Experimental determination of fractional thermal loading in an operating diode-pumped Nd : YVO4 minilaser at 1064 nm

A practical in, situ method is described and used for determination of the fractional thermal-loading parameter eta(h) in an operating diode-pumped Nd :YVO4 minilaser at 1064 nm. Readily applicable to the thermal characterizat ion of other solid-state media, the method is based on the fact that therma lly induced lensing will cause the laser oscillation to be quenched at a cr itical pump power whose magnitude depends on the cavity configuration, ther mo-optical properties of the gain medium, and, in particular, on the value of eta(h). In the experiments described here, a 0.5-mm-long coated Nd:YVO4 crystal with 3-at. % Nd concentration was used to construct the diode-pumpe d laser with a flat highly reflecting end mirror and an intracavity lens. F or the method to be effective, the resonator was set up close to the edge o f the stability range. Above the oscillation threshold, the pump power at w hich lasing was quenched because of the onset of the thermally induced reso nator instability was measured as a function of the intracavity lens positi on. A numerical model that accounted for absorption saturation and pump-ind uced thermal lensing was then used to analyze the experimentally measured d ata with eta(h) as an adjustable parameter. The average best-fit value of e ta(h) was determined to be 0.40 with an estimated statistical variation of 8%. (C) 1999 Optical Society of America.