Single-photon LiDAR interferometry for lateral velocity measurement

Accurately retrieving the lateral velocity of distant, non-cooperative targets under photon-starved conditions has remained a longstanding challenge, as conventional imaging or tracking methods often fail in the absence of stable illumination or resolvable features. We present a single-photon light detection and ranging (LiDAR) interferometric scheme that actively illuminates the target and measures its motion-induced optical path difference variations across spatially separated receivers. A complete theoretical framework is developed, which establishes the system's sensitivity limit and predicts the minimum detectable photon number. Simulations and experiments demonstrate that the method achieves micron-level spatial resolution and millimeter-per-second velocity precision with as few as ∼200 detected photons per single measurement, and remains effective over kilometer-scale free-space links. The approach is robust to non-cooperative targets, enabling high-precision velocity sensing in extremely low-light environments. By integrating with single-photon ranging, it can deliver full 3D velocity vectors, extending the operational envelope of LiDAR for space surveillance, collision avoidance, and precision motion sensing.