Influence of laser damage on the nonlinear optical properties of core/shell Au/SiO$_{2}$ nanorods

The mechanisms of nonlinear optical response from ensembles of gold nanorods coated with a silicon dioxide (Au/SiO$_{2}$ NRs) shell are analyzed. The $Z$-scan method under the action of 10 ns pulses of the second harmonic of a YAG: Nd$^{3+}$ laser (532 nm) was used to find dependences characteristic of nonlinear absorption and a negative dynamic lens. It is shown that the bleaching of the colloidal solution, which intensifies with increasing pulse energy, is caused by laser destruction of the Au/SiO$_{2}$ NRs, which occurs due to melting, which is confirmed by theoretical estimates. Negative nonlinear refraction is attributed to the response from spherical nanoparticles (Au NPs) formed upon laser destruction of NRs.