Optical characterization of ultra-high diffraction efficiency gratings

TL;DR

This paper presents the optical characterization of an ultra-high diffraction efficiency grating using a cavity finesse measurement, demonstrating near-perfect efficiency and minimal optical loss, with potential applications in gravitational wave detection.

Contribution

It introduces a novel cavity-based method to precisely measure the diffraction efficiency and optical loss of ultra-high efficiency gratings.

Findings

Diffraction efficiency of 99.635% measured

Optical loss due to scattering and absorption is 0.185%

Finesse of the cavity is 1580

Abstract

We report on the optical characterization of an ultra-high diffraction efficiency grating in 1st order Littrow configuration. The apparatus used was an optical cavity built from the grating under investigation and an additional high reflection mirror. Measurement of the cavity finesse provided precise information about the grating's diffraction efficiency and its optical loss. We measured a finesse of 1580 from which we deduced a diffraction efficiency of (99.635$\pm$0.016)% and an overall optical loss due to scattering and absorption of just 0.185 %. Such high quality gratings, including the tool used for their characterization, might apply for future gravitational wave detectors. For example the demonstrated cavity itself presents an all-reflective, low-loss Fabry-Perot resonator that might replace conventional arm cavities in advanced high power Michelson interferometers.