High-Harmonic Generation and Optical Torque Interaction via Relativistic Diffraction of a Spatiotemporal Vortex Light

Diffraction of a relativistically-strong light can produce high-order harmonics via the relativistic oscillating window mechanism. In this process, the characteristics of the 2D electron dynamics at the diffraction screen can be imprinted to the generated harmonics, which provides abundant opportunities for manipulating light-matter interaction. In this work, we study single-slit diffraction of a high-intensity spatiotemporal optical vortex (STOV) - a beam carrying transverse orbital angular momentum (OAM). We demonstrate that due to the spatiotemporal structure of the driver, it induces differential electron oscillations on the screen, which conveys the transverse OAM to the high-order harmonic STOV beams. As a result, the topological charges of the harmonic beams are $l = nl_0$, where $l_0$ is the topological charge of the fundamental driving light, and $n$ is the harmonic order. In addition, we show that by controlling the slit angle with respect to the driver' s transverse OAM, the STOV light can exert a torque on the plasma, thus providing a way to manipulate the transverse OAM orientation of the generated harmonics.