More precise determination of thermal lens focal length for end-pumped solid-state lasers

A method of more precise determination of the focal length of equivalent thermal lens (TL) is presented in this paper. The method is based on the diffraction theory of aberrations. By numerically calculating the optical path difference (OPD) distribution and the Strehl ratio, the focal lengths for “top-hat” pumping and Gaussian pumping are obtained and the equations for the focal lengths are presented by curve fitting. Also the equations for average pump radii are presented. The experiment on a fiber-coupled LD pumped Nd:YAG laser is carried out. The experimental results verify the validity of the method.