Saturable absorption during high-intensity laser heating of liquids

The interaction of high-intensity, short-pulse laser radiation with liquids is fundamental to many contemporary technologies. At low laser intensities, the classical model of absorption and heating applies, which assumes a constant absorption coefficient and no dependence on intensity. As the intensity increases, however, a significant fraction of molecules are promoted excited states, whose absorption properties differ from those of the ground state, thus the absorption of the bulk liquid is altered. This phenomenon, called saturable absorption, results in intensity-dependent absorption, heating, and temperature distributions that can deviate significantly from the classical model. This work investigates the thermal aspects of saturable absorption during laser heating of liquids for engineering applications. A microscopically based theoretical model of the radiation absorption and heating processes is presented. Model solutions are discussed and compared with experiment for a contemporary saturable absorbing liquid. Simple engineering criteria and relevant applications are then discussed.