arXiv subjects

Longqing Yi

Publications and source records attributed to Longqing Yi.

At least 19 recordsLinked to original sources

arXiv2026

Detecting Quantum Stochastic Effects in Radiation Reaction via Laser-Produced Surface QED Plasmas

We propose a method to detect quantum stochastic effects in radiation reaction by irradiating a V-shaped plasma cavity with an ultra-intense laser pulse. The pulse accelerates GeV electrons along the inner surface and simultaneously drives strong-field surface wave near the cavity apex. The accelerated electron bunches then collide with the surface wave, the latter acts as an effective counter-propagating ultra-intense electromagnetic wave, triggering significant radiation reaction. Importantly, because the surface wave is confined to an ultra-thin QED plasma layer (on the scale of the skin depth) where the expected number of hard photon emissions per electron is of order unity, stochastic effects are expected. Three-dimensional particle-in-cell simulations with different QED models show that radiation reaction strongly reshapes the angular distribution of high-energy electrons. In particular, electrons deflected by the surface wave experience strong radiation loss. However, compared with the semi-classical model, the stochastic QED model preserves a higher-energy component in the deflected beam, producing a clear angular-spectral signature, which potentially opens a pathway for experimental study of quantum stochastic effects in radiation reaction.

physics.plasm-ph↗

arXiv2026

Generating intense attosecond pulses and vectorizing polarization states from laser-plasma interactions

Vector beams with spatially structured polarization and intertwined spin-orbital angular momentum (SAM-OAM) provide powerful degrees of freedom for tailoring light-matter interactions. While such structured beams are well established in the visible and infrared regimes, extending them to the extreme-ultraviolet (EUV) and soft X-ray (SXR) domains at relativistic intensities remains a major challenge. Here, we investigate the generation of higher-order harmonic vector beams driven by relativistic laser-plasma interactions. Combining theoretical analysis with three-dimensional particle-in-cell simulations, we elucidate the underlying physical mechanisms governing the transfer and conversion of polarization and orbital angular momentum during harmonic generation. We demonstrate that both the polarization topology and OAM of the emitted harmonics can be deterministically controlled by the topological charges of the driving field. Owing to the intrinsic properties of vector beams, either few-cycle driving pulses or vector polarization gating applied to multi-cycle pulses enable the production of intense isolated attosecond pulses featuring spiral wavefronts and spatially tailored polarization states. These results establish a pathway toward high-intensity structured light sources in the EUV and SXR regimes and open new opportunities for ultrafast and strong-field light-matter interaction studies with engineered angular momentum.

physics.plasm-ph↗

arXiv2025

High-Harmonic Optical Vortex Generation from a Plasma Aperture

When a high-power, femtosecond, circularly polarized (CP) laser pulse is incident on a micrometer-scale aperture in a solid foil target, it drives surface plasma oscillation, generating high-order harmonic vortices in the diffracted light. However, this mechanism has so far only been studied theoretically under ideal conditions. In this work, we perform numerical studies on more realistic situations. In particular, we focus on a scenario where the laser is obliquely incident on the target surface to avoid the potential damage of the optics by the reflected light. We demonstrate that increasing oblique incidence angle, reducing target thickness, and improving laser contrast can enhance the harmonic conversion efficiency. However, the generated harmonic beams may contain both Laguerre-Gaussian (LG) (vortex) and non-LG components under non-ideal conditions. We show that they can be separated by their divergence, as the vortex components has smaller diverging angle. In addition, we have performed computational analyses on the harmonic divergence angles and topological charge spectra of vortex high-order harmonics under different conditions. These high-order harmonic pure LG modes can potentially be filtered out for wide range of fundamental and applied physics researches. This study provides valuable insights for the design and implementation of future experiments.

physics.plasm-ph↗

arXiv2025

Relativistic Oscillating Window Driven by an Intense Laguerre Gaussian Laser Pulse

High-order harmonic generation by the diffraction of an intense Laguerre-Gaussian (LG) laser beam through a small aperture is studied. It is found that the 2D peripheral electron dynamics on the rim can facilitate complex interplay between the spin and orbital angular momentum interaction, which leads to distinct selection rules for LG pulses with different polarization states. In particular, when the driver is linearly polarized, the harmonic beams no longer follow a simple orbital angular momentum conservation rule. Instead, multiple LG modes with different topological charges are produced in each harmonic beam, and the number of modes equals to the harmonic order. A theory is derived and validated by simulations, which can predict the harmonic topological charges as well as their relative intensities for LG drivers with different polarization states. Our work provides fundamental insight into the behavior of light in nonlinear optics, and paves the way towards high-intensity UV or X-ray pulses carrying controllable OAM, that can serve as versatile tools at frontiers of various scientific fields.

