Attosecond bunches of gamma photons and positrons generated in nanostructure targets.

The subatomic experimental exploration of physical processes on extremely short time scales has become possible by the generation of high-quality electron bunches and x-ray pulses with subfemtosecond durations. Increasing the photon energy from the x-ray to gamma-ray regime makes probing of extremely small space-time domains accessible. Here, a mechanism for generating attosecond gamma photon and positron bunches with small divergence using laser intensities below 10^{23}W/cm^{2} is proposed. In contrast with previous works, in our scheme a single laser pulse is sufficient instead of two counterpropagating pulses. Numerical simulations are used to formulate the conditions for confined radiation and to characterize the generated photon and positron bunches.