Breakup of cw multimode oscillations and low-frequency instability in a microchip solid-state laser by high-density pumping

The effect of high-density pumping on lasing mode spectra is investigated in a laser-diode pumped microchip LiNdP₄O₁₂ (LNP) laser. Breakup of multimode oscillations, leading to single-mode oscillations, is observed experimentally. It is shown analytically that the enhanced Auger recombination process among excited Nd ion pairs results in a strong deformation of spatial hole-burning patterns, leading to a destabilization of the multimode laser output via a quadratic-to-quartic transition of the spatial distribution of population inversion. The destabilization threshold is shown to be given by a universal relation which reproduces experimental results quite well. A mode-partition instability is observed above the transition, whose properties are intimately related to the antiphase dynamics.