arXiv subjects

Qianyi Ma

Publications and source records attributed to Qianyi Ma.

8 recordsLinked to original sources

arXiv2026

Effects of realistic laser intensity and phase distribution on high-charge laser wakefield acceleration

Laser wakefield acceleration (LWFA) can produce relativistic electron beams and various secondary particles in centimeter-long plasmas, making it a valuable particle source with important applications in many disciplines. In this work, we examine the effects of non-ideal transverse intensity and phase distribution of laser pulses on LWFA through both experimental measurements and particle-in-cell simulations. The complex transverse profile of the 75 TW laser pulses reduces the self-focused intensity in plasma compared with a transversely Gaussian laser. Furthermore, the sheath structure of the nonlinear plasma wake excited by realistic laser pulses is wider and more complicated than that of a Gaussian laser. These hinder the injection of the plasma electrons. As the laser pulse propagates through the plasma, its intensity profile gradually becomes elliptical and drives a plasma wake with a sharp sheath near the azimuths of the major axis, leading to an injection. When using a realistic laser profile in simulations, both the charge and energy of injected electrons closely match experimental results ($\sim200$ pC of charge and $\sim 200$ MeV peak energy), whereas the Gaussian laser simulations produce much higher charge ($\sim500$ pC). Our findings reveal the difference in injection dynamics between LWFA driven by non-ideal laser pulses and those driven by Gaussian pulses, and are useful for applications of LWFA which demand high-charge electron beams.

physics.plasm-ph↗

arXiv2026

Nanometer-scale pre-bunched electron beams generated from all-optical plasma-based acceleration

High-quality and prebunched electron beams can produce coherent x-rays with high intensity and narrow bandwidth, which is essential for modern light sources. An all-optical scheme based on plasma-based acceleration to produce bright electron beams that are pre-bunched on nanometer-scales is proposed. By using a density modulation created by two low intensity counter-propagating lasers, the phase velocity of the plasma wake excited by an intense driver laser in a uniform plasma can be modulated at a frequency twice that of the colliding lasers and thus turn the injection on and off. The injected electrons are micro-bunched at the Doppler shifted wavelength of the modulated wavelength using the corresponding phase velocity of the gradual expansion of the wakefield. It is demonstrated that by controlling the properties of the drive and colliding lasers, that beams with exotic pre-bunched structures can be produced, which may have critical applications in ultrafast high power x-rays. This extremely compact, all-optical scheme to produce ultra-bright pre-bunched electron beams may therefore enable novel applications for ultrafast x-ray users and arouse general interest in various fields.

physics.acc-ph↗

arXiv2025

Optimization of laser-driven proton acceleration in a near-critical-density plasma

Optimizing laser and plasma parameters is crucial for enhancing accelerated proton energy in laser-driven proton acceleration with finite laser energy for applications such as cancer therapy. Tight focusing plays a significant role in improving laser-driven proton acceleration, which is generally believed as a result of the enhancement of laser intensity. However, we find that even at a fixed laser intensity, reducing the focal spot size still enhances the proton energy. Through particle-in-cell simulations and theoretical modeling, we find that at a small spot size (0.8 {\mu}m), the maximum proton energy is enhanced by 56.3% compared to that obtained at a conventional spot size (3 {\mu}m). This improvement is attributed to the dominance of ponderomotive-force-driven electrons at reduced spot sizes, which generate stronger charge-separation fields that propagate at higher velocities. Furthermore, to optimize proton acceleration, we analytically derive an ideal plasma density profile that promotes phase-stable proton acceleration, yielding an additional energy increase of 61.3% over the case of a tightly focused laser interacting with a planar target of uniform density. These findings remain robust under parameter variations, indicating that advanced focusing techniques combined with optimized plasma profiles could relax the demand for high laser energies, thereby reducing the reliance on large-scale laser facilities in medical and scientific applications.

physics.plasm-ph↗

arXiv2025

Generating 10 GW-class isolated zeptosecond x-ray bursts through bootstrapping two plasma-based accelerator stages

A method is proposed to generate coherent, intense zeptosecond x-ray pulses by using the electron beam produced by a laser wakefield accelerator (LWFA) stage as the driver for a beam driven plasma wakefield accelerator (PWFA) stage. The LWFA injector stage requires a readily available 100 TW laser driver to produce a GeV class self-injected electron beam. This beam is focused and used as the driver in a PWFA stage that utilizes a solid-density plasma with a modulated density downramp. The concept is shown to be capable of producing an ultra-short electron beam with unprecedented density ($10^{26}~\mathrm{cm^{-3}}$) and brightness ($ 10^{24}~\ampere/\meter^2/\radian ^2$), that is also pre-bunched on 0.1 Angstrom scales. By colliding this pre-bunched extreme beam with an optical undulator, an intense zeptosecond pulse can be emitted if the spatially focusing region is matched with the lasing region of the beam. Multi-dimensional particle-in-cell simulations are performed of the entire concept to demonstrate that an isolated 10 GW-class zeptosecond pulse with a full-width-half-maximum duration of 700 zs can be generated in a tapered laser pulse. Such an intense zeptosecond pulse generation scheme may provide an essential probe for nuclear physics and quantum electrodynamics processes.

