Generation of wavelength- and orbital angular momentum-tunable extreme-ultraviolet vortex beams using a spiral phase mirror

Abstract

To generate or manipulate the orbital angular momentum (OAM) of light, various optical elements, such as spiral phase plates, spatial light modulators, diffractive optical elements, and spiral phase mirrors (SPMs) have been used. In contrast to other optical components, the SPM depends only on the angle of incidence, which allows for the manipulation of the OAM values by simply rotating a single SPM or changing the angle of incidence of light. This study theoretically demonstrated the generation of high-quality vortex beams in the X-ray region (within a range of several tens of nanometers) beyond the existing visible and infrared regions using a SPM. Based on the geometry of grazing incidence, by rotating a single SPM, we obtained wavelength-tunable vortex beams with an identical OAM value of l = 1 in the 20–40 nm wavelength range and OAM-tunable vortex beams with various OAM values ranging from l = 3 to l = 5 at a 10 nm wavelength. Based on these characteristics, the tuning range of an SPM was discussed and the variation in the major radius of the elliptical beam formed on the SPM by grazing incidence was analyzed to realize SPM manufacturing. This novel optical technique holds great promise for enabling light-matter interactions at the nanometer scale, such as in the molecular or atomic regions, by implementing easily controllable wavelength- and OAM-tunable vortex beams based on a single SPM.