Manipulation of photonic orbital-angular-momentum phase spectrum for high-accuracy rotating velocimetry of a posture-varied target

Rotating Doppler velocimetry of a target has gained huge development in decade, from the initially required alignment between optical and rotary axes to lateral and angular deviations of them. However, signal-to-noise ratio (SNR) and measured error are still salient for rotating velocimetry of an arbitrary pose-varied target, especially when the deviations (including lateral or/and angular conditions) inevitably exist. Here, we proposed and demonstrate a feed-back compensation scheme for overcoming these difficulties, based upon measuring and manipulating orbital-angular-momentum (OAM) phase spectrum. The conjugate OAM superposed states are firstly launched to a rotating surface with lateral or/and angular deviations and then we measure the OAM complex spectrum and rotating Doppler spectrum of the echo photons, respectively. We further modulate the measured specific OAM phase spectrum components and combine the original OAM amplitude spectrum to reconstruct the updated emitted light on a diffractive phase element. In doing so, the measured SNR and the accuracy of the rotating Doppler velocimetry are gradually improved. As a consequence, we thus develop a high-sensitive and high-accuracy rotating Doppler velocimeter This laboratory-constructed prototype might be additionally pushed for applications in astrophysics, industrial manufacturing and meteorological monitoring, etc.