Generating XUV Vortex Beams with Tunable Orbital Angular Momentum

A beam of XUV radiation is produced when an ultrahigh intensity laser is incident onto an overdense plasma with a sharp density gradient. When this process is driven by a laser that possesses orbital angular momentum (OAM), the resultant XUV light must also have OAM due to conservation of energy and angular momentum. A driving laser with arbitrary OAM 0 ≤ l_L ≤ 1 can be produced by combining a Gaussian beam (l = 0) and a vortex beam (l = 1) with different intensities. In this work, we investigate the properties of the XUV radiation produced by this laser towards the goal of generating high intensity XUV pulses with tunable OAM. We performed 3D particle-in-cell simulations to demonstrate that varying l_L also changes the amount of OAM in the XUV beam. We have found that the OAM of the nth harmonic is not l_n = n l_L as predicted by conservation laws but is instead proportional to l_L^0.7. Lastly, we also propose an experimental configuration to test these predictions.