An ordinary laser emits a single color, like a single note on a piano. But to find molecules in the air, you need an instrument that quickly sweeps across many colors, like a musician playing a scale. Such a laser is called tunable, and the faster it changes color, the faster you can 'sniff' the air. The problem is that at high speeds, the laser starts to go out of tune: its color jumps off target, and measurements become messy.

Scientists figured out how to bring order. They took two tiny glass rings — microresonators. The first ring works as a ruler: it creates a very even grid of frequencies against which you can check exactly where the laser has landed. The second ring, with high quality factor, captures the instantaneous color of the laser and shows how blurred it is. Together, they allow correcting the laser's errors in real time, much like a tuning fork and a tuner help a piano tuner.

After correction, the laser measured methane with an accuracy of 9 parts per billion per meter per second. That's like finding a single grain of sand in an Olympic-sized swimming pool. Moreover, the device can even distinguish methane isotopes — molecules with different weights of carbon atoms. And the system works even when the light is attenuated by 78 decibels, meaning it is almost completely lost along the way.

Such a laser 'sniffer' will be useful for detecting gas leaks, monitoring air in factories, and even for medical diagnostics via breath analysis. Instead of building huge and expensive setups, you could use compact chips with glass rings, and get precise maps of invisible gases.