Gamma-ray generation in ultrahigh-intensity laser-foil interactions

Incoherent photon emission by ultrarelativistic electrons in the normal incidence of a laser pulse on a foil is investigated by means of three-dimensional numerical simulations in the range of intensities 2 × 10²¹ -- 2 × 10²⁵ W \, cm⁻² and electron densities 2 × 10²² -- 1 × 10²⁴ cm⁻³. We focus on properties of the resulting synchrotron radiation, such as its overall energy, directivity of the radiation pattern and slope of the energy spectrum. Regimes of laser-foil interactions are studied in the framework of a simple analytical model. The laser-plasma parameters for efficient gamma-ray generation are found and revealed to be close to the parameters for relativistic foil motion. It is shown that in the case of oblique incidence of a 3 PW, 10 fs laser pulse on a thin foil about 10⁸ photons/0.1% bandwidth are produced at the energy level of 1 MeV that significantly exceeds performance of the modern Compton gamma-ray sources. Various applications of the gamma-ray bunches are discussed.