Abstract

The performance of a solid-state laser is strongly influenced by thermally induced distortions (temperature-and strain-induced variation of the refractive index and curvature of the end face). All these effects contribute to the thermal lensing in the rod. To measure the dioptric power, we make use of the cylindrical symmetry of the pump and rod geometry and the optical isotropy of the crystal. During laser operation the stimulated emission reduces the amount of spontaneous emission at the location of the laser mode. With a CCD camera the distribution during laser operation and without laser emission is recorded through a planar facet along the rod axis. Under presumption of cylindrical symmetry the three-dimensional distributions can be reconstructed with a numerical code. By comparing these two distributions we developed a method to directly determine the radius of the fundamental mode in the crystal (Fig. 1). Using the propagation matrix method, the dependence of the mode radius w on the pump power P can be derived [ref 1], w(P) contains a material constant f^*. the specific focal length, which can be found by comparing the calculated mode radius in the crystal with the mode radius determined in the experiment. The measurements were performed with a single end-pumped Nd:YAG rod and f^* was fond to be 4.03 m-W/mm² (Fig 2)

© 1998 IEEE