Reconstruction of specimen thickness from angle-resolved laser transmittance using the transfer matrix method and a genetic algorithm

Abstract

Accurate thickness estimation of transparent and partially absorptive specimens is essential for the optical characterization and quality control of dielectric materials. This paper proposes an inverse estimation framework that combines angle-dependent continuous-wave laser transmittance measurements with the transfer matrix method (TMM) and a genetic algorithm (GA). The TMM model incorporates both s- and p-polarized components under oblique incidence, accounting for the phase thickness variation and interference effects within a single-layer air–specimen–air structure. Experimentally measured transmittance data at multiple incidence angles (1°–5°) for quartz and acrylic samples were used to validate the approach. The GA performs a global search for the optimal thickness, while a local fminbnd refinement ensures convergence to the physical minimum. The results demonstrate strong agreement between the measured and modeled transmittance, confirming that the proposed TMM and GA scheme effectively reproduces interference-induced oscillations and retrieves the specimen thickness with strong agreement relative to the nominal manufacturer specifications. This methodology provides a nondestructive and physics-based solution for layer characterization in transparent and weakly absorbing materials.