The role of gas nanobubbles in nonlinear hyper Raman scattering of light in water

In this work, we studied stimulated hyper-Raman scattering in the spectral range near the second optical harmonic of a laser pump in water samples containing gas nanobubbles (bubstons). The spectrum of the hyper-Raman scattering from nanobubble-free water samples was found to differ from that of nanobubbles containing water samples. To interpret these results, we put forward a hypothesis that the detected effect is related to the huge enhancement caused by the generation of a resonance surface plasmon inside a gas nanobubble during optical (laser-induced) breakdown. The plasmon bandwidth Δω was theoretically estimated. It turned out that Δω≈ω0, where ω0 is the resonant plasmon frequency, i.e., in our case, the quality factor of the plasmon oscillator is very low. The estimate of the enhancement factor, which was made based on experimental data, gives ≈1.5×1015.