Photoacoustic and Photothermal Spectroscopy: Principles and Applications introduces the basic principles, instrumentation and major developments in the many applications of Photoacoustic and Photothermal Spectroscopy over the last three decades. The book explains the processes of sound generation by periodic optical excitation and ultrasonic generation by pulsed laser excitation and describes the workings of photoacoustic cells equipped with microphones and piezoelectric transducers. Photoacoustic imaging (PAI) is one of the fastest-growing imaging modalities of recent times. It combines the advantages of ultrasound and optical imaging techniques. These non-invasive and non-destructive techniques offer many benefits to users by enabling spectroscopy of opaque and inhomogeneous materials, (solid, liquid, powder, gel, gases) without any sample preparation, and more.