Alpha-phase indium selenide saturable absorber for a femtosecond all-solid-state laser

We successfully fabricated the high-quality few-layered α-In₂Se₃ and investigated its carrier dynamics and nonlinear optical absorption properties by pump-probe and open-aperture Z-scan technologies. Intra- and inter-band relaxation times were determined to be 7.2 ps and 270 ps, respectively, and the effective nonlinear absorption coefficient was measured as β_eff=-3.9×10³  cm/GW (1064 nm). Based on α-In₂Se₃ saturable absorber, a continuous-wave mode-locking operation was realized. Pulse duration, repetition rate, and maximum output power were measured to be 352 fs, 42.4 MHz, and 0.56 W, corresponding to pulse energy of 13.2 nJ and peak power of 37.5 kW. To the best of our knowledge, this is the first demonstration of non-transition metal chalcogenides applied in ultrafast all-solid-state bulk lasers. This work well verified that α-In₂Se₃ should be a promising optical modulator candidate for all-solid-state lasers.