Study on atoms and molecules using optical vortex in the extreme ultraviolet region

'Optical vortex,' which is electromagnetic wave with a spiral wavefront, is also called the light carrying orbital angular momentum. Conventionally, various studies have been carried out in the visible to near-infrared wavelength region, taking advantage of the orbital angular momentum owned by the optical vortex and the peculiar intensity distribution of the doughnut shape. In addition, with the recent rapid development of optical vortex generation technology in the shortwave region, interest in optical vortex is increasing in the field of atomic and molecular physics. This paper briefly explains the optical vortex, and introduces the optical vortex generation in the ultrashort ultraviolet region using a helical undulator and its application to atomic and molecular experiments, with a focus on the studies that the authors have been promoting. (A.O.)