“…Optoacoustic effects originate from the fact that the optical properties of a medium can change as a result of density variations, 62 which can trigger the generation of acoustic waves. [70][71][72][73][74][75][76] When radiation is strongly absorbed, as in the case of Terahertz spectroscopy on liquid water, 59,60 thermoacoustic effects dominate. In first approximation, the absorption triggers thermal expansion that, in turn, can induce a pressure wave with associated mass displacement and density perturbations.…”