Merging compound semiconductor technology
with precision optics
High-reflectivity optical coatings are key components for a wide variety of laser-based applications. With the continuing progress in laser development, state-of-the-art optical coatings have now become a major limitation for various applications in the domain of precision measurement and instrumentation.
Substrate-transferred crystalline coatings represent a game-changing technology that enables the integration of single-crystal films onto arbitrary, including curved, optical substrates, exploiting, for the first time, the unique properties of monocrystalline semiconductor materials for high-performance laser optics. This technological breakthrough was long due and awaited since the 1970s to increase performance levels in existing applications and the development of new applications in high precision measurements.
This technology results in Semiconductor Supermirrors with 3 key advantages:
measurements of space and time
Ultra-precise measurements of space and time
Using our technology, we can construct optical cavities capable of significantly improved thermal noise performance. Mirror assemblies produced with our coating technology offer up to a 10x reduction in thermo-mechanical (i.e., Brownian) noise compared to current state-of-the-art technology. We have demonstrated this unique thermal noise performance in collaboration with the Ye group at NIST/JILA (1). This substantial reduction in thermal fluctuations enables a significant improvement in the overall frequency stability of optical reference cavities, pushing the ultimate limits of linewidth and noise performance that can be achieved in stabilized laser systems. Given the fact that the last 15 years of research into the coating noise problem had only yielded a reduction by a factor of two, these results represent a long-awaited breakthrough for the precision measurement community. In addition, there are presently no viable alternatives that can achieve such low levels of thermal noise, while maintaining sufficient optical performance.
in trace gas sensing
High resolution in trace gas sensing
For the past decades, IBS-deposited dielectric multilayers have been the most commonly used materials systems for low-loss mirrors in the NIR. One major limitation for these materials is significant levels of optical absorption for wavelengths beyond ~2 μm, which excludes operation of such low-loss reflectors in the mid-infrared (MIR). Compared to dielectric materials, AlGaAs-based DBRs can achieve much lower optical losses in the important spectral mid-IR region between 2 and 5 μm, with absorption losses below 10 ppm. In first tests using substrate-transferred semiconductor materials, performed in the Ye group at JILA/NIST, a cavity with a finesse exceeding 10,000 was demonstrated, while simultaneously exhibiting a cavity reflection contrast of 71%.
for high-power lasers
High thermal conductivity for high-power lasers
High-power lasers, which are used for a large number of industrial applications, are limited by the unavoidable residual absorption of the reflective optics being used in the lasers system. The low thermal conductivity of IBS coatings (in the order of 1 W/(m*K)) drastically limits the effectiveness of any heat sink solution and attempts to avoid heat-induced structural damage in both the coating and laser system. AlGaAs-based DBRs show a thermal conductivity at least 30x greater than in traditionally sputtered coatings. This significant performance increase makes substrate-transferred crystalline mirrors an ideal optical system for superior thermal management in harsh environments. Additionally, the intrinsic bonding process allows integration of the DBR onto arbitrary substrates, particularly for high-power optical applications, high-performance SiC or diamond substrates used as heat sinks.
Coating and Production Technology
Using Molecular Beam Epitaxy (MBE), the highest-quality single crystal GaAs/AlGaAs multilayer is grown to create a reflector coating with an engineered reflectivity, typically greater than 99.99%. In the near-IR, scattering + absorption losses can be <5 ppm. The coating is precisely defined in any arbitrary shape using semiconductor processing technology and then removed from the GaAs growth wafer as a precursor to direct bonding.
Our experience and proprietary direct bonding process enables dissimilar materials to be permanently bonded with no interlayers or solders. The result: The best mirror possible on the ideal substrate.