Beam quality improvement by means of unstable resonator with variable reflectivity output coupler

Investigations aimed at the production of high power beams with diffractionally limited quality are carrying out in the Institute for Problems in Mechanics since 1992. Up to 5 kW CW output beam characterized by M-2 less than 1.7 was produced with Lantan-5 industrial fast-transverse-flow CO2 laser by means of the unstable resonator with variable reflectivity output coupling mirror (VRM). Both theoretical and experimental investigation of the parameters of the beam produced by VRM unstable resonator are presented. The results of beam quality measurements are in good agreement with theoretical evaluations, and processing performance of the beam corresponds to the measured value of M2.The quality of the output beam in resonators with VRM may be further improved by appropriate choice of the parameters of variable thickness reflective layer.