Development of a hyper-Raman microspectroscopic system using a wavelength-tunable laser source

In this study, we developed a hyper-Raman (HR) microscopic system using an optical parametric oscillator (OPO) pumped by a picosecond mode-locked Nd:YVO4 laser source. Owing to the wavelength tunability of OPO, the two-photon electronic resonance effect can be investigated in a broad spectral range of 345-495 nm. As a proof-of-principle experiment, we performed HR imaging of TiO2 single crystals. In addition to HR, second harmonic generation (SHG) and two-photon excitation fluorescence (TPEF) were observed simultaneously depending on the excitation wavelength.