arXiv subjects

Huai-Hang Song

Publications and source records attributed to Huai-Hang Song.

12 recordsLinked to original sources

arXiv2026

Generation of Isolated Collimated Polarized $γ$-ray Beams via Spatiotemporal Optical Vortex Modulation

Attosecond, collimated, bright, polarized $γ$-ray sources are in high demand across nuclear physics, astrophysics, and high-energy physics. However, realizing attosecond duration, high collimation, high brilliance, and high polarization simultaneously within a single isolated source remains an outstanding challenge, owing to the inherent trade-offs between beam trapping and radiative dynamics. Here, we propose a novel scheme to generate an isolated, collimated, high-brilliance, polarized attosecond $γ$-ray beam from conventional solid foils irradiated by a linearly polarized spatiotemporal optical vortex (STOV) laser pulse accessible in Lab. Three-dimensional spin-resolved particle-in-cell simulations reveal that this relativistic-intensity STOV pulse can trap and accelerate electrons at its spatiotemporal singularity, producing a compact isolated electron bunch. This electron bunch subsequently undergoes head-on collision with the reflected laser pulse, which generates isolated $γ$-ray beams through nonlinear Compton scattering. With a peak intensity of $7\times10^{21}$ W/cm$^2$, we observe an isolated collimated ($\sim1.5^{\circ}$) $γ$-ray beam with an average linear polarization of $>60\%$ and a duration of $\sim$500 attoseconds. This approach is feasible with current or upcoming laser facilities and robust against variations in laser and target parameters, highlighting the capability of spatiotemporal structured light field modulation to address outstanding problems in plasma physics.

physics.plasm-ph↗

arXiv2026

Probing vacuum birefringence in an Ultrastrong Laser Field via High-energy Gamma-ray Polarimetry

Vacuum birefringence (VB), a fundamental prediction of nonlinear quantum electrodynamics (QED), has eluded direct laboratory detection due to its extreme weakness. We propose a compact, "self-probing" scheme where a GeV electron beam collides head-on with a petawatt laser pulse. Circularly polarized gamma-ray photons, generated via nonlinear Compton scattering in the same pulse, then probe the birefringent vacuum it induces. This integrated design bypasses the stringent synchronization and beam transport requirements of traditional pump-probe setups. Our nonperturbative strong-field QED simulations reveal a clear VB signature: conversion of circular to linear polarization, with the induced Stokes parameter $S_1$ reaching ~0.019 within the selected angular range. This corresponds to a refractive index difference $Δn = 1.829 \times 10^{-4}$ over micron-scale paths, directly measurable as a high-contrast "X-shape" asymmetry in $e^+e^-$ pair distributions. The scheme provides a feasible path to first laboratory VB detection with current laser and accelerator technologies.

physics.plasm-ph↗

arXiv2025

Photon-polarization-resolved linear Breit-Wheeler pair production in a laser-plasma system

The linear Breit-Wheeler (LBW) process, mediated by photon-photon collisions, can emerge as the dominant pair production mechanism in the ultraintense laser-plasma interaction for laser intensities below $10^{23}~\rm W/cm^2$. Here, we explore the role of photon polarization in LBW pair production for a 10 PW-class, linearly polarized laser interacting with a solid-density plasma. The motivation for this investigation lies in two main aspects: photons emitted via nonlinear Compton scattering are inherently linearly polarized, and the LBW process exhibits a distinct sensitivity to photon polarization. By leveraging particle-in-cell simulations that self-consistently incorporate photon-polarization-resolved LBW pair production, our results reveal that photon polarization leads to a 5\% to 10\% reduction in the total LBW positron yield. This suppression arises because the polarization directions of the colliding photons are primarily parallel to each other, resulting in a diminished LBW cross section compared to the unpolarized case. The influence of photon polarization weakens as the laser intensity increases.

