Vortex phase deterioration common-path interferometry

Abstract

Common-path interferometers (CPIs) are significant due to their compactness and vibration resistance. The usual challenge with CPIs arises due to a very small separation between reference and sample beams, where sending a reference beam through a sample is considered to be a limitation. However, this limitation also makes it difficult to probe the interaction of beams with materials as a function of their phase structure. This study paves the way for a new kind of interferometry that can provide unique phase signatures to study the sample. This paper proposes and demonstrates a novel approach based on thermo-optic refraction, to send both beams through the sample and probe the phase deterioration due to the relative interaction of beams in the material medium. Here, thermo-optic refraction interferometry allows the superposition of a higher-order vortex beam with a non-vortex beam through the phenomenon of thermal lensing. The non-vortex beam is made to expand in a controlled fashion by another laser. The relative interaction between the expanding non-vortex beam and the vortex beam within the sample, results in the output interferogram. The phase deterioration analysis of the output interferogram elucidates medium-driven phase changes. This technique is demonstrated using milk samples by recording the root-mean-square azimuthal phase deterioration of the orbital angular momentum beam.