Optical quality in high precision laser cutting

High power laser systems usually generate multimode laser beams. Conventional optics produces noncircular spots for such beams. The presence of a Brewster window or of any other rectangular asymmetries in the mirror coatings or the laser gain medium or structural alignment of the laser cavity would generate rectangular beams whose mode structure is expressed in terms of rectangularly symmetric Hermite-Gaussian modes. This also leads to the formation of noncircular spots. Rectangular beams may be preferable to circular beams because the diffraction-limited divergence angle of rectangular beams is smaller than the divergence of circular beams. Since noncircular spots are azimuthally asymmetric, the heating characteristics of such spots depend on the laser beam scanning direction relative to the characteristic axes of the spot. The heating effect of laser beam scanning direction is investigated in this paper and the temperature field is shown asymmetric about the scanning direction. This effect is important for high precision cutting applications such as integrated circuit cutting.