physics.acc-ph↗

arXiv2024

Ultra-short lifetime isomer studies from photonuclear reactions using laser-driven ultra-intense γ-ray

Isomers, ubiquitous populations of relatively long-lived nuclear excited states, play a crucial role in nuclear physics. However, isomers with half-life times of several seconds or less barely had experimental cross section data due to the lack of a suitable measuring method. We report a method of online γ spectroscopy for ultra-short-lived isomers from photonuclear reactions using laser-driven ultra-intense γ-rays. The fastest time resolution can reach sub-ps level with γ-ray intensities >10^{19}/s ({\geqslant} 8 MeV). The ^{115}In(γ, n)^{114m2}In reaction (T_{1/2} = 43.1 ms) was first measured in the high-energy region which shed light on the nuclear structure studies of In element. Simulations showed it would be an efficient way to study ^{229m}Th (T_{1/2} = 7 μs), which is believed to be the next generation of nuclear clock. This work offered a unique way of gaining insight into ultra-short lifetimes and promised an effective way to fill the gap in relevant experimental data.

nucl-ex↗

arXiv2023

On the generation of attosecond gigawatt soft X-ray pulses through coherent Thomson backscattering

Collision between relativistic electron sheets and counter-propagating laser pulses is recognized as a promising way to produce intense attosecond X-rays through coherent Thomson backscattering (TBS). In a double-layer scheme, the electrons in an ultrathin solid foil are first pushed out by an intense laser driver and then interact with the laser reflected off a second foil to form a high-density relativistic electron sheet with vanishing transverse momentum. However, the repulsion between these concentrated electrons can increase the thickness of the layer, reducing both its density and subsequently the coherent TBS. Here, we present a systematic study on the evolution of the flying electron layer and find that its resulting thickness is determined by the interplay between the intrinsic space-charge expansion and the velocity compression induced by the drive laser. How the laser driver, the target areal density, the reflector and the collision laser intensity affect the properties of the produced X-rays is explored. Multi-dimensional particle-in-cell simulations indicate that employing this scheme in the nonlinear regime has the potential to stably produce soft X-rays with several GW peak power in hundreds of TW ultrafast laser facilities. The pulse duration can be tuned to tens of attoseconds. This compact and intense attosecond X-ray source may have broad applications in attosecond science.

physics.plasm-ph↗

arXiv2023

On the generation of ultra-bright and low energy spread electron beams in laser wakefield acceleration in a uniform plasma

The quality of electron beams produced from plasma-based accelerators, i.e., normalized brightness and energy spread, has made transformative progress in the past several decades in both simulation and experiment. Recently, full-scale particle-in-cell (PIC) simulations have shown that electron beams with unprecedented brightness ($10^{20}\sim10^{21}~\mathrm{A}/\mathrm{m}^2/\mathrm{rad}^2$) and $0.1\sim 1$ MeV energy spread can be produced through controlled injection in a slowly expanding bubble that arises when a particle beam or laser pulse propagates in density gradient, or when a particle beam self-focuses in uniform plasma or has a superluminal flying focus. However, in previous simulations of work on self-injection triggered by an evolving laser driver in a uniform plasma, the resulting beams did not exhibit comparable brightnesses and energy spreads. Here, we demonstrate through the use of large-scale high-fidelity PIC simulations that a slowly expanding bubble driven by a laser pulse in a uniform plasma can indeed produce self-injected electron beams with similar brightnesses and energy spreads as for an evolving bubble driven by an electron beam driver. We consider laser spot sizes roughly equal to the matched spot sizes in a uniform plasma and find that the evolution of the bubble occurs naturally through the evolution of the laser. The effects of the electron beam quality on the choice of physical as well as numerical parameters, e.g. grid sizes and field solvers used in the PIC simulations are presented. It is found that this original and simplest injection scheme can produce electron beams with beam quality exceeding that of the more recent concepts.

physics.acc-ph↗

arXiv2022

Production of multi-oriented polarization for relativistic electron beams via a mutable filter for nonlinear Compton scattering

We propose a feasible scenario to directly polarize a relativistic electron beam and obtain overall polarization in various directions through a filter mechanism for single-shot collision between an ultrarelativistic unpolarized electron beam and an ultraintense circularly polarized laser pulse. The electrons are scattered to a large angular range of several degrees and the polarization states of the electrons are connected with their spatial position after the collision. Therefore, we can employ a filter to filter out a part of the scattered electrons based on their position and obtain high-degree overall polarization for the filtered beam. Through spin-considered Monte-Carlo simulations, polarization with a degree up to 62% in arbitrary transverse directions and longitudinal polarization up to 10% are obtained for the filtered beams at currently achievable laser intensity. We theoretically analyze the distribution formation of the scattered electrons and investigate the influence of different initial parameters through simulations to demonstrate the robustness of our scheme. This scenario provides a simple and flexible way to produce relativistic polarized electron beams for various polarization directions.

physics.acc-ph↗