Stimulated scattering effects in gold-nanorod-water samples pumped by 532 nm laser pulses

Stimulated scattering in gold-nanorod-water samples has been investigated experimentally. The scattering centers are impurity particles rather than the atoms or molecules of conventional homogeneous scattering media. The pump source for exciting stimulated scattering is a pulsed and narrow linewidth second-harmonic Nd: YAG laser, with 532 nm wavelength, ~8 ns pulse duration, and 10 Hz repetition rate. Experimental results indicate that SMBS, SBS and STRS can be generated in gold-nanorod-water samples under appropriate pump and absorption conditions. The incident pump energy has to be larger than a certain threshold value before stimulated scattering can be detected. The absorption coefficient of samples at 532 nm wavelength depends on the one of characteristic absorption bands of gold nanorods located around 530 nm. A critical absorption coefficient can be determined for the transition from SBS to STRS. Also, the spectral-line-broadening effects of STRS have been observed, the line-shape presents a pseudo-Voigt profile due to the random thermal motion of molecules and strong particle collision.