Abstract

An unstable resonator is widely used as a high-power CO₂ laser for material processing. The intensity profile of an annular beam from the unstable resonator varies with the propagation distance due to the diffraction effect. As a result, the intensity profile of the incident beam on a focusing lens is influenced by the distance from the laser to the lens. Since the intensity profile of the focused beam, which has a significant effect on laser welding, depends on that of the incident beam on the lens, it is important to know the propagating and focusing characteristics of the laser beam. However, we know little of such characteristics for an annular beam, because no analytical method has been available. For a stable resonator, the analytical expressions for a Gaussian beam have been derived and found to be useful for actual optical systems.¹

© 1986 Optical Society of America