Effects of misalignment in focusing CO2 laser beam by parabolic mirror

Abstract

Focusing characteristics of 90° off-axis parabolic mirror is analyzed on the basis of the geometrical and physical optics to explore the effects of angular misalignment of the optical axis and divergent angle of CO2 laser on the intensity distribution in the focus spot. It was experimentally demonstrated that the focused power density increases in proportion to the square of the incident beam diameter with precise alignment because it is free from the spherical aberration. The angular misalignment decreases the focused power density due to astigmatism. The sensitivity of the misalignment of the parabolic mirror is approximately 20 times as large as that of spherical lens. As the incident beam diameter increases, the angular misalignment decreases more rapidly the focused power density. When the non-parallel laser beam incident to the parabolic mirror, coma is produced to decrease the power density at focal point with movement of focus spot in the focal plane along the optical axis. The effect of the misalignment angle on the penetration depth was also demonstrated in laser welding stainless steel. A simple measurement method is proposed, which can quickly determine the angle of the misalignment by using the beam analyzer with a slit probe.Focusing characteristics of 90° off-axis parabolic mirror is analyzed on the basis of the geometrical and physical optics to explore the effects of angular misalignment of the optical axis and divergent angle of CO2 laser on the intensity distribution in the focus spot. It was experimentally demonstrated that the focused power density increases in proportion to the square of the incident beam diameter with precise alignment because it is free from the spherical aberration. The angular misalignment decreases the focused power density due to astigmatism. The sensitivity of the misalignment of the parabolic mirror is approximately 20 times as large as that of spherical lens. As the incident beam diameter increases, the angular misalignment decreases more rapidly the focused power density. When the non-parallel laser beam incident to the parabolic mirror, coma is produced to decrease the power density at focal point with movement of focus spot in the focal plane along the optical axis. The effect of the misal...