Analysis of a laser resonator from the measurement of thermal aberrations in a laser-diode side-pumped Nd : YAG laser with a wavefront sensor

Abstract

A method to analyze a laser resonator from the measurement of thermal aberrations in a gain medium is described. Thermal wavefront aberrations in a laser-diode side-pumped Nd:YAG laser are measured with a wavefront sensor. The defocus (Z(2)(0)) that is responsible for the thermal lens is the dominant wavefront aberration mode in the Nd:YAG gain medium. A maximum Zernike coefficient of 2.08 mu m was obtained for the defocus at a pump power of 277 W under a non-lasing condition. Higher-order aberrations, such as spherical aberration (Z(4)(0)), coma (Z(3)(1)), and trefoil (Z(3)(3) and Z(3)(-3)), are also observed. The wavefront map of higher-order aberrations shows the distribution of the absorbed pump energy in the gain medium. The maximum root-mean-square (rms) value of the Zernike coefficient for higher-order aberrations is 0.07 mu m. The characteristics of the Nd:YAG laser resonator, such as the resonator stability and the spot size, are analyzed by calculating the thermal focal length from the measured defocus.