Nanosecond pulsed deep-red Raman laser operating at 735 and 750 nm

A wavelength-selectable nanosecond pulsed deep-red Raman laser operating at 735 and 750 nm was demonstrated based on an acousto-optically Q-switched intracavity frequency-doubled KGW Raman laser system pumped by the π-polarized Nd:YLF laser at 1321 nm. To compensate for the strong negative thermal lensing induced by the π-polarized fundamental beam, a positive spherical lens was incorporated, significantly extending the resonator's stability region and enhancing the output power. Under the optimal pulse repetition frequency of 4 kHz, the maximum average output powers of 2.1 and 2.8 W were obtained at 735 and 750 nm, with the pulse widths of 5.6 and 6.6 ns, respectively. Moreover, the pulse energies were elevated to 1.2 and 1.6 mJ at a 1 kHz repetition rate, corresponding to the pulse widths of 3.3 and 5.3 ns and the peak powers of up to 377 and 308 kW, respectively. Notably, the wavelengths of 735 and 750 nm align well with the absorption peaks of the fluorescent dyes BTPETTQ nanoparticles and Sulfo-Cyanine7, respectively, suggesting strong potential for biomedical photoacoustic imaging applications.