Optical Bistability Characteristics In TM³⁺ Ion Doped Laser Crystals

Optical bistability induced by new physical mechanisms in novel materials has become an important research subject of nonlinear optical field. Optical bistability in rare-earth doped crystals not only exploits new nonlinear optical phenomena resulting from the interaction of light with active ions in solid-state mediums, but also has potential applications for all-solid-state wavelength routers and optical switches, as well as bistable optical displays in visible-infrared spectra.In this thesis, we investigated the laser optical bistability in Tm3+,Ho3+ codoped lithium yttrium fluoride crystal, the intrinsic optical bistability in Tm3+ single-doped and Tm3+,Yb3+ codoped laser crystals. The particular physical mechanisms of laser optical bistability and intrinsic optical bistability were analyzed theoretically. The main objective of this work is to extend active optical bistability to a new type of trivalent rare-earth Tm3+ doped laser crystal mediums.We experimently achieved all-solid-state bistable laser output operated at 2μm infrared band in a 792 nm pumped Tm3+,Ho3+ codoped lithium yttrium fluoride (Tm3+,Ho3+:YLF) crystal. We developed a rate equation model of the optical bistability laser in the end-pumped Tm3+,Ho3+ codoped laser crystal, and derived the optical bitability equation of 2μm laser oscillation. The bistable output characteristics of 2μm laser were explained theoretically. Based on the experimental and theoretical analysis, we discussed the physical origin of laser optical bistability generated in Tm3+,Ho3+:YLF laser crystal.We established the coupled rate equation model and the fluorescence emission model of Tm3+ single-doped laser crystal. The numerical simulations showed that intrinsic optical bistability (IOB) and luminescence switching characteristics in visible-infrared spectra can be achievable in Tm3+ single-doped laser crystals pumped by 648 nm laser. We numerically studied IOB hysteresis response of level populations in Tm3+ single-doped laser crystal, bistable emission spetra and luminescence bistability from Tm3+ ions, as well as the chromatic switching from infrared to visible spectra. Meanwhile, we discussed the influences of system parameters on IOB and the physical origin of chromatic switching phenomenon of Tm3+ emission spectra.We numeircally studied the static and dynamic characterisitics of IOB in Tm3+,Yb3+ codoped laser crystal based on the rate equation model of photon avalanche. We discussed the optimization of Tm3+,Yb3+ doped concentrations, the selection of host crystals and the effect of sample temperature. Thereby we proposed the optimal scheme of parameters to achieve IOB in Tm3+,Yb3+ codoped laser crystal and the controllable operation of optical bistability loops. Meanwhile, the transient kinetic responses of IOB switching were numerically studied and the critical slowing down phenomenon of IOB switching in Tm3+,Yb3+ codoped laser crystal was revealed.We presented a general simplified physical model to analyze the IOB problem in Tm3+ single-doped and Tm3+,Yb3+ codoped laser crystals. We obtained the IOB equations, the bistable switching threshold formulas and the necessary conditions of IOB hysteresis in Tm3+ doped laser crystals. The analytic treatment of the simplified model permits us to present a complete analytical interpretation for the IOB phenomena in Tm3+ doped laser crystals. The particular mechanisms and the conditions for IOB to occur in Tm3+ single-doped and Tm3+,Yb3+ codoped laser crystals were discussed and the critical slowing down of IOB switching in Tm3+,Yb3+ codoped laser crystal were interpreted analytically.