Fig. 5. Applications of the rotational Doppler effect (RDE) metrology.

RDE metrology with vortex beams exhibits exceptional adaptability across various conditions, ranging from ideal to complex scenarios such as micro-object rotation detection, tiny rotations, oblique incidence, and lateral misalignment. Utilizing vortex beams with opposite-sign OAM in both reference and measurement paths, this approach accurately identifies micro displacements, the direction of micro-object rotation, and minute velocity changes. The central frequency remains stable despite variations in incident angle and lateral displacement, while the rotational Doppler signal broadens, ensuring extraction of rotational velocity even in cases of oblique incidence and lateral misalignment. References given in the insets