Nonlinear and saturable absorption characteristics of Ho doped InSe crystals

InSe:Ho (%0.005) and InSe:Ho (%0.05) single crystals were grown using the Bridgman–Stocbarger method. The nonlinear and saturable absorption characteristics of InSe:Ho (%0.005) and InSe:Ho (%0.05) single crystals were investigated by open aperture Z-scan technique with 4 ns and 65 ps pulse durations at 1064 nm. Both crystals show nonlinear absorption for 4 ns pulse duration at low and high input intensities. However, picosecond measurements show saturable absorption behavior at low input intensities while nonlinear absorption becomes dominant at high input intensities. This indicates that the life time of the doping states is shorter than 4 ns pulse duration. Saturable absorption behavior can be attributed to filling of the doping states. Our results show that nonlinear absorption coefficient increases with increasing Ho concentration due to increasing of free carrier concentration.