Angular momentum oscillation in spiral-shaped foil plasmas

Two types of spiral-shaped foils are investigated for generating significant angular momentum (AM) in plasmas by reflecting a relativistic Gaussian pulse into a vortex laser beam with the same topological charge. This is the first time to find that AM oscillation exists in specific spiral-shaped foils during laser-plasma interaction, while AM oscillation is not observed in other types of foils. Both three-dimensional particle-in-cell simulations and theoretical results have confirmed this finding. AM oscillation is demonstrated to be induced by the asymmetric field on the foil surface, and this asymmetric field can be modulated in order to strengthen or weaken the oscillation amplitude by redesigning the foil surface. AM oscillation is expected to bring insight into radiation, particle heating and other mechanisms with AM effects.