Optical characterization of ultrahigh diffraction efficiency gratings

Abstract

We report on the optical characterization of an ultrahigh diffraction efficiency grating in a first-order Littrow configuration. The apparatus used was an optical cavity built from the grating under investigation and an additional high-reflection mirror. The 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 Ϯ 0.016͒% 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.

Power-recycled michelson interferometer with a 50/50 grating beam splitter

“…that was resonant for this particular cavity length. Fig.8 shows the free spectral range of the power-recycling cavity of finesse F PR = 883 ± 28, which was used to determine optical loss inside the cavity [6]. Linear reference cavities built with the mirror combinations (M 0 , M PR ) and (M 1 , M PR ) showed an averaged finesse of F ref = 2543 ± 81.…”

“…Despite the fact that the absorption of the high-quality optics used can be as small as 0.25 ppm/cm [1] resulting thermal effects can still set a limit to the sensitivity of these detectors [2]. In all-reflective interferometer topologies [3,4,5,6] partly transmissive optics are replaced by reflection gratings. In addition to reducing all absorption related thermal effects inside the optics, all-reflective interferometers are capable of using opaque substrate materials and may thus benefit from their thermal and mechanical properties [7].…”

Lasers and optics: looking towards third generation gravitational wave detectors

“…The first demonstration was done in [70] where a cavity finesse of 53 was achieved. More recently, finesse values of up to ≈1,450 have been demonstrated [72]. The second concepts uses a so-called 2nd order Littrow arrangement.…”

Lateral input-optic displacement in a diffractive Fabry-Perot cavity

“…Prior work has found that state of the art gratings cannot achieve diffraction efficiencies approaching the reflection efficiencies available from multilayer dielectric coatings [6,7]. Thus Figure 1.…”