Stimulated emission kinetics of neodymium powder lasers

An experimental investigation was made of the time dependence of stimulated emission from Nd³⁺-activated Na₅La(MoO₄)₄, La₂O₂S, and La₃NbO₇ powders pumped by a pulsed tunable rhodamine 6G laser. A single lasing pulse of 1–3 ns duration was observed near the threshold and, as the pumping increased, the number of pulses increased to three or four. At a constant pump power the number of pulses, their duration, and the interval between them were governed by the properties of the materials. Experimental estimates showed that the lasing spectrum of Nd³⁺ in Na₅La(MoO₄)₄ was narrower than 1 cm ^– 1. Comparing the luminescence excitation spectra for the ⁴F_3/2–⁴I_9/2 transition, obtained by pumping below and above the threshold, it was found that most of the excited neodymium ions participated in the lasing in that part of the sample where the pumping exceeded the threshold. A model was used to describe the time dependence of the lasing on the basis of rate equations for a set of weakly coupled active resonators. A comparison of the modeling and experimental results yielded estimates of the Q factors of the effective resonators and of the parameters of the coupling between them.