MODELING OF THERMAL LENSING AND HIGHER-ORDER RING MODE OSCILLATION IN END-PUMPED CW ND-YAG LASERS

The influence of thermal lensing and mode matching on the oscillating mode in the end-pumped Nd:YAG laser is investigated. Thermal lensing was measured by probing the output beam divergence of a dynamically stable resonator. The magnitude of lensing expected due to thermal dispersion was confirmed in a distinct range of adequate mode matching. Residual phase front curvature and superimposed higher order ring mode oscillation of the active resonator were found to limit precise quantization. Measurements on arrangements which typically exhibit higher order ring mode oscillation were performed, and compared to a refined model. The refined model is based on a modified numerical calculation of the eigenstate of the electrical field in the active resonator. The active medium is described by a general complex aperture transmission function. This function defines the transverse mode discrimination in the active resonator. Finally, the conditions for fundamental mode oscillation without the use of aperture stops in the active resonator are estimated.