A Quest for Perfection: Breakthrough in Mid-Infrared Mirror Technology Achieves Unprecedented 99.99923% Reflectivity

In a collaborative international endeavor detailed in the pages of Nature Communications, a remarkable milestone has been reached in the realm of mirror technology. Researchers from the United States, Austria, and Switzerland have successfully pioneered the creation of mid-infrared supermirrors boasting an astonishing 99.99923% reflectivity. This achievement is poised to revolutionize environmental gas sensing and industrial processes, signifying a monumental advancement in the field of mirrors. Credit: SciTechPost.com

Elevating Precision in Infrared Mirrors for Environmental and Industrial Applications

A multi-national team of scientists hailing from the United States, Austria, and Switzerland has introduced a groundbreaking development in mid-infrared supermirrors. These supermirrors hold immense significance across various domains, including optical spectroscopy for environmental sensing and applications like laser cutting and welding for industrial manufacturing.

Attaining Near-Perfection in Reflectivity

Within the realm of high-performance mirrors, the pursuit of perfection is an enduring quest. In the visible spectrum, advanced metallic mirrors achieve reflectivity rates as high as 99%, signifying the loss of merely one photon for every 99 reflected. While this achievement is indeed impressive, in the near-infrared spectrum, mirror coatings have already demonstrated an extraordinary 99.9997% reflectivity, with just three photons lost out of every million reflected.

The aspiration has long been to extend this supermirror performance into the mid-infrared range, spanning wavelengths from 2.5 µm to 10 µm and beyond. This extension holds promise for improving trace gas sensing in relation to climate change and biofuels, as well as for enhancing industrial applications such as laser machining and nanofabrication. Until now, mid-infrared mirrors have lagged behind, losing approximately one out of every 10,000 photons, which is approximately 33 times less efficient than their near-infrared counterparts.

International Collaboration Yields a Breakthrough

As elucidated in the article published in Nature Communications, an international consortium of researchers from Thorlabs’ Crystalline Solutions in Santa Barbara, CA, the Christian Doppler Laboratory for Mid-Infrared Spectroscopy at the University of Vienna in Austria, the U.S. National Institute of Standards and Technology (NIST), and the University of Neuchâtel in Switzerland has achieved a momentous milestone by introducing the world’s first genuine mid-infrared supermirrors. These supermirrors only forfeit eight photons out of every million, achieving an exceptional reflectivity of 99.99923%. The attainment of such unparalleled reflectivity necessitated a combination of expertise in materials, mirror design, and manufacturing techniques.

A Novel Approach to Mirror Coatings

To realize this pioneering generation of mid-infrared supermirrors, the research team devised and demonstrated a novel approach to coatings. They ingeniously merged conventional thin-film coating methods with innovative semiconductor materials and techniques to surmount the inherent challenges of the mid-infrared spectrum.

Garrett Cole, the Technology Manager of Thorlabs’ Crystalline Solutions team, elucidated, “This endeavor builds upon our trailblazing work in substrate-transferred crystalline coatings. Expanding this platform into longer wavelengths, our international collaboration has become the first to unveil a mid-infrared coating method characterized by absorption and scatter losses of less than 5 parts per million.”

Leveraging the outstanding structural quality of molecular beam epitaxy, a sophisticated process employed in the manufacture of various semiconductor devices, the researchers generated monocrystalline GaAs/AlGaAs multilayers virtually devoid of absorption and scatter. This initial material was subsequently transformed into high-performance mirrors using advanced microfabrication techniques, including direct “fusion” bonding onto high-quality conventional non-crystalline thin-film interference coatings developed at the University of Neuchâtel.

Precise Measurement Validates Superior Performance

The fabrication of these groundbreaking mirrors was only half the challenge. Rigorous measurements were imperative to validate their superior performance. Gar-Wing Truong, the Lead Scientist at Thorlabs Crystalline Solutions, noted, “It was an immense collaborative effort to assemble the requisite equipment and expertise to conclusively demonstrate total losses as low as 7.7 parts per million, a level six times superior to any conventional mid-infrared coating technique achieved thus far.”

Lukas Perner, a co-lead author and Scientist at the University of Vienna, added, “As a co-inventor of this innovative coating paradigm, it was both thrilling and gratifying to subject these supermirrors to rigorous testing. Our collective endeavors in pioneering mirror technology and employing advanced characterization methods have culminated in the unveiling of their extraordinary performance, heralding a new era in the mid-infrared spectrum.”

Implications for Environmental Sensing and Spectroscopy

One immediate application of these innovative mid-infrared supermirrors is their potential to significantly enhance the sensitivity of optical devices used to measure trace amounts of gases. Cavity ringdown spectrometers (CRDS), capable of detecting and quantifying minuscule quantities of critical environmental markers such as carbon monoxide, stand to benefit immensely from this advancement. In a proof-of-concept experiment that subjected these supermirrors to rigorous testing, NIST research chemists Adam Fleisher and Michelle Bailey showcased their superior performance, surpassing current state-of-the-art technologies.

Michelle Bailey stated, “Low-loss mirrors facilitate the achievement of remarkably extended optical pathlengths within compact devices. In this context, it’s akin to compressing the distance between Philadelphia and NYC into a single meter. This constitutes a pivotal advantage for ultra-sensitive spectroscopy in the mid-infrared spectrum, including the measurement of radioisotopes, which hold significance in nuclear forensics and carbon dating.”

Reference: “Mid-infrared supermirrors with finesse exceeding 400 000” by Gar-Wing Truong, Lukas W. Perner, D. Michelle Bailey, Georg Winkler, Seth B. Cataño-Lopez, Valentin J. Wittwer, Thomas Südmeyer, Catherine Nguyen, David Follman, Adam J. Fleisher, Oliver H. Heckl, and Garrett D. Cole, 6 December 2023, Nature Communications.
DOI: 10.1038/s41467-023-43367-z

Frequently Asked Questions (FAQs) about Mid-infrared supermirrors

More about Mid-infrared supermirrors

• Nature Communications Article
• Thorlabs’ Crystalline Solutions
• University of Vienna – Christian Doppler Laboratory for Mid-Infrared Spectroscopy
• U.S. National Institute of Standards and Technology (NIST)
• University of Neuchâtel
• Cavity Ringdown Spectrometers (CRDS)