A two-mode disk laser with a sub-gigahertz difference frequency based on a degenerate resonator

Two-frequency lasing is obtained in a disk laser with a two-mirror degenerate laser resonator with an M-shaped configuration of an intracavity off-axis beam path. Lasing is implemented on two transverse modes of the lowest order. Two-frequency lasing is obtained due to the inherent spectral-selective properties of the degenerate resonator without the use of additional optical elements. The intermode beat frequency is 360 MHz, and the width of each of the spectral components does not exceed 1.5 kHz (≤5×10^-8 cm^-1).