Some features of ultrashort pulse generation in a distributed feedback dye laser with two-photon pumping

Tunable generation of ultrashort pulses was achieved using a dynamic distributed-feedback (DFB) rhodamine 6G dye laser under conditions of two-photon optical pumping by single fundamental-frequency pulses from an actively mode-locked YAG:Nd laser. At a dye concentration of 1.6 X 10 ^– 2 mol/liter, the lasing threshold of the DFB laser was reached at a pump energy of ~ 6 mJ which corresponded to an intensity of ~ 7.7 GW/cm² in the active zone. The laser operated stably in the 580–606 nm wavelength range. The width of the emission line was 0.1–0.5 nm. A positive chirp of the lasing frequency was observed due to nonlinear modulation of the active medium refractive index in the high-intensity two-photon pump field.