Immation of Excitation Energy in Doped Crystals

P. Le Boulanger, J.-l. Dorralan, S. Girard +1 more

Valery E. Egorushkin, V. E. Panin, E. V. Cavushkin +1 more

Li Li, Xinlu Zhang, Lixue Chen

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.

Massimo V. Fischetti, William G. Vandenberghe

Robert D. Jenkins, Davıd L. Andrews

Summary form only given. The migration of excitation energy within dielectric crystals doped with lanthanide ions is a rich area for the study of mechanisms involving both conventional pairwise resonance energy transfer and more complex many-body effects. Within the framework of molecular quantum electrodynamics, we present a delineation of systems undergoing simultaneous transfer from two pre-excited donor ions to a single ground-state acceptor, termed three-centre energy pooling. Calculations lead to the identification of two competing mechanisms of transfer co-existing in each system-one cooperative pathway where the excitation is transferred directly to the acceptor from both donors, alongside an accretive mechanism where the excitation energy of one donor is accrued by a second, with net transfer to the acceptor ensuing.

Alexander V. Kir’yanov, Nikolai N Il'ichev

A novel method is reported for calculating the nonlinear resonant change in refractive index of a doped saturable medium at the short-pulse excitation. The derived system of equations for energy density and phase of a short pulse propagating in the doped medium allows one to address a rather general case of the resonant index non-linearity caused by the dope's population perturbation (bleaching) effect. As an example, the energy-dependent changes in the refractive index and transmission coefficient of a Cr4+:YAG crystal under the ns-range (wavelength 1.06 μm) excitation are modeled.