Optical wavelength dependence of photoacoustic signal of gold nanofluid

The photoacoustic (PA) effect is based on the generation of acoustic waves upon absorption of light [1] . In a nutshell, the mechanism is based on the conversion of the absorbed light into heat, yielding a temperature rise inside the sample. This results in acoustic waves generated by the thermal expansion of the heated medium (a sketch of the effect is reported in Fig. 1a ).