ABSTRACT
Photoacoustics has a relatively long history dating back to the 1880s, when Alexander Graham Bell first discovered the photoacoustic [PA] effect via observing the generation of sound by absorbing modulated sunlight [1], Since then, relatively little technological development or scientific research took place in PA application before the invention of laser in the 1960s. Benefiting from the directionality, high peak power and spectral purity of laser, numerous PA applications in industrial and sensing fields began to emerge in the 1970s and 1980s [2], In the early stage of photoacoustics, applications were mostly based on the indirect gas-phase detection of signal of solids based on a PA cell, where the acoustic waves generated by laser-induced surface heating propagate in the gas-filled PA cell and then are detected with a microphone. General classes of applications of gas-phase PA technique include PA spectroscopy, PA monitoring of deexcitation process, PA probing of thermoelastic and other physical properties of materials, and PA generation of mechanical motions [3].
