Measuring vibrations using Doppler shifted frequency modulated continuous-wave LIDAR with single photons

We demonstrate a <i>frequency modulated continuous-wave</i> (FMCW) light detection and ranging (LIDAR) system utilizing a <i>superconducting nanowire single-photon detector</i> (SNSPD) to measure vibrational spectra using reflected signals at the single-photon level. By determining the time-variant Doppler shift of the reflected probe signal, this system successfully reconstructs various audio signals, including pure sinusoidal, multi-tonal, and musical signals, up to 200 Hz, limited by the laser frequency modulation rate and the Nyquist sampling theorem. Additionally, we employ scanning galvo mirrors to perform 3D measurements and map audio signals from different regions in the scanned field of view. The integration of an SNSPD provides significant advantages such as near-unity detection efficiency, low dark count rates, and picosecond timing jitter, enabling measurements of vibrational spectra with as few as 100 detected reflected photons per laser sweep.