Spectral analysis of photoacoustic ultrasound generation in metal-polymer layered structures using a semi-analytical approach

Abstract

This study presents a spectral analysis of photoacoustic ultrasound generation in layered structures comprising metal thin films and polymer layers, applying a semi-analytical approach where general solutions are derived analytically and their arbitrary constants are determined numerically. The investigation focused on elucidating the fundamental mechanisms involved in generating ultrasonic waves through incident laser light, encompassing comprehensive examinations of photoacoustic phenomena such as light absorption, heat generation and diffusion, thermal expansion, and the generation and propagation of elastic/acoustic waves. Subsequently, the study aimed to identify the operating principles underlying the enhancement of ultrasonic wave production through addition of either a metal thin film or a polymer layer. Special emphasis was placed on characterizing optical and acoustic resonances that occur during the photoacoustic conversion process. Finally, the study provided a detailed analysis of the impacts of key parameters, including the wavelength and pulse frequency of the laser light, as well as the materials and dimensions of the metal thin films and polymer layers, on the performance of the photoacoustic ultrasound generator. Insights gained from this spectral analysis significantly enhanced academic understanding of photoacoustic conversion mechanisms in layered photoacoustic generators. Moreover, these insights are expected to offer valuable guidance for optimizing and improving ultrasound generation techniques across various disciplines, including biomedical imaging, non-destructive testing, and materials science.