A laser beam strikes a gold-and-silver film for just a few nanoseconds — in that time, light travels less than a meter. At the point of impact, the metal boils, splatters, and freezes into a random pattern of tiny particles. Each pattern is as unique as cracks in ice or tree branches. Deliberately reproducing it is impossible: the slightest jitter of the beam or a speck of dust changes the picture.
These particles act as miniature antennas: light of a specific color makes them resonate, and the reflected signal becomes bright and recognizable. Shine red, green, and blue lasers on the tag, and you get three different responses. Thus, a single pattern becomes several keys at once, as if one lock could be opened with three different turns. The capacity of such a key is about 28,000 bits, more than a standard QR code.
The laser-made keys are resistant to moisture, heat, and scratches. They can be applied directly to plastic, glass, or metal without chemicals or masks. This simplicity paves the way for mass protection: from bank cards to drug packaging, where distinguishing the original from a fake is critical.
A single square millimeter of such a tag can store more random information than needed to uniquely label every person on Earth.
In the series Westworld, androids carry hidden optical tags for identification — laser plasmonic keys could be a real-world prototype of such technology.