Direct generation of the lowest-order vortex beam using a spot defect mirror in the ultraviolet region

The creation of ultraviolet optical vortex beams with the topological charge of $ \vert l \vert = 1 $|l|=1 at the wavelength of 325 nm was demonstrated from a He-Cd metal vapor laser with a spot defect mirror. The measured $ {{\rm M}^2} $M2 factor was close to the theoretical value of two of the $ {{\rm LG}_{01}} $LG01 Laguerre-Gaussian mode. Some interference experiments showed that the obtained vortex beams were stable enough for practical applications such as holographic lithography.