Surface plasma wave excited by laser pulse oblique incident on a double-layer plasma target and its application

Surface plasma wave (SPW) will significantly affect the subsequent mutual coupling between laser and plasma，so there are many important applications such as particle acceleration driven by laser pulses and transmission enhancement. In this paper, the properties of the SPW produced by an ultra-short and ultra-intensity laser pulse incident on a double-layer plasma target are studied by using the all-electromagnetic large-scale two-dimensional particle in cell (PIC) simulations. It is shown that the high-intensity laser incident with a large angle, θ =75°, can drive the electrons of the low-density layer to form a transportable periodic structure with the propagation speed close to light speed, and excite electrostatic wave whose wavelength is similar to that of the incident laser and is numerically close to the theoretical results according to previous theory. In order to excite SPW, the laser intensity needs to reach a certain threshold. Besides, the ratio of the surface wave intensity to the incident laser intensity in the double-layer target case obviously deviates from the theoretical results of the single-layer target case, showing a nonlinear relationship. In the second part of the simulation, it is found that SPW can significantly enhance the transmission of subsequent laser pulse, allowing the subsequent laser to break through the "black barrier" due to the dense plasma. A pre-laser irradiates the double-layer plasma target at θ = 75°, and then the subsequent laser is normally incident after a delay of Δt = 23T. As a result, an obvious electromagnetic wave with the same direction as the sub-laser can be observed behind the target which indicates that the sub-laser absolutely transmits the dense plasma. In comparison, when a single laser normally incident on the target without pre-laser while other conditions keep unchanged, no obvious wave could be distinguished behind the target, that is, all the field is nearly zero. Another simulation where a single-layer target is injected by pre-laser and sub-laser in order but the wave behind the target is also unobservable proves that it is SPW which plays the main role in transmission enhancement instead of accelerated hot electrons on the target which can also transport the laser energy.