Influence of Doping Atoms on Nonlinear Absorption, Ultrafast Dynamics and SHG Behaviors in GaSe

In this study, undoped GaSe, 0.1%Er and 0.1%Ce doped GaSe crystals were grown by using vertical Bridgman-Stockbarger technique. The nonlinear absorption properties and ultrafast charge transfer dynamics of all grown crystals were investigated by using open aperture Z-scan and ultrafast pump-probe spectroscopy techniques. The studied crystals showed nonlinear absorption at 1200nm wavelength with 100fs pulse duration. Nonlinear absorption coefficients increase with 0.1%Er and 0.1%Ce doping atoms. This behavior also leads to increasing of the free carrier densities with doping atoms and occurring of the excited states absorption. Second harmonic generation signals of the crystals were measured by fiber optic spectrometer. Second harmonic generation signals of the doped GaSe crystals shifted blue region of the spectrum as compared to the undoped GaSe crystal. According to ultrafast pump-probe experimental results, the undoped GaSe crystal indicates continuous excited state absorption signal while the doped GaSe crystals indicate saturable absorption behaviors after 2ns time delay between 630nm-650nm region corresponding to bottom of the conduction band. The saturable absorption signals indicate that the defect states which are occurred with doping atoms in crystal are localized under the conduction band. In conclusion of the experimental results, nonlinear absorption properties, frequency conversion and ultrafast charge transfer dynamics of the crystals can be controlled by doping atoms in crystals.