A piano tuner in a noisy hall doesn't listen to all sounds indiscriminately: they isolate one string among dozens. A similar challenge is tackled by the new laser radar: among the many reflected beams, it identifies those carrying information about the target's vibration.
A conventional radar sends a short pulse and waits for the echo. But if the object is vibrating, the echo becomes blurred. The authors of the study mixed the reflected light with a reference beam on a detector array, as if each piano string had its own microphone. This allowed them to extract weak oscillations even from strong interference.
Such a radar could be used to monitor bridges and buildings: cracks and weak spots reveal themselves through barely perceptible trembling. Or to identify drones by the vibration signature of their motors.
The human ear can detect air vibrations with amplitudes smaller than the diameter of a hydrogen atom, the new radar demonstrates similar sensitivity for light.
In the series 'The Expanse,' ships are detected by the heat signature of their engines; this radar could catch them by the vibration of their hulls.