Focusing of high power single mode laser beams

Abstract

Newest developments in diode pumped solid state lasers brought up beam sources with very highly focusability and efficiency. These new high focusable thin disk-and fibre lasers provide beam qualities in the range of M² = 10 down to M² = 1.2 at an output power up to 3 kW.To achieve the appropriate power density distribution for material processing, the laser beam has to be transformed by a system of lenses. Due to imperfections of the involved lenses and intermediate optics, the beam parameter product respectively the M² might be worse than expected. So the focus diameter might be larger as calculated [1], [2], [3].Additionally a laser induced focal shift is caused by the absorption of laser light, which results in rising local temperatures of the involved lenses. The gradient in temperature results in mechanical deformation and a radial gradient of the refraction index. This process is strongly dependent on the power density of the collimated laser beam and the cooling of the optical components.Newest developments in diode pumped solid state lasers brought up beam sources with very highly focusability and efficiency. These new high focusable thin disk-and fibre lasers provide beam qualities in the range of M² = 10 down to M² = 1.2 at an output power up to 3 kW.To achieve the appropriate power density distribution for material processing, the laser beam has to be transformed by a system of lenses. Due to imperfections of the involved lenses and intermediate optics, the beam parameter product respectively the M² might be worse than expected. So the focus diameter might be larger as calculated [1], [2], [3].Additionally a laser induced focal shift is caused by the absorption of laser light, which results in rising local temperatures of the involved lenses. The gradient in temperature results in mechanical deformation and a radial gradient of the refraction index. This process is strongly dependent on the power density of the collimated laser beam and the cooling of the optical components.