Deflection of a reflected intense spatiotemporal optical vortex beam

In this Letter, we reveal a new deflection effect in the reflection of an intense spatiotemporal optical vortex (STOV) beam. When a STOV beam with relativistic intensities (>1018 W cm-2) impacts on an overdense plasma target, the reflected beam deviates from the specular reflection direction in the incident plane. Using two-dimensional (2D) particle-in-cell simulations, we demonstrated that the typical deflection angle is of a few milliradians and can be enhanced by using a stronger STOV beam with tightly focused size and higher topological charge. Though similar to the angular Goos-Hänchen effect, however, it is worth emphasizing that the deviation induced by a STOV beam exists, even in normal incidence, revealing an essentially nonlinear effect. This novel effect is explained from the viewpoint of angular momentum conservation, as well as the Maxwell stress tensor. It is shown that an asymmetrical light pressure of the STOV beam breaks the rotational symmetry of the target surface and leads to nonspecular reflection. Unlike the shear press of an Laguerre-Gaussian beam, which only acts in oblique incidence, the deflection caused by the STOV beam exists more widely, including in normal incidence.