Near-infrared excitation profile study of surface-enhanced hyper-Raman scattering and surface-enhanced Raman scattering by means of tunable mode-locked Ti: sapphire laser excitation

Excitation profiles of surface-enhanced hyper-Raman scattering (SEHRS) and surface-enhanced Raman scattering (SERS) of crystal violet on colloidal silver were measured using 1 ps Ti:sapphire laser pulses at wavelengths between 750 and 830 nm. Our measurements allowed the direct determination of the ratio between SEHRS and SERS intensities which exhibited a strong dependence on excitation wavelength. The measured variation of this ratio can be explained by different electromagnetic contributions to the enhancement factors of SEHRS and SERS at different excitation wavelengths. Total surface enhancement factors of hyper-Raman scattering can be estimated to be the order of 1014.