A warm cup or a human hand emits invisible light — mid-infrared radiation. Every substance absorbs this light in its own way, leaving a unique 'fingerprint'. From this fingerprint, you can tell what an object is made of without touching it.
Previously, seeing this fingerprint required huge lasers that fired very short pulses. They were expensive and complex. The new setup uses a laser with longer pulses — nanosecond ones. Such a laser is more compact and simpler. Its light hits an ordinary camera that is sensitive to the near-infrared range. Thanks to a clever trick, two-photon absorption, the camera 'sees' mid-infrared light even though it wasn't designed for it.
The researchers obtained video at several frames per second for the first time in the range where many molecules have their fingerprints. This means you can watch chemical processes live: how paint dries, how a drug distributes in a tablet, or how the composition of plastic changes when heated.
Now such a device can be assembled on an ordinary table. It paves the way for cheap and fast chemical analysis systems for factories, hospitals, and laboratories.
The mid-infrared range is sometimes called the 'fingerprint region' of molecules because each molecule absorbs light at its own specific wavelengths, like a unique pattern on a finger.