Extreme Gamma-Ray Flash in the λ³ Regime

During the next decades lasers with power approximately 100 petawatt are expected. These

lasers can provide the ultralelativistic intensities needed to study the collective behaviour of

γ-photons and electron-positron pairs. These ultralelativistic intensities can be achieved by focusing

down the laser beam to the sub-wavelength limit. In the past, a preplasma was found to

increase the g-photon energy conversion efficiency [1, 2]. In the present work, we employ three

dimensional quantum electrodynamic [3] particle in cell simulations where a single-cycle pulse

is focused by an 1/3 f-number parabola to a spherical-like field, in the so-called λ³ regime

[4]. The field interacts with a steep gradient foil target, resulting in a laser to γ-photon energy

conversion efficiency of almost 50 % at a laser intensity of 10²⁵ W cm⁻². A multiparametric

study on the target thickness and electron number density is performed. In addition, the dependency

on the laser polarisation is studied, revealing that a radially polarised laser is beneficial

on γ-photon generation compared to both linearly and azimuthally polarised lasers. The effect

of altering the laser power in the range 1−300 PW is also studied, revealing a region where a

prolific electron-positron pair generation happens, while γ-photon energy conversion efficiency

saturates. Finally, further interactions of the γ-photon flash with high-Z materials is studied by

the use of Mote-Carlo simulations.

References:

[1] T. Nakamura et al., Phys. Re. Lett. 108, 195001 (2012)

[2] K. V. Lezhnin et al., Phys. Plasmas 25, 123105 (2018)

[3] C. P. Ridgers et al., Phys. Rev. Lett. 108, 165006 (2012)

[4] G. Mourou et al., Plasma Phys. Rep. 28, 12 (2002)

[5] P. Hadjisolomou et al., Phys. Rev. E 104, 015203 (2021)