Detection of a Spinning Object at Different Beam Sizes Based on the Optical Rotational Doppler Effect

Abstract

The rotational Doppler effect (RDE), as a counterpart of the conventional well-known linear Doppler effect in the rotating frame, has attracted increasing attention in recent years for rotating object detection. However, the effect of the beam size on the RDE is still an open question. In this article, we investigated the influence of the size of the probe light; i.e., the size of the ring-shaped orbital angular momentum (OAM)-carrying optical vortex (OV), on the RDE. Both the light coaxial and noncoaxial incident conditions were considered in our work. We analyzed the mechanism of the influence on the RDE under the light coaxial, lateral misalignment, and oblique incidence conditions based on the small-scatterer model. A proof-of-concept experiment was performed to verify the theoretical predictions. It was shown that both the signal-to-noise ratio and the frequency spectrum width were related to the OV size. The larger the beam size, the stronger the RDE signal observed in the practical detection. Especially in the lateral misalignment condition, the large OV size effectively reduced the signal spreading and enhanced the signal strength. These findings may be useful for practical application of the optical RDE in remote sensing and metrology.

Tunable acoustic vortex generation by a compact rotating disk

“…Moreover, the working frequency corresponding to different topological charge orders can be simultaneously analyzed for the detected target rotation speed, enhancing the robustness of rotation speed detection. This non-contact detection method eliminates the need for introducing additional incident AV, avoiding the impact of traditional methods on detection accuracy due to the slight misalignment 22 of the incident vortex acoustic beam, the rotating object, and their relative radius size 50 . At the same time, there are challenges requiring further improvement and resolution.…”

“…Contactless detection of rotational information is performed by directing incident AV onto a rotating object and analyzing the rotational Doppler shift of the scattered vortex waves 49 . However, the introduction of additional AV waves inevitably raises concerns about the relative size 50 of the incident vortex acoustic beam, the rotating object, and their slight misalignment 22,51 , which collectively impact detection accuracy.…”

Vectorial Doppler complex spectrum and its application to the rotational detection

“…Since the spectrum for the scattered light by the rough surface is complex, the analyses for the spectrum are significant for the measurement, and it is usually made using a method of the expansion of the different OAM components corresponding to different values of TC. [15][16][17][18][19] All those above are based on scalar vortex beams in which the spatial polarization has a fixed distribution, so the magnitude of the rotating velocity can be, but the direction of the rotation cannot be determined in those cases. A recent attractive study 20,21) using the cylindrical vectorial polarization fields (CVPFs) [23][24][25][26] presented the simultaneous measurement of the magnitude and direction of the velocity of a rotating particle.…”