physics.plasm-ph↗

arXiv2025

Detecting Linear Breit-Wheeler Signals with a Laser-Foil Setup

As a fundamental QED process, linear Breit-Wheeler (LBW) pair production predicted 90 years ago has not yet been demonstrated in experiments with real photons. Here, we propose an experimentally advantageous scheme to detect the LBW signal by irradiating a foil target with a single 10 PW-level laser. Our integrated QED particle-in-cell simulations demonstrate that the LBW signal can be explicitly distinguished from the Bethe-Heitler (BH) signal by comparing positron energy spectra behind the target at varying target thicknesses. The LBW positrons are created at the front of the target and subsequently experience both laser vacuum acceleration and sheath field acceleration to gain high energies, while BH positrons, originating within the target bulk, are only subjected to sheath field acceleration. As a result, the invariance of the high-energy tail of positron spectra with respect to the target thickness serves as a distinct signature of the LBW process. Notably, this scheme remains viable even when the BH yield dominates over the LBW yield.

physics.plasm-ph↗

arXiv2024

Polarized QED Cascades over Pulsar Polar Caps

The formation of $e^\pm$ plasmas within pulsar magnetospheres through quantum electrodynamics (QED) cascades in vacuum gaps is widely acknowledged. This paper aims to investigate the effect of photon polarization during the QED cascade occurring over the polar cap of a pulsar. We employ a Monte Carlo-based QED algorithm that accurately accounts for both spin and polarization effects during photon emission and pair production in both single-particle and particle-in-cell (PIC) simulations. Our findings reveal distinctive properties in the photon polarization of curvature radiation (CR) and synchrotron radiation (SR). CR photons exhibit high linear polarization parallel to the plane of the curved magnetic field lines, whereas SR photons, on average, demonstrate weak polarization. As the QED cascade progresses, SR photons gradually dominate over CR photons, thus reducing the average degree of photon polarization. Additionally, our study highlights an intriguing observation: the polarization of CR photons enhances $e^\pm$ pair production by approximately 5%, in contrast to the inhibition observed in laser-plasma interactions. Our self-consistent QED PIC simulations in the corotating frame reproduce the essential results obtained from single-particle simulations.

astro-ph.HE↗

arXiv2023

From linear to nonlinear Breit-Wheeler pair production in laser-solid interactions

During the ultraintense laser interaction with solids (overdense plasmas), the competition between two possible quantum electrodynamics (QED) mechanisms responsible for $e^\pm$ pair production, i.e., linear and nonlinear Breit-Wheeler (BW) processes, remains to be studied. Here, we have implemented the linear BW process via a Monte Carlo algorithm into the QED particle-in-cell (PIC) code YUNIC, enabling us to self-consistently investigate both pair production mechanisms in the plasma environment. By a series of 2D QED-PIC simulations, the transition from the linear to the nonlinear BW process is observed with the increase of laser intensities in the typical configuration of a linearly polarized laser interaction with solid targets. A critical normalized laser amplitude about $a_0\sim$ 400-500 is found under a large range of preplasma scale lengths, below which the linear BW process dominates over the nonlinear BW process. This work provides a practicable technique to model linear QED processes via integrated QED-PIC simulations. Moreover, it calls for more attention to be paid to linear BW pair production in near future 10-PW-class laser-solid interactions.

physics.plasm-ph↗

arXiv2021

Dense Polarized Positrons from Laser-Irradiated Foil Targets in the QED Regime

Dense positrons are shown to be effectively generated from laser-solid interactions in the strong-field quantum electrodynamics (QED) regime. Whether these positrons are polarized has not yet been reported, limiting their potential applications. Here, by QED particle-in-cell simulations including electron-positron spin and photon polarization effects, we investigate a typical laser-solid setup that an ultraintense linearly polarized laser irradiates a foil target with $μ$m-scale-length preplasma. We find that once the positron yield becomes appreciable with the laser intensity exceeding $10^{24}~\rm W/\rm cm^2$, the positrons are obviously polarized. The polarized positrons can acquire $>30\%$ polarization degree and $>30$ nC charge with a flux of $10^{12}\,{\rm sr}^{-1}$. The polarization relies on the deflected angles and can reach 60\% at some angles and energies. The angularly-dependent polarization is attributed to the asymmetrical laser fields positrons undergo in the skin layer of overdense plasma, where the radiative spin-flip and radiation reaction play significant roles. The positron polarization is robust and could generally appear in future 100-PW-class laser-solid experiments for various applications.

