Photoacoustic Spectroscopy for Crystal Characterization

Photoacoustic spectroscopy (PAS) is a nondestructive powerful analytical technique based on the photoacoustic effect, discovered by Alexander Graham Bell in 1880. Initially investigated during Bell’s experiments on wireless communication using light, the effect occurs when modulated light irradiates a material, producing sound through thermal expansion. This phenomenon was found to be consistent across solids, liquids, and gases, allowing the creation of spectra that closely resemble traditional optical absorption spectra. PAS operates by dispersing light and recording sound intensity at various wavelengths to obtain valuable material properties. The setup generally includes a PA cell, sample, a modulated light, and a detection system, generally microphone, to capture the acoustic signal resulting from the pressure waves created. In modern applications, PAS has become an essential tool for analyzing optical and thermal characteristics of materials, crystals, semiconductors and biological tissues. The method offers several advantages, including its ability to provide detailed information about different media and detect non-visible spectral regions like infrared and ultraviolet. However, there are also limitations, which, along with its broad applications, will be discussed in this chapter.