physics.plasm-ph↗

arXiv2025

Helical Electron Beam Micro-Bunching by High-Order Modes in a Micro-Plasma Waveguide

Electron acceleration by a high-power Laguerre-Gaussian pulse in a micro-plasma waveguide is investigated. When the incident laser travels in the waveguide, electrons on the wall are extracted into the vacuum core and accelerated by the longitudinal field of the waveguide mode. Using 3D particle-in-cell simulations, we demonstrate that high energy (~100 MeV) electron beams with extremely high charge (~10 nC), ultrashort duration (~30 fs) and small divergence (~1 deg) can be produced by a 100-TW, few-Joule class laser system. In particular, when the drive Laguerre-Gaussian pulse is circularly polarized, it excites high-order waveguide modes that exhibit helical longitudinal electric fields. The 3D profile of this accelerating field is imprinted into the high energy electron beam, leading to helical micro-bunching. This process can be controlled by the spin and orbital angular momentum of the drive pulse. This work paves the way to the generation of highcharge, relativistic electron beams with controlled helicity, which holds great potential for advances in fundamental science and a variety of applications.

physics.plasm-ph↗

arXiv2025

Anomalous Effects in Single-slit Diffraction of Light at Relativistic Intensities

High-order harmonic generation via single-slit diffraction of relativistic laser pulses is investigated. Using fully kinetic 2D and 3D particle-in-cell simulations, we show that interesting optical phenomena emerge, including the generation of harmonic beams that are anomalously polarized orthongal to the driver, harmonic spectrum variation depending on the incident laser polarization, and a deflection of transmitted lights that leads to a tilted harmonic intensity pattern. It is shown these anomalous effects are associated with complex peripheral electron dynamics on the plasma vacuum interface. To account for these effects, a new theoretical model is developed to calculate harmonic fields from arbitrary 2D electron motion within the diffraction plane, the results agree well with the simulations. Our model indicates that the optical properties of the harmonic beams are determined by the 2D in-plane electron motion, which can be leveraged to provide immense opportunities for manipulating light-matter interaction at relativistic intensities.

physics.plasm-ph↗

arXiv2025

High-Harmonic Generation and Optical Torque Interaction via Relativistic Diffraction of a Spatiotemporal Vortex Light

Diffraction of a relativistically-strong light can produce high-order harmonics via the relativistic oscillating window mechanism. In this process, the characteristics of the 2D electron dynamics at the diffraction screen can be imprinted to the generated harmonics, which provides abundant opportunities for manipulating light-matter interaction. In this work, we study single-slit diffraction of a high-intensity spatiotemporal optical vortex (STOV) - a beam carrying transverse orbital angular momentum (OAM). We demonstrate that due to the spatiotemporal structure of the driver, it induces differential electron oscillations on the screen, which conveys the transverse OAM to the high-order harmonic STOV beams. As a result, the topological charges of the harmonic beams are $l = nl_0$, where $l_0$ is the topological charge of the fundamental driving light, and $n$ is the harmonic order. In addition, we show that by controlling the slit angle with respect to the driver' s transverse OAM, the STOV light can exert a torque on the plasma, thus providing a way to manipulate the transverse OAM orientation of the generated harmonics.

physics.plasm-ph↗

arXiv2025

Inverse cascade from helical and nonhelical decaying columnar magnetic fields

Powerful lasers may in future produce magnetic fields that would allow us to study turbulent magnetohydrodynamic inverse cascade behavior. This has so far only been seen in numerical simulations. In the laboratory, however, the produced fields may be highly anisotropic. Here, we present corresponding simulations to show that, during the turbulent decay, such a magnetic field undergoes spontaneous isotropization. As a consequence, we find the decay dynamics to be similar to that in isotropic turbulence. We also find that an initially pointwise nonhelical magnetic field is unstable and develops magnetic helicity fluctuations that can be quantified by the Hosking integral. It is a conserved quantity that characterizes magnetic helicity fluctuations and governs the turbulent decay when the mean magnetic helicity vanishes. As in earlier work, the ratio of the magnetic decay time to the Alfv\'en time is found to be around $50$ in the helical and nonhelical cases. At intermediate times, the ratio can even reach a hundred. This ratio determines the endpoints of cosmological magnetic field evolution.

physics.plasm-ph↗

arXiv2024

Generation of isolated attosecond electron bunches by the diffraction of a polarization-tailored intense laser beam

