Photon-Counting 3D Velocimetry Empowered by OAM-Based Multi-Point Doppler Effect

Velocimetry of a motion target within 3-D space is highly desirable in numerous applicable realms, ranging from explosion and shock wave physics, aerospace engineering to astronomical surveys. However, it is challenging to achieve synchronous, real-time, and photon-counting 3-D velocimetry in modern frameworks as they either require separate multi-directional detections, and cumbersome calculation processes or are confined to achieve in situ measurements. Here, a new conceptual paradigm is proposed to circumvent these constraints using orbital-angular-momentum (OAM)-driven multi-point Doppler effect at the photon-counting level. This scheme, emanating from a single-direction launch of an on-demand engineered sequence OAM light mode onto a motion surface, enables simultaneous and independent detections of time-varying Doppler photon-count events from three orthogonal echo light paths. Concretely, at the range of motion velocity of 0.25–0.5 ms⁻¹, the relative measurement errors of this proof-of-principle prototype are below 1.5%, thus achieving high-accuracy 3-D velocimetry at the photon-counting level for the first time. The exploration of the OAM-photon-counting 3-D velocimetry techniques provides unprecedented advantages in potential applications of synchronous, real-time, high-efficiency, and long-range quantum lidar.