Competition between stimulated Brillouin and thermal Rayleigh scattering in Au-nanorods/water system

The use of a simple focused optical cell to present the competition between stimulated Brillouin scattering (SBS) and stimulated thermal Rayleigh scattering (STRS) has been investigated experimentally. An Au-nanorod/water sample as the scattering medium pumped by a pulsed narrow-linewidth second-harmonic Nd:YAG laser with ∼532 nm wavelength, ∼8 ns pulse duration, and 10 Hz repetition rate was used. Experimental results indicate that the absorption coefficient of Au-nanorod/water samples is important for the competition between SBS and STRS. When the absorption coefficient $\alpha$ is smaller than a critical value ${\alpha }_{cr},$ SBS will be dominant during the backward stimulated scattering process. By the same token, when the absorption coefficient $\alpha$ is larger than a critical value ${\alpha }_{cr},$ SBS will be greatly suppressed and STRS will be dominant. (paper)