Description
The emergence of multi-petawatt laser systems enables access to the quantum electrodynamics regime [T. Nakamura et al., Phys. Rev. Lett. 108, 195001 (2012), C. P. Ridgers et al., Phys. Rev. Lett. 108, 165006 (2012)], where intense laser-matter interactions lead to prolific $\gamma$-photon emission and electron-positron pair production. In [P. Hadjisolomou et al., Phys. Rev. E 104, 015203 (2021), P. Hadjisolomou et al., J. Plasma Phys. 88, 1 (2022)], we use three-dimensional particle-in-cell simulations to investigate the interaction of tightly focused, single-cycle pulses with thin foil targets. This so-called $\lambda^3$ regime [G. Mourou et al., Plasma Phys. Rep. 28, 12 (2002)] maximises intensity per unit energy for a given laser power. By scanning the target thickness and electron density, optimal conditions for $\gamma$-photon generation are identified. Additionally, we analyse the effect of laser polarisation (linear, radial and azimuthal) showing that radial polarisation yields superior performance due to a dominant longitudinal electric field component. The study is extended across a wide range of laser powers, revealing a scaling law for photon conversion efficiency. The resulting particle distributions are further used in Monte Carlo simulations [D. Kolenaty et al., Phys. Rev. Res. 4, 023124 (2012)] to model their interaction with high-Z targets, confirming additional pair production and radioactive nuclide generation via photonuclear reactions.
In [P. Hadjisolomou et al., Sci. Rep. 12, 17143 (2022)], we model the effect of a preplasma formed by a nanosecond pedestal, using a density profile obtained from magnetohydrodynamics simulations [I. Tsygvintsev and V. Gasilov, Math. Models Comput. Simul. 15, 623-629 (2023)]. Under irradiation by a $10 \, \mathrm{PW}$, few-cycle laser, this structured target leads to extremely efficient $\gamma$-photon production. The resulting $\gamma$-ray flash exhibits a characteristic double-lobe angular pattern, centred around $\pm 30^\circ$ in the laser polarization plane. Temporal analysis of the emission indicates that $\gamma$-photon generation follows the sub-cycle dynamics of the driving field, with clear correlation to the laser wavelength. These results are further used in an all-optical scheme [A. J. MacLeod, Phys. Rev. A 107, 012215 (2023)], where the generated $\gamma$-photons collide with a secondary laser pulse to trigger nonlinear Breit–Wheeler pair production.
