title: Pound-Drever-Hall error signals for the length control of three-port grating coupled cavities.
abstract: Gratings enable light coupling into an optical cavity without transmission through any substrate. This concept reduces light absorption and substrate heating and was suggested for light coupling into the arm cavities of future gravitational wave detectors. One particularly interesting approach is based on all-reflective gratings with low diffraction efficiencies and three diffraction orders (three ports). However, it was discovered that, generally, three-port grating coupled cavities show an asymmetric resonance profile that results in asymmetric and low quality Pound-Drever-Hall error signals for cavity length control. We experimentally demonstrate that this problem is solved by the detection of light at both reflection ports of the cavity and the postprocessing of the two demodulated electronic signals.
authors.affiliation: Albert-Einstein-Institut, Max-Planck-Institut für Gravitationsphysik and Leibniz Universität Hannover, Hannover, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Britzger
authors.forename: Daniel
authors.initials: D
authors.lastname: Friedrich
authors.forename: Stefanie
authors.initials: S
authors.lastname: Kroker
authors.forename: Frank
authors.initials: F
authors.lastname: Brückner
authors.forename: Oliver
authors.initials: O
authors.lastname: Burmeister
authors.forename: Ernst-Bernhard
authors.initials: EB
authors.lastname: Kley
authors.forename: Andreas
authors.initials: A
authors.lastname: Tünnermann
authors.forename: Karsten
authors.initials: K
authors.lastname: Danzmann
authors.forename: Roman
authors.initials: R
authors.lastname: Schnabel