Fig. 4.

Investigations of the mechanism of thermal-based nonlinearity. (A)Water expansion coefficient $\beta$ as a function of temperature [30](B) The PA signal vs. the optical fluence of gold nanosphere at approximately 4 °C [30]. (C) PA–F curves for both colloidal suspension of gold nanoparticles and diluted India ink [32]. (D) Experimental results of GNP diameter effect on thermal-based nonlinearity at room temperature [31]. Figures reproduced with publisher’s permission [[30], [31], [32]].