Yi Longqing
Department of Physics, Chalmers University of Technology, 41296 Gothenburg, Sweden.
Phys Rev Lett. 2021 Apr 2;126(13):134801. doi: 10.1103/PhysRevLett.126.134801.
When a high power laser beam irradiates a small aperture on a solid foil target, the strong laser field drives surface plasma oscillation at the periphery of this aperture, which acts as a "relativistic oscillating window." The diffracted light that travels though such an aperture contains high-harmonics of the fundamental laser frequency. When the driving laser beam is circularly polarized, the high-harmonic generation (HHG) process facilitates a conversion of the spin angular momentum of the fundamental light into the intrinsic orbital angular momentum of the harmonics. By means of theoretical modeling and fully 3D particle-in-cell simulations, it is shown the harmonic beams of order n are optical vortices with topological charge |l|=n-1, and a power-law spectrum I_{n}∝n^{-3.5} is produced for sufficiently intense laser beams, where I_{n} is the intensity of the nth harmonic. This work opens up a new realm of possibilities for producing intense extreme ultraviolet vortices, and diffraction-based HHG studies at relativistic intensities.
当高功率激光束照射固体箔靶上的小孔径时，强激光场驱动该孔径周边的表面等离子体振荡，其充当“相对论振荡窗口”。穿过这种孔径传播的衍射光包含基频激光的高次谐波。当驱动激光束为圆偏振时，高次谐波产生（HHG）过程有助于将基波光的自旋角动量转换为谐波的固有轨道角动量。通过理论建模和全三维粒子模拟表明，n 阶谐波光束是拓扑电荷|l| = n - 1 的光学涡旋，对于足够强的激光束会产生幂律谱(I_{n}∝n^{-3.5})，其中(I_{n})是第 n 次谐波的强度。这项工作为产生强极紫外涡旋以及相对论强度下基于衍射的高次谐波产生研究开辟了新的可能性领域。
