ζa ζb δy Figure 2: Optical path length changes ζa and ζb due to transverse motion of a Littrow grating. This article details an experiment carried out to measure its transverse coupling level
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