Double-slit interference of a relativistic vortex laser

The interference of a relativistic vortex laser is investigated for the case when a linearly polarized Laguerre-Gaussian pulse impinges on a double-slit solid target. Three-dimensional particle-in-cell simulation results show that the interference fringes of high-order harmonics are twisted, similar to that of the fundamental vortex laser. The twisting order of the interference pattern is determined by the order of the vortex high-order harmonics, which can be explained by the classic double-slit interference models. The usual double-slit interference has been extended to the regime of relativistic intensity, which may have potential applications for measuring the topological charge of vortex high-order harmonics.