physics.plasm-ph↗

arXiv2021

YUNIC: A Multi-Dimensional Particle-In-Cell Code for Laser-Plasma Interaction

For simulating laser-plasma interactions, we developed a parallel, multi-dimensional, fully relativistically particle-in-cell (PIC) code, named YUNIC. The core algorithm is introduced, including field solver, particle pusher, field interpolation, and current interpolation. In addition to the classical electromagnetic interaction in plasmas, nonlinear Compton scattering and nonlinear Breit-Wheeler pair production are also implemented based on Monte-Carlo methods to study quantum electrodynamics (QED) processes. We benchmark YUNIC against theories and other PIC codes through several typical cases. YUNIC can be applied in varieties of physical scenes, from relativistic laser-plasma interactions to astrophysical plasmas and strong-field QED physics.

physics.plasm-ph↗

arXiv2021

Generation of polarized positron beams via collisions of ultrarelativistic electron beams

A novel scheme is proposed for generating a polarized positron beam via multiphoton Breit-Wheeler process during the collision of a 10 GeV, pC seeding electron beam with the other 1 GeV, nC driving electron beam. The driving beam provides the strong self-generated field, and a suitable transverse deviation distance between two beams enables the field experienced by the seeding beam to be unipolar, which is crucial for realizing the positron polarization. We employ the particle simulation with a Monte-Carlo method to calculate the spin- and polarization-resolved photon emission and electron-positron pair production in the local constant field approximation. Our simulation results show that a highly polarized positron beam with polarization above $40\%$ can be generated in several femtoseconds, which is robust with respect to parameters of two electron beams. Based on an analysis of the influence of $γ$-photon polarization on the polarized pair production, we find that a polarized seeding beam of the proper initial polarization can further improve the positron polarization to $60\%$.

physics.acc-ph↗

arXiv2021

Spin and polarization effects on the nonlinear Breit-Wheeler pair production in laser-plasma interaction

The spin effect of electrons/positrons ($e^-$/$e^+$) and polarization effect of $γ$ photons are investigated in the interaction of two counter-propagating linearly polarized 10-PW-class laser pulses with a thin foil target. The processes of nonlinear Compton scattering and nonlinear Breit-Wheeler pair production based on spin- and polarization-resolved probabilities are implemented into the particle-in-cell (PIC) algorithm by Monte Carlo methods. It is found from PIC simulations that the average degree of linear polarization of emitted $γ$ photons can exceed $50\%$. This polarization effect leads to reduced positron yield by about $10\%$. At some medium positron energies, the reduction can reach $20\%$. Furthermore, we also observe that the local spin polarization of $e^-$/$e^+$ leads to a slight decrease of the positron yield about $2\%$ and some anomalous phenomena about the positron spectrum and photon polarization at the high-energy range, due to spin-dependent photon emissions. Our results indicate that spin and polarization effects should be considered in calculating the pair production and laser-plasma interaction with the laser power of 10-PW class.

physics.plasm-ph↗

arXiv2020

Low-frequency whistler waves excited by relativistic laser pulses

It is shown by multi-dimensional particle-in-cell simulations that intense secondary whistler waves with special vortex-like field topology can be excited by a relativistic laser pulse in the highly magnetized, near-critical density plasma. Such whistler waves with lower frequencies obliquely propagate on both sides of the laser propagation axis. The energy conversion rate from laser to whistler waves can exceed 15%. Their dispersion relations and field polarization properties can be well explained by the linear cold-plasma model. The present work presents a new excitation mechanism of whistler modes extending to the relativistic regime and could also be applied in magnetically assisted fast ignition.

physics.plasm-ph↗

arXiv2019

Spin-polarization effects of an ultrarelativistic electron beam in an ultraintense two-color laser pulse

Spin-polarization effects of an ultrarelativistic electron beam head-on colliding with an ultraintense two-color laser pulse are investigated comprehensively in the quantum radiation-dominated regime. We employ a Monte Carlo method, derived from the recent work of [Phys. Rev. Lett. {\bf 122}, 154801 (2019)], to calculate the spin-resolved electron dynamics and photon emissions in the local constant field approximation. We find that electron radiation probabilities in adjacent half cycles of a two-color laser field are substantially asymmetric due to the asymmetric field strengths, and consequently, after interaction the electron beam can obtain a total polarization of about 11\% and a partial polarization of up to about 63\% because of radiative spin effects, with currently achievable laser facilities, which may be utilized in high-energy physics and nuclear physics. Moreover, the considered effects are shown to be crucially determined by the relative phase of the two-color laser field and robust with respect to other laser and electron beam parameters.

physics.plasm-ph↗