<title>High-efficiency laser resonators for high-brightness beam-generation with application to micromaterial processing and nonlinear processes</title>

Abstract

Industrial high precision micro-material processing with solid-state lasers needs the reliable and efficient generation of high brightness laser beams. The key problems for this goal are the control of the thermal effects (lensing) in the active material and the overlap efficiency between the resonator mode and the pumped active material volume. Modern solid state lasers with low thermal effects such as zig-zag slab lasers have non circular geometries difficult to adapt for high efficiency and brightness simultaneously. Resonators comprising a cylindrical telescope, resulting in an elliptical beam section in the active material of rectangular geometry but nevertheless a circularly symmetric output beam can increase the efficiency and beam quality and also compensate for eventual astigmatic effects of the active medium. These lasers yield therefore TEM00 output beams (pulsed, free running) with a beam quality of M<SUP>2</SUP><1.7, pulse powers up to several kW and intensities up to 500MW/cm<SUP>2</SUP> for a spot diameter of 10 to 15micrometers . Such lasers are ideally suited for industrial high precision cutting and drilling, but also for quasi-cw harmonic generation, where the beam quality influences directly the conversion efficiency via the limited angular phase matching acceptance angles. Laser cutting with fundamental mode Nd-YAG lasers at 1.06micrometers and at 532nm (SHG efficiencies up to 17%) yields a minimal kerf width down to 15 micrometers and heat affected zones of less than 2micrometers .