Free-space remote detection of a spinning object using the combined vortex beam

The rotational Doppler effect (RDE) associated with orbital angular momentum (OAM) has been used for remote sensing of a spinning object. However, one of the challenges of long-range detection stems from the low echo signal power. In this paper, we propose a new detection scheme that uses the combined vortex beam (CVB) generated by coherent beam combining (CBC) technology as the probe beam to enhance the echo signal power. Furthermore, we establish a rotational speed remote sensing model based on RDE, the emitted power and emission diameter of the probe beam are investigated in detail. The results show that, compared with the superposition vortex beam (SVB) generated by a single laser beam, the CVB detection scheme can significantly enhance the echo signal intensity and detection distance. The measuring range and accuracy of rotational speed are also studied in detail. And finally, we present the first experimental demonstration of the RDE arising directly from the interaction of the CVB with a rotating rough surface. The scheme proposed in our paper offers a good reference for practical application of the remote detection based on RDE.