We propose utilizing a polarization-tailored high-power laser pulse to extract and accelerate electrons from the edge of a solid foil target to produce isolated attosecond electron bunches. The laser pulse consists of two orthogonally-polarized components with a time delay comparable to the pulse duration, such that the polarization in the middle of the pulse rapidly rotates over 90$^\circ$ within few optical cycles. Three-dimensional (3D) Particle-in-Cell simulations show that when such a light pulse diffracts at the edge of a plasma foil, a series of isolated relativistic electron bunches are emitted into separated azimuthal angles determined by the varying polarization. In comparison with most other methods that require an ultra-short drive laser, we show the proposed scheme works well with typical multi-cycle ($\sim 30~$fs) pulses from high-power laser facilities. The generated electron bunches have typical durations of a few hundred attoseconds and charges of tens of picocoulombs.

physics.plasm-ph↗

arXiv2023

High-efficient harmonic vortex generation from a laser irradiated hollow-cone target

It has been recently reported that ultraviolet harmonic vortices can be produced when a high-power circular-polarized laser pulse travels through a micro-scale waveguide. However, the harmonic generation quenches typically after a few tens of microns of propagation, due to the build-up of electrostatic potential that suppresses the amplitude of the surface wave. Here we propose to utilize a hollow-cone channel to overcome this obstacle. When traveling in a cone target, the laser intensity gradually increases, allowing the surface wave to maintain a high amplitude for a much longer distance. The harmonic vortices can be produced with very high efficiency. According to three-dimensional particle-in-cell simulations, the overall efficiency are boosted by almost one order of magnitude, reaching $>20\%$. It is also found that using the cone targets can mitigate efficiency decline due to pre-heating of plasma by laser prepulse. The proposed scheme paves the way to the development of powerful optical vortices sources in the extreme ultraviolet regime - an area of significant fundamental and applied physics potential.

physics.plasm-ph↗

arXiv2022

Intense high-harmonic optical vortices generated from a micro-plasma-waveguide irradiated by a circularly polarized laser pulse

A scheme for generating intense high-harmonic optical vortices is proposed. It relies on spin-orbit interaction of light when a relativistically-strong circularly polarized laser pulse irradiates a micro-plasma-waveguide. The intense laser field drives a strong surface wave at the inner boundary of the waveguide, which leads to high-order harmonic generation as the laser traveling inside. For a circularly polarized drive laser, the optical chirality is imprinted to the surface wave, which facilitates conversion of spin angular momentum of the fundamental light into orbital angular momenta of the harmonics. A "shaken waveguide" model is developed showing that the aforementioned phenomena arises due to nonlinear plasma response that modifies electromagnetic mode at high intensities. We further show the phase velocities of all the harmonic beams are automatically matched to the driving laser, so that the harmonic intensities increase with propagation distance. The efficiency of harmonic production are related to the surface wave breaking effect, which can be significantly enhanced using a tightly focused laser. Our simulation suggests an overall conversion efficiency $\sim5\%$ can be achieved.

physics.plasm-ph↗

arXiv2021

High-Harmonic Generation and Spin-Orbit Interaction of Light in a Relativistic Oscillating Window

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 polarised, 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 $I_n\propto n^{-3.5}$ is produced for sufficiently intense laser beams, where $I_n$ is the intensity of the $n$th harmonic. This work opens up a new realm of possibilities for producing intense extreme ultraviolet vortices, and diffraction-based HHG studies at relativistic intensities.

physics.plasm-ph↗

arXiv2020

Driving positron beam acceleration with coherent transition radiation

Positron acceleration in plasma wakefield faces significant challenges since the positron beam must be pre-generated and precisely coupled into the wakefield, and most critically, suffers from defocusing issues. Here we propose a scheme that utilizes laser-driven electrons to produce, inject and accelerate positrons in a single set-up. The high-charge electron beam from wakefield acceleration creates copious electron-positron pairs via the Bethe-Heitler process, followed by enormous coherent transition radiation due to the electrons' exiting from the metallic foil. Simulation results show that the coherent transition radiation field reaches up to 10's GV m-1, which captures and accelerates the positrons to cut-off energy of 1.5 GeV with energy peak of 500 MeV and energy spread is about 24.3%. An external longitudinal magnetic field of 30 T is also applied to guide the electrons and positrons during the acceleration process. This proposed method offers a promising way to obtain GeV fast positron sources.

physics.plasm-ph↗

arXiv2020

Multimillijoule terahertz radiation from laser interactions with microplasma-waveguides

