Vortex phase deterioration common-path interferometry

Abstract

Common path interferometers (CPI) are significant due to their compactness and vibration resistance. The usual challenge in CPI would arise due to a very small separation between reference and sample beams, where sending a reference beam through a sample is considered as a limitation. But this limitation also makes it difficult to probe the interaction of beams with material as a function of their phase structure. This study can pave the way for a new kind of interferometry that can provide unique phase signatures to study the sample. The 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 (TORI) 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 of 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 elucidate medium driven phase changes. This technique is demonstrated using the milk samples by recording the RMS azimuthal phase deterioration of the OAM beam.