Thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer

Luis G Rodriguez; Joseph Niemela; Humberto Cabrera

doi:10.1016/j.heliyon.2023.e20492

Thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer

Heliyon. 2023 Sep 27;9(10):e20492. doi: 10.1016/j.heliyon.2023.e20492. eCollection 2023 Oct.

Authors

Luis G Rodriguez¹, Joseph Niemela², Humberto Cabrera²

Affiliations

¹ Universidad Técnica de Manabí, Facultad de Ciencias Básicas, Departamento de Física, Avenida Urbina, Portoviejo, 130105, Ecuador.
² MLAB, STI Unit, The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy.

Abstract

A thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer for measuring optical absorption and thermal diffusivity coefficients in pure solvents is described in this work. The approach combines the sensitivity of both thermal lensing methods and interferometry techniques. The photothermal effect is induced by a pump laser beam generating localized changes in the refractive index of the sample, which are observed as a shift in phase of the interference pattern. Each interference pattern is recorded by means of a digital camera and stored as digital images as a function of time. The images are then numerically processed to calculate the phase shifting map for a specific time. From each phase shifting map, the experimental phase difference as a function of time is calculated giving a phase-time transient, which is fitted to a mathematical model to estimate the optical absorption and thermal diffusivity of the sample. The experimental results show that the sensitivity is approximately λ/4800 for the minimum phase difference measured.

Keywords: Fourier transform; Interferometry; Photothermal effect; Thermal diffusivity; Thermal lensing.