Crystalline Mirror Solutions


Ultralow loss mid-IR optics
ppm-level optical losses

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    Center wavelength

    2 µm

    5 µm

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    Optical losses

    < 10 ppm (scatter + absorption)

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    200 nm FWHM

    400 nm FWHM



Optical transmission
Tunable, per customer request
Coating material
Single-crystal GaAs/AlGaAs
Substrate material
Typically single-crystal silicon, other materials possible
Substrate diameter
0.5 - 1 inch (12.7 - 25.4 mm), other sizes available
Radius of curvature (ROC)
>0.1 m
Surface flatness
<0.10 wave P-V measured @ 633 nm
Surface quality
<5 Å RMS micro-roughness
Similar to fused silica, cleaning instructions provided on request

Trace Gas Sensing

The potential for unprecedentedly low optical losses in the MIR spectral regime opens up completely new application areas relevant to long-wavelength lasers and spectroscopy systems, with potential highlights being devices for medical and environmental monitoring. High-performance MIR optics are of significant interest as many large molecules important for atmospheric science, medicine, and national security have fundamental ro-vibrational transitions in this region. Cavity enhanced detection methods provide the highest sensitivity and low-loss optics based on crystalline mirror technology are yielding a significant improvement in the capabilities of such MIR sensing systems. Recently, the first prototype MIR crystalline mirrors demonstrated optical performance on par with the best dielectric coatings present on the commercial market.

Relevant publications

  • Direct frequency comb measurement on OD + CD -> DOCO kinetics

    B. J. Bjork, T. Q. Bui, O. H. Heckl, P. B Changala, B. Spaun, P. Heu, D. Follman, C. Deutsch, G. D. Cole, M. Aspelmeyer, M. Okumura, J. Ye.

    "Direct frequency comb measurement on OD + CD -> DOCO kinetics," Science, Vol. 354, Issue 6311, 444-448, 28 Oct 2016. DOI: 10.1126/science.aag1862

    The kinetics of the hydroxyl radical (OH) + carbon monoxide (CO) reaction, which is fundamental to both atmospheric and combustion chemistry, are complex because of the formation of the hydrocarboxyl radical (HOCO) intermediate. Despite extensive studies of this reaction, HOCO has not been observed under thermal reaction conditions. Exploiting the sensitive, broadband, and high-resolution capabilities of time-resolved cavity-enhanced direct frequency comb spectroscopy, we observed deuteroxyl radical (OD) + CO reaction kinetics and detected stabilized trans-DOCO, the deuterated analog of trans-HOCO. By simultaneously measuring the time-dependent concentrations of the trans-DOCO and OD species, we observed unambiguous low-pressure termolecular dependence of the reaction rate coefficients for N2 and CO bath gases. These results confirm the HOCO formation mechanism and quantify its yield.

  • High-performance near- and mid-infrared crystalline coatings

    G. D. Cole, W. Zhang, B. J. Bjork, D. Follman, P. Heu, C. Deutsch, L. Sonderhouse, J. Robinson, C. Franz, A. Alexandrovski, M. Notcutt, O. H. Heckl, J. Ye, M. Aspelmeyer

    "High-performance near- and mid-infrared crystalline coatings," Optica, Vol. 3, No. 6, 647-656, June 2016.

    Substrate-transferred crystalline coatings have recently emerged as a groundbreaking new concept in optical interference coatings. Building upon our initial demonstration of this technology, we have now realized significant improvements in the limiting optical performance of these novel single-crystal GaAs/Al𝑥Ga 1−𝑥 As multilayers. In the near-infrared (NIR), for coating center wavelengths spanning 1064–1560 nm, we have reduced the excess optical losses (scatter + absorption) to levels as low as 3 parts per million (ppm), enabling the realization of a cavity finesse exceeding 3×10^5 at the telecom-relevant wavelength range near 1550 nm. Moreover, we demonstrate the direct measurement of sub-ppm optical absorption at 1064 nm. Concurrently, we investigate the mid-infrared (MIR) properties of these coatings and observe exceptional performance for first attempts in this important wavelength region. Specifically, we verify excess losses at the hundred ppm level for wavelengths of 3300 and 3700 nm. Taken together, our NIR optical losses are now fully competitive with ion-beam sputtered multilayer coatings, while our first prototype MIR optics have already reached state-of-the-art performance levels for reflectors covering this portion of the fingerprint region for optical gas sensing. Mirrors fabricated with our crystalline coating technique exhibit the lowest mechanical loss, and thus the lowest Brownian noise, the highest thermal conductivity, and, potentially, the widest spectral coverage of any “supermirror” technology in a single material platform. Looking ahead, we see a bright future for crystalline coatings in applications requiring the ultimate levels of optical, thermal, and optomechanical performance.