Problem of Mode Deformation in Optical Masers

Abstract

Fox and Li first calculated mode shapes in Fabry‐Perot‐type oscillators assuming a passive homogeneous medium between the mirrors. In laser oscillators the gain is strongly depressed by saturation in regions where the amplitude of the mode is large, thus giving a nonuniform gain distribution in the cavity. In addition, nonuniformities in the excitation may lead to gain variations. Through numerical solutions it is found that even with nonuniform gain distribution in the transverse direction, the lower order optical modes as originally calculated represent the electromagnetic fields in the cavity rather accurately. The present work justifies earlier calculations of the number of oscillating off‐axis modes in lasers.