Photothermal digital holography for imaging and characterization of multilayered structures

Imaging multilayered hidden structures is challenging due to scattering, diffusion, and varied material responses. We demonstrate photothermal digital holography combining laser-induced heating with phase-sensitive holography for non-invasive imaging and characterization of hidden layers in multilayered samples. A low-power probe and an oblique high-power excitation beam enable simultaneous multilayer imaging. Absorption-induced heating caused refractive index changes in the multilayered structure, leading to phase shifts in the probe beam. Experiments on different materials revealed distinct thermal signatures. Oblique excitation enabled layer discrimination from a single hologram, and fitting spatial phase profiles with a thermal lensing model and temporal phase profiles with an error-function model yielded sample characterization.