Erlangen 2018 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 58: Precision Measurements and Metrology (Gravity and Miscellaneous) (joint session Q/A)

Q 58.5: Talk

Thursday, March 8, 2018, 11:30–11:45, K 2.013

Thickness uniformity measurements of crystalline AlGaAs mirror coatings — •Philip Koch — MPI für Gravitationsphysik, Hannover, Deutschland

Beside quantum noise, the sensitivity of the current generation of gravitational wave detectors is limited by coating Brownian noise of the interferometer mirrors. This arises from thermal fluctuations of the molecules in the coating itself. Coating Brownian noise is dependent on the mechanical loss angle of the coating materials. AlGaAs mirror coatings are crystalline dielectric coatings which have higher Q factors (lower loss) and thus a ten-fold reduction of coating Brownian noise compared to the commonly used amorphous silica-tantala coatings. A homogenous surface figure is needed in the high precision interferometry to avoid optical losses. A method to measure the surface homogeneity of mirror coatings will be presented with an accuracy of below 0.05 nm. This method was used to measure a 0.5 nm RMS thickness homogeneity across a 5 cm diameter AlGaAs coating provided by Crystalline Mirror Solutions.