Generation of MeV electrons and positrons with femtosecond pulses from a table-top laser system

Abstract

In experiments, the feasibility was demonstrated of generating multi-MeV electrons in a form of a collimated beam utilizing a table-top laser system delivering 200 fs pulses with P L ϭ1.2 TW and 10 Hz capability. The method uses the process of relativistic self-channeling in a high-density gas jet producing electron densities in the range of 3ϫ1019 -6ϫ10 20 cm Ϫ3 . In a thorough investigation, angularly resolved and absolutely calibrated electron spectra were measured and their dependence on the plasma density, laser intensity, and gas medium was studied. For the optimum electron density of n e ϭ2ϫ10 20 cm Ϫ3 the effective temperature of the electron energy distribution and the channel length exhibit a maximum of 5 MeV and 400 m respectively. The laser-energyto-MeV-electron efficiency is estimated to be 5%. In a second step, utilizing the multi-MeV electron beam anti-particles, namely positrons, were successfully generated in a 2 mm Pb converter. The average intensity of this new source of positrons is estimated to be equivalent to a radioactivity of 2ϫ10 8 Bq and it exhibits a very favorable scaling for higher laser intensities.

Overview of laser-driven generation of electron–positron beams

“…This approach was first adopted during a series of pioneering experiments by Gahn and collaborators (Gahn et al 2000(Gahn et al , 2002 whereby an ultra-short (duration of 130 fs) and low-energy laser pulse (energy of the order of 200 mJ) was focussed at the edge of a high-density gas-jet with an electron density of the order of 0.3 n c where n c represent the plasma critical density (n c ≈ 1.7 × 10 21 cm −3 for 790 nm light). In this regime, electrons are predominantly accelerated by direct laser acceleration (Pukhov et al 1999).…”

Coherent combs of antimatter from nonlinear electron-positron-pair creation

“…The first laser-driven positron beams have been achieved with energies less than 5MeV [6]. The following experiments reached positron energies up to 20MeV [7][8][9]. Most recently, positron beams with energies up to 120MeV have been produced in an all-optical setup experiment carried out at the Hercules laser facility [10,11].…”

Intense laser pair creation and applications

“…Liang [7] proposed much higher pair density may be achievable in principle using double-sided irradiation. Other proposals involve using circularly polarized lasers, precompressing the high-Z target, and using the laser wakefield acceleration mechanism [8] to make MeV electrons in a gas jet before converting them into pairs via separate high-Z target [9]. A major milestone was achieved recently by Chen et al [1] using the Titan laser at LLNL irradiating thick (wmm's) gold foils.…”