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Laser-driven high-quality ion beams hold immense potential for applications in diverse fields such as tumor therapy, fast ignition, and so on. However, current experimental ion beams are often constrained by either a large energy spread or relatively low energy. In this paper, we proposed a novel scheme for generating quasi-monoenergetic proton beams by irradiating near-critical-density plasmas, which have a density gradient with a picosecond laser pulse. This approach leverages two key aspects: first, the sustained interaction between the laser pulse and the plasma enhances the duration of magnetic vortex acceleration, thereby promoting extended ion acceleration. Second, the utilization of a multi-species target facilitates the formation of a dual-peaked electric field, which leads to the accumulation of protons in the negative gradient of the accelerating phase, resulting in a quasi-monoenergetic proton beam. The two-dimensional particle-in-cell simulation reveals that by employing a laser intensity of 1.37 × 1020 W/cm2 with a pulse duration of 0.5 ps, we can achieve a carbon ion beam with an energy of 50 MeV/u, and a quasi-monoenergetic proton beam exhibiting a cutoff energy of 160 MeV/u, a peak energy of 75 MeV/u, an energy spread of 3.1 % , and an angle divergence of ∼ 3.2°. Furthermore, the quasi-monoenergetic property is corroborated in three-dimensional simulation results, underscoring the robustness and effectiveness of our proposed scheme. [ABSTRACT FROM AUTHOR]

The mode conversion efficiency (CE) of the relativistic Laguerre–Gaussian (LG) laser is researched in detail within the context of current petawatt laser facilities. The topological charge, radial integer, laser central wavelength, laser bandwidth, and the design of reflective phase plate are integrated into a unified equation in theory. It is found that the vortex laser mode can be expanded as a series of LG modes, with calculations indicating that the LG10 mode predominates, constituting ∼78% of the total mode distribution. Our analysis reveals that mode CE tends toward a saturation value as the number of steps of the reflective phase plate increases. The 32-step phase plate utilized in relativistic systems is fine enough to obtain a higher CE for LG10 mode lasers, which is also verified in three-dimensional particle-in-cell simulations. This research holds promise for optimizing the design of reflective phase plates to enhance the conversion efficiency of intense LG lasers, thereby facilitating broader applications in intense vortex laser technologies. [ABSTRACT FROM AUTHOR]

Electron‐only magnetic reconnection, a novel type of reconnection where only electron dynamics is involved, has recently been observed in turbulent plasmas in the Earth's magnetosphere. In this letter, using particle‐in‐cell simulations, we demonstrate that electron‐only reconnection can be created via laser‐plasma interactions. The reconnection current sheet is carried by electrons, and its width is at the electron inertial scale. Moreover, only electron outflow is observed, while the ion outflow is negligible. The duration of the reconnection is found to be within the electron scale, thus there is no sufficient time for ions to respond. The energy conversion during electron‐only reconnection mainly occurs in the vicinity of the X‐line, and is dominated along the perpendicular direction. By analyzing the Poynting flux patterns, we find that the reconnection electric field dominates the whole energy conversion. This study advances our knowledge of the energy dissipation mechanism in the electron‐only reconnection regime. Plain Language Summary: Magnetic reconnection is a fundamental energy converting process that occurs in space and laboratory plasma. Generally, magnetic reconnection involves both ion dynamics and electron dynamics. Recently, a new type of magnetic reconnection has been discovered in the Earth's turbulent magnetosheath and magnetotail, which is called electron‐only reconnection. In electron‐only reconnection, only electron outflow is observed since there is no time and/or space for ions to couple. In this study, by performing numerical simulations, we create the electron‐only reconnection via laser‐plasma interaction, and investigate the energy conversion during reconnection in detail. We find that both the spatial and temporal scale of the reconnection is within the electron scale. During magnetic reconnection, energy is transferred from the electromagnetic fields to the electrons, mainly occurring near the X‐line. The reconnection electric field plays a crucial role in energy conversion. This study improves our understanding of how energy is converted to electrons in electron‐only reconnection. Key Points: Simulations show that electron‐only magnetic reconnection can be created via laser‐plasma interactionsBoth the spatial and temporal scales of the reconnection are at the electron scale, and only electron outflow is observedEnergy conversion mainly occurs in the vicinity of the X‐line, and is driven by the reconnection electric field [ABSTRACT FROM AUTHOR]

With the development of ultra-intense laser technology, the manipulation of relativistic laser pulses has become progressively challenging due to the limitations of damage thresholds for traditional optical devices. In recent years, the generation and manipulation of ultra-intense vortex laser pulses by plasma has attracted a great deal of attention. Here, we propose a new scheme to produce a relativistic vortex laser. This is achieved by using a relativistic Gaussian drive laser to irradiate a plasma binary phase square spiral zone plate (BPSSZP). Based on three-dimensional particle-in-cell (3D-PIC) simulations, we find that the drive laser has a phase difference of π after passing through the BPSSZP, ultimately generating the vortex laser with unique square symmetry. Quantitatively, by employing a drive laser pulse with intensity of 1.3 × 10 18 ~W/cm 2 , a vortex laser with intensity up to 1.8 × 10 19 ~W/cm 2 , and energy conversion efficiency of 18.61% can be obtained. The vortex lasers generated using the BPSSZP follow the modulo-4 transmutation rule when varying the topological charge of BPSSZP. Furthermore, the plasma-based BPSSZP has exhibited robustness and the ability to withstand multiple ultra-intense laser pulses. As the vortex laser generated via the BPSSZP has high intensity and large energy conversion efficiency, our scheme may hold potential applications in the community of laser-plasma, such as particles acceleration, intense high-order vortex harmonic generation, and vortex X/γ-ray sources.

The copropagation of two relativistic intense laser beams with orthogonal polarization in a parabolic plasma channel is studied analytically and numerically. A set of coupled equations for the evolution of the laser spot sizes and transverse centroids are derived by use of the variational approach. It is shown that the centroids of the two beams can spiral and oscillate around each other along the channel axis, where the characteristic frequency is determined both by the laser and plasma parameters. The results are verified by direct numerical solution of the relativistic nonlinear Schrödinger equations for the laser envelopes as well as three-dimensional particle-in-cell simulations. In the case with two ultrashort laser pulses when laser wakefields are excited, it is shown that the two wake bubbles driven by the laser pulses can spiral and oscillate around each other in a way similar to the two pulses. This can be well controlled by adjusting the incidence angle and separation distance between the two laser pulses. Preliminary studies show that externally injected electron beams can follow the trajectories of the oscillating bubbles. Our studies suggest a new way to control the coupling of two intense lasers in plasma for various applications, such as electron acceleration and radiation generation.