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Intrinsic optical bistability in Tm-doped laser crystal pumped at 648nm avalanche wavelength

Intrinsic optical bistability and dynamic hysteresis phenomenon, induced by nonlinear excitation and energy level coupling, are predicted theoretically in single Tm-doped laser crystal pumped at 648nm avalanche wavelength. Taking into account the dominant energy transfer processes including excited state absorption, cross relaxation, energy transfer up-conversion and decay of the metastable level Tm3+ 3F4, the analytical formula of avalanche threshold condition are deduced in the steady-state approximation. Based on the theory of microscopic coupled rate equations, intrinsic optical bistability and influence of system parameters on hysteresis loop are studied numerically in detail by using a four-order Runge-Kutta technique. The numerical results predict that intrinsic optical bistability of near 2 micrometer fluorescence emission relevant to Tm 3F4→3H6 transition is achievable experimentally in single Tm-doped laser crystal. For realization of low threshold optical bistability and notable bistable hysteresis loop, it is beneficial to properly increase Tm3+-doped concentration and suppress energy transfer up-conversion. Furthermore, the interesting results obtained numerically show that laser-induced thermal effect is not the indispensable factor for occurrences of intrinsic optical bistability in rear-earth-doped crystal. Cooperation of nonliear excitation and energy level coupling can essentially lead to intrinsic optical bistability in rear-earth-doped system.