Ho:Tm:YLF laser amplifiers

A series of models is developed that describes a Ho:Tm laser, and predictions from these models are compared with experimental measurements for a variety of Ho:Tm:YLF amplifiers. Modeling is complicated by the plethora of required parameters needed to describe the dynamics of the Ho:Tm laser system versus the paucity of measured parameters. To remedy this, calculations presented here begin with measured energy levels and a quantum-mechanical model to determine a set of crystal-field parameters that are then used to calculate the energy-transfer parameters. Energy-transfer parameters, which describe the dynamics of energy exchange in the Ho:Tm system, are subsequently used in a rate-equation model to describe the dynamics of the lowest four manifolds of both Ho and Tm. Next, predictions of the rate-equation model are used in an amplifier model, which, among other effects, includes the variation of the pump energy density with the position of the probe beam in the amplifier. Results of the amplifier model are then compared with small-signal gain measurements from a variety of Ho:Tm:YLF laser amplifiers. Finally, the models are used to investigate the ultimate performance of a Ho:Tm:YLF laser amplifier by varying the concentrations of Ho and Tm in addition to the length of the end-pumped device. (C) 1996 Optical Society of America.