Fig. 5.

(a) Schematic representation of the events leading from light absorption to photoacoustic signal generation in a PNP aqueous dispersion. (b) Time course and microscopic interpretation of the above events. τ _{therm, gold} and τ _{stress, gold} are fast time constants on the photoacoustic signal time scale when the excitation pulse is of the order of ns. The same is true of τ _{heat diffusion} for most nanoparticles. Thermoelastic expansion of water is the main determinant for signal generation. Adapted with permission from Ref. [60]. Copyright 2016 American Chemical Society.