Infrared light with a wavelength of about three micrometers is the working range for identifying molecules: each molecule absorbs light at its own characteristic frequencies, leaving behind "fingerprints." But until now, instruments for this range could not simultaneously provide broad frequency coverage, sufficient power, and precision tied to atomic standards.

The new system uses two near-infrared lasers whose frequencies are precisely tracked against atomic clocks. Their beams are mixed in a special crystal, producing mid-infrared light tunable from 3 to 3.7 micrometers. The power exceeds 45 milliwatts, and the absolute frequency accuracy is 7.2 megahertz, comparable to the width of a gas spectral line.

This precision helped resolve a long-standing issue in photonic chips: light absorption caused by hydrogen atoms that get into silicon nitride. Losses were reduced by a factor of 88. It also turned out that the fundamental limit for the mid-infrared range in integrated photonics is set by absorption from atomic vibrations in the silica glass cladding.

The second demonstration is a lidar that not only measures the distance to a target but also determines its chemical composition, even through optically thick fog. This opens the way to machine vision systems that "see" not just the shape but also the material of an object in adverse weather.