The first mid-infrared supermirrors have been developed by an international
team of researchers from Austria, the US, and Switzerland. These mirrors are
an essential component of many industrial laser cutting and welding systems,
as well as optical spectroscopy of greenhouse gases. The findings were just
released in the journal
Nature Communications.
In the realm of high-performance mirrors, the pursuit of flawless
reflectivity coatings is the stuff of legends. Advanced metal mirrors may
reach a reflectivity of up to 99% in the visible wavelength range
(wavelengths between 380 and 700 nm), which means that one photon is lost
for every 99 reflected photons. While it might sound like a lot, specialist
mirror coatings have previously achieved 99.9997% reflectivity in the
near-infrared band, which is about between 780 nm and 2.5 μm. This indicates
that just three reflected photons are lost out of a million.
The goal of this supermirror technology has always been to reach the
mid-infrared (wavelengths between 2.5 µm and 10 µm and beyond). This would
enable important advancements in several fields, such as the analysis of
biofuels and the measurement of trace gases linked to climate change.
Furthermore, a lot of industrial and medicinal uses, such laser scalpels and
cutting lasers, might be enhanced. The greatest mid-infrared mirrors
available today, however, lose one in 10,000 photons, which is around 33
times poorer than near-infrared supermirror performance.
An international group of scientists has now produced the first
mid-infrared supermirrors in the recently published study. The researchers
were able to create mirrors that only lose eight out of a million photons
thanks to the leadership of the Christian Doppler Laboratory for
Mid-Infrared Spectroscopy and Semiconductor Optics (CDL Mid-IR) at the
University of Vienna and the industrial partner Thorlabs Crystalline
Solutions (Santa Barbara, California). This indicates that the reflectivity
of these super mirrors is 99.99923%. The materials, the mirror design, and
the production process all required exact analysis and control on the part
of the researchers in order to set this record.
A novel coating technique was created.
The scientists had to create a new coating procedure first. They blended
cutting-edge semiconductor materials and processes with traditional
thin-film coating techniques. This allowed the material constraints in the
challenging mid-infrared region to be overcome. The head of the University
of Vienna's CDL Mid-IR, Oliver H. Heckl, stated, "This breakthrough shows
the enormous potential in successful collaboration between innovative basic
research and needs-oriented product development."
Thorlabs Crystalline Solutions (TCS) Technology Manager Garrett Cole says,
"This work builds on our pioneering work in substrate-transferred
crystalline coatings."
But manufacturing was only one aspect of the problem. To make certain that
the mirrors performed as promised, the scientists also had to measure them
carefully. The two initial authors, Gar-Wing Truong from TCS and Lukas
Perner from the University of Vienna, said that was their primary
responsibility. They add, "As co-inventors of this novel form of coating, it
was exciting to put these mirrors through their paces and thus confirm their
outstanding performance."
These new supermirrors have the immediate benefit of greatly increasing the
mid-infrared gas analysis optical device sensitivity. These instruments are
capable of precisely detecting and measuring minute concentrations of
significant environmental indicators, such carbon monoxide.
The team invited specialists from the National Institute of Standards and
Technology (NIST) to illustrate these potentials. They verified that the
mid-IR spectral range offers a significant advantage for ultrasensitive
spectroscopy, which includes the detection of radioisotopes crucial for
carbon dating and nuclear forensics.
Provided by
University of Vienna
