Capturing an elusive spectrum of light

Researchers led by EPFL have built ultra-high quality optical cavities for the elusive mid-infrared spectral region, paving the way for new chemical and biological sensors, as well as promising technologies. The mid-infrared spectral window, referred to as 'molecular fingerprint region,' includes light wavelengths from 2.5 to 20 'm. It is a virtual goldmine for spectroscopy, chemical and biological sensing, materials science, and industry, as it is the range where many organic molecules can be detected. It also contains two ranges that allow transmission of signals through the atmosphere without distortion or loss. A way to harness the potential of the mid-infrared spectral window is to use optical cavities, which are micro-devices that confine light for extended amounts of time. However, such devices are currently unexplored due to technological challenges at this wavelength. Researchers led by EPFL have taken on this challenge and successfully shown that crystalline materials can be used to build ultra-high quality optical cavities for the mid-infrared spectral region, representing the highest value achieved for any type of mid-infrared resonator to date and setting a new record in the field.