Tracking the rotation of a birefringent crystal from speckle shift measurement

TL;DR

This paper demonstrates that the rotation of a birefringent crystal can be precisely tracked by measuring the angular shift in speckle patterns caused by the crystal's birefringence, independent of the incident beam's topological charge.

Contribution

It introduces a novel speckle-based method for accurately determining the rotation of birefringent crystals, independent of the incident beam's topological properties.

Findings

Speckle patterns shift with crystal rotation.

E-ray and o-ray speckles have different shift rates.

The method achieves high accuracy in tracking crystal rotation.

Abstract

The random intensity distribution observed due to the propagation of a coherent beam of light through a scattering medium is known as a speckle pattern. The interaction of the speckles with a birefringent crystal, here, YVO4 results in the e-ray and o-ray speckles. It is observed that the e-ray and o-ray speckles experience an angular shift with the rotation of the crystal and the shift depends on the rotation angle of the crystal. It is also found that the rate of the shift is different for e-ray and o-ray speckles, and is independent of the topological charge of the beam incident on the scattering medium. The observed rate of shift of the speckle pattern is found to be same as that of the e-ray and o-ray beams. It is experimentally demonstrated that the rotation of a birefringent crystal can be tracked very accurately from the speckle shift measurement.