LIGO Document T1800200-v7

In-Situ Laser Mode Spectroscopy for Mirror Phase Mapping

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T - Technical notes
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This project is focused on improving the sensitivity in LIGO by characterizing mirror figure error that contributes to optical losses in the laser. As a result of scattered light, optical losses increase shot noise and destroy the squeezed state of light. Surface perturbations in the mirrors will be evaluated with In-Situ laser mode spectroscopy using the 40 meter prototype laser interferometer gravitational wave detector. Mirror figure error will cause the resonant frequencies of the Hermite-Gaussian modes to shift from their ideal theoretical spacings. Mirror phase maps, a physical representation of the mirror, can be reconstructed by analyzing the shift in mode spacings with Bayesian inference. The success of aLIGO is largely due to precise optical measurements. By mapping the surface of the mirror down a precision of 1 Angstrom, the optical losses and noise can be evaluated and minimized.
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