When a relativistic, femtosecond laser pulse enters a waveguide, the pulse energy is coupled into waveguide optical modes. The longitudinal laser field effectively accelerates electrons along the axis of the channel, while the asymmetric transverse electromagnetic fields tend to expel fast electrons radially outwards. At the exit of the waveguide, the $\sim$${\rm nC}$, $\sim$$10\ {\rm MeV}$ electron bunch converts its energy to a $\sim$$10\ {\rm mJ}$ terahertz (THz) laser pulse through coherent diffraction radiation. In this paper, we present 3D particle-in-cell simulations and theoretical analyses of the aforementioned interaction process. We investigate the process of longitudinal acceleration and radial expulsion of fast electrons, as well as the dependence of the properties of the resulting THz radiation on laser and plasma parameters and the effects of the preplasma. The simulation results indicate that the conversion efficiency of energy can be over $5\%$ if the waveguide length is optimal and a high contrast pump laser is used. These results guide the design of more intense and powerful THz sources.

physics.plasm-ph↗

arXiv2020

Highly-efficient terahertz radiation generated by surface electrons from laser-foil interactions

A novel scheme for generating powerful terahertz (THz) radiation based on laser-solid interactions is proposed. When a $p$-polarized femtosecond laser impinges obliquely on a plane solid target and the target partially blocks the laser energy, surface electrons are extracted out and accelerated by the laser fields, forming a low-divergence electron beam. A half-cycle THz radiation pulse is emitted simultaneously as the beam passes by the edge of the target, due to coherent diffraction radiation. Our particle-in-cell simulations show that the relativistic THz pulse can have an energy of a few tens of millijoule and the conversion efficiency can be over 1$\%$ with existing $\sim$J level femtosecond laser sources.

physics.plasm-ph↗

arXiv2019

Spin-orbit interaction in a high-power laser irradiated micro-scale plasma waveguide

Light carries angular momentum as spin and orbital components. The spin-orbit interaction (SOI) of light refers to phenomena in which the spin (left or right circular polarisation) affects the spatial degrees of freedom. Recently, interest in SOI has surged, as it provides physical insight into the behaviour of polarised light at subwavelength scales, and allows for spin-controlled manipulation of light. Most studies are performed with low intensity, leaving the role SOI plays in the relativistic laser-plasma interaction, characterised by nonlinearity, less understood. Here, using 3D particle-in-cell simulations, we report SOI effects in this unprecedented regime. Specifically, a circularly polarised Gaussian laser irradiating a micro-scale plasma waveguide drives a spin-controlled chiral surface wave, allowing the reflected harmonic photons to gain orbital angular momentum (OAM). These effects produce intense optical vortices in the extreme ultraviolet regime - an area of significant fundamental and applied physics potential.

physics.plasm-ph↗

arXiv2019

Proton Acceleration in a Laser-induced Relativistic Electron Vortex

We show that when a solid plasma foil with a density gradient on the front surface is irradiated by an intense laser pulse at a grazing angle, around 80 degrees, a relativistic electron vortex is excited in the near-critical-density layer after the laser pulse depletion. The vortex structure and dynamics are studied using particle-in-cell simulations. Due to the asymmetry introduced by nonuniform background density, the vortex drifts at a constant velocity, typically 0.2 to 0.3 times the speed of light. The strong magnetic field inside the vortex leads to significant charge separation; in the corresponding electric field initially stationary protons can be captured and accelerated to twice the velocity of the vortex (100-200 MeV). A representative scenario - with laser intensity of 10^21 W/cm^2 -is discussed: two dimensional simulations suggest that a quasi-monoenergetic proton beam can be obtained with a mean energy 140 MeV and an energy spread of about 10%. We derive an analytical estimate for the vortex velocity in terms of laser and plasma parameters, demonstrating that the maximum proton energy can be controlled by the incidence angle of the laser and the plasma density gradient.

physics.plasm-ph↗

arXiv2019

Coherent diffraction radiation of relativistic terahertz pulses from a laser-driven micro-plasma-waveguide

We propose a method to generate isolated relativistic terahertz (THz) pulses using a high-power laser irradiating a mirco-plasma-waveguide (MPW). When the laser pulse enters the MPW, high-charge electron bunches are produced and accelerated to ~ 100 MeV by the transverse magnetic modes. A substantial part of the electron energy is transferred to THz emission through coherent diffraction radiation as the electron bunches exit the MPW. We demonstrate this process with three-dimensional particle-in-cell simulations. The frequency of the radiation is determined by the incident laser duration, and the radiated energy is found to be strongly correlated to the charge of the electron bunches, which can be controlled by the laser intensity and micro-engineering of the MPW target. Our simulations indicate that 100-mJ level relativistic-intense THz pulses with tunable frequency can be generated at existing laser facilities, and the overall efficiency reaches 1%.

physics.plasm-ph↗