Computer modelling and numerical simulation of the solid state diode pumped Nd:YAG laser with intracavity saturable absorber

Stimulated emission in the Nd:YAG laser with a saturable absorber Cr:YAG is modelled as a superposition of interacting optical modes which are stable in a given optical cavity. The interaction of the active laser crystal and a passive Q-switch with diode pump and optical cavity modes is modelled with account of transversal two-dimentional variation of the pump field and of all participating optical modes. Each elementary volume of an active laser crystal and the Q-switching crystal interacts with all modes (this way modes are nonlinearly linked to each other), and every optical mode interacts with the whole laser crystal. This interaction is given by rate equations. Total number in this set of equations is given by the following formula Ne=2 * kmax * jmax^2 where kmax is number of cavity modes and jmax^2 is the total number of elementary volumes representing intracavity crystals. Most of simulation experiments presented in this paper were done with Ne=2*10^5 (kmax=20 , jmax^2 =10000). Special numerical tools were used to accelerate calculations without loss of precision. Simulation experiments for two laser devices provide quantitative validation of some experimentally observed effects (domination of the fundamental mode in a Q-swithed regime, multimode operation without Q switch) and predict performance of a laser with long pump pulses (trains of laser Q-switched pulses with pule-to-pulse mode switching)