Digital holographic imaging of thermal signatures and its use in inhomogeneity identification. (January 2023)

• Record Type: Journal Article
• Authors: Utadiya, Subhash; Trivedi, Vismay; Sheoran, Gyanendra; Srivastava, Atul; Claus, Daniel; Cabrera, Humberto; Anand, Arun
• Is Part Of: Optics and lasers in engineering. Volume 160(2023)
• Publication Date: 2023-01
• Subjects: Digital holographic interferometry -- Lens-less Fourier transform digital holography -- Thermal diffusion -- Defect detection -- Scalar diffraction; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2022.107227
• Languages: English
• ISSNs: 0143-8166

Abstract

Highlights: Demonstration of Lens-less Fourier transform digital holographic system for real time imaging of thermal diffusion process. Determination of thermo-optic coefficients of the investigated mediums. Quantification of thermal signatures in transparent phase mediums for detection of regions with different thermos-optic constants (inhomogeneity identification). Sub-surface inhomogeneity identification by thermal stressing. Abstract: Thermal diffusion results in spatiotemporally evolving temperature distribution in material mediums. In dielectric mediums it will also lead to change in local refractive index. Digital holographic interferometry can be used for high contrast quantitative phase imaging of spatially and temporally evolving refractive index variations in dielectric mediums, arising due to temperature changes. Phase retrieved from numerically processed digital holograms recorded at different time instances can be compared to obtain this information. Since the thermal conductivity varies for materials, the thermal diffusion and hence the refractive index across them will also vary. Time varying optical path length distributions of the test sample under thermal stress, obtained from the phase maps retrieved from the recorded holograms, can be used to obtain this information. This leads to detection of regions having different thermal conductivities and hence identification of inhomogeneities in the test sample. Lens less Fourier transform digital holographic interferometry is a perfect tool to quantify optical path length distributions with nanometre accuracy to quantify spatiotemporally evolving refractive index distributions. In this technique, a single Fourier transform of the recorded hologram yields the spatial distribution of object phase, making it ideal for real time imaging and applications. Here we describe our efforts in the development lens less Fourier transform digital holographic interferometric technique for the imaging and quantification of spatiotemporally evolving refractive index distributions in test samples under thermal stress and its application in detection of surface and sub-surface inhomogeneities.