Heating in a CW Nd-pentaphosphate laser

In a Kr-laser pumped CW Nd-pentaphosphate (NdP
5
O
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) laser, with a threshold of 1.6 mW, an internal quantum efficiency of 63 percent is measured using a novel method. Bistable operation between oscillating and nonoscillating regimes is observed, resulting from the thermal lens created in the pumped zone. If stimulated emission is initially absent, this lensing effect is strong, making the resonator unstable and stimulated emission cannot build up. With stimulated emission initially present, heat development is reduced by the stimulated process itself and the resonator remains in the stable regime. For both situations, temperatures in the pumped area are determined using Raman spectroscopy. For the nonlasing situation, a fluorescence quenching rate of 68 percent, originating from Nd-Nd interactions is deduced, in close agreement with an earlier finding.