Realization of thermally-near-unstable resonator thin-disk laser and compensation of air wedge effect

This paper reports on a Yb: YAG thin-disk laser based on a thermally-near-unstable resonator. The cavity length of the resonator is 3 m, which is 3.5 m less than the cavity length of a stable resonator, simplifying the oscillator structure and reducing the optical loss of the resonator cavity. The disk laser based on a thermally-near-unstable resonator achieves a laser output power of 38.3 W with beam quality approaching the diffraction limit. The laser center wavelength is 1.03 mu m. The resonator becomes misaligned during the increase in pump power due to air convection, reducing laser output power. In this paper, one end mirror of the thermally-near-unstable resonator is replaced with a retro-reflector to compensate for the misalignment of the resonator. The laser output power of the resonator with retro-reflector increased to 81 W. The beam quality M2 factors in the x and y directions are 1.03 and 1.14, respectively. retro-reflector significantly improves the operational stability of the laser.