Mid-infrared interference coatings with excess optical loss below 10  ppm

Abstract

We present high-reflectivity substrate-transferred single-crystal GaAs/AlGaAs interference coatings at a center wavelength of 4.54 µm with record-low excess optical loss below 10 parts per million. These high-performance mirrors are realized via a novel microfabrication process that differs significantly from the production of amorphous multilayers generated via physical vapor deposition processes. This new process enables reduced scatter loss due to the low surface and interfacial roughness, while low background doping in epitaxial growth ensures strongly reduced absorption. We report on a suite of optical measurements, including cavity ring-down, transmittance spectroscopy, and direct absorption tests to reveal the optical losses for a set of prototype mirrors. In the course of these measurements, we observe a unique polarization-orientation-dependent loss mechanism which we attribute to elastic anisotropy of these strained epitaxial multilayers. A future increase in layer count and a corresponding reduction of transmittance will enable optical resonators with a finesse in excess of 100 000 in the mid-infrared spectral region, allowing for advances in high resolution spectroscopy, narrow-linewidth laser stabilization, and ultrasensitive measurements of various light-matter interactions.

A high-power-handling deformable mirror system employing crystalline coatings

“…To-date, our record performance level is an optical absorption below 1 ppm and scatter < 2 ppm, enabling a cavity finesse > 700,000 (R > 99.9995%) in the near-IR spectral region with our crystalline mirrors. It is worth noting that this level of performance (S+A < 5 ppm) can be maintained out to a center wavelength of 5000 nm with our crystalline coating technology [14,15]. Additionally, owing to their single-crystal nature, these coatings have a well controlled stress state (defined by the lattice mismatch and independent of deposition conditions) and a relatively high thermal conductivity, 20-30 Wm -1 K -1 through the thickness of the multilayer (interface scattering limited) and up to 70 Wm -1 K -1 in plane.…”

Dual-comb cavity ring-down spectroscopy

“…Potential applications include the accurate measurement of critical reference data to enable the identification of natural gas leaks 45 and precision radiative transfer and climate change models 46 – 49 , as well as the evolution of methane and oxygen line shapes relevant to the search for exoplanet companion biosignatures 50 , 51 . Other potential applications of DC-CRDS include non-invasive optical sensors to probe complex gas matrices such as breath 6 , 52 , as well as agile multispecies trace gases analyzers for atmospheric composition monitoring 53 – 55 , characterization of broadband mirror loss and dispersion 37 , 56 , chemical reaction kinetics 8 and collisional processes in gases 57 . Finally, DC-CRDS could bring all the advantages of CRDS to the frontier of research on high-resolution broadband spectroscopy of cold large organic molecules 58 and other complex molecular systems 59 .…”

Optical Feedback Linear Cavity Ringdown Spectroscopy

“…It leverages an optical cavity to prolong the interaction length between the laser and the intracavity gas, and thus, an amplified absorption signal can be obtained. With superior coating technologies, the amplification factor larger than 10 5 and the detection sensitivity for trace gas detection down to 10 −13 cm −1 could be achieved [9,10]. On the other hand, CRDS deduces the intracavity absorption information from the variation of the ringdown times, rather than the amplitudes of the cavity transmission modes.…”