PIC Simulation Of Ultra-bright γ-ray Emission And Dense Positron Bunch Production In Interaction Between PW Laser-foil Interaction

With the construction of multi-PW laser facilities such as Extreme Light Infrastructure（ELI）and Shanghai Super-intense Ultrafast Laser Facility（SULF）,the laser intensity above 10²33 W/cm² will be accessible in the next few years.In the interaction between a laser at such an intensity and matter,the electron dynamics enters into a highly nonlinear regime dominated by radiation reaction and quantum electrodynamics（QED）effects.The strong nonlinear relativistic motion of electrons in ultraintense laser field emit bright energetic photons.The emitted high-energy photons may also induce secondary radiation and produce dense positron bunches.This paper focuses mainly on the production of ultra-brightγ-ray and dense positron bunch between laser-foil interaction.The main contents are presented as follow:Firstly,we propose to produce dense positron beams by using two obliquely incident ultra-intense lasers irradiating a flat aluminum target.It is found that by using two obliquely incident lasers,the pair production via the BW process can be significantly enhanced.When two lasers with intensities of 4×10²33 W/cm² are incident on the solid target at an oblique angle ofπ/12,the number of produced positrons exceeds 3×10¹⁰,which is increased by fifty times compared to that obtained using single laser with the same intensity.The robustness of the pair production with two obliquely incident lasers is further demonstrated.It is shown that the laser energy conversion efficiency decreases with the increase of oblique incident angle.Secondly,We investigate a novel scheme for attosecondγ-rays emission and dense positrons production by using multi-dimensional particle-in-cell simulations with quantum electrodynamics effects incorporated.By irradiating a p-polarized laser pulse onto a micro-wire array,electrons are rapidly dragged out of the micro-wire array and are efficiently accelerated to above GeV energy by the laser direction acceleration.When these electrons undergo betatron oscillation and Compton backscattering,ultra-brightγ-ray flashes are emitted with extremely short durations of⁴00 as.Theseγ-ray photons collide with the reflected laser,triggering the multi-photon Breit-Wheeler process.As a result,overdense pair bunches are produced with high yield of 4.4×10¹⁰.It is found that the scheme can result in highly efficient laser energy conversion.For optimal target geometry,the energy conversion from laser toγ-rays and to positrons approach 15%and 0.19%,respectively.The ultra-brightγ-rays and dense positrons generated by this scheme have a broad prospect in high energy density physics and attosecond nuclear physics.