Powerful laser-produced quasi-half-cycle THz pulses.

The Maxwell equations-based 3D-analytical solution for the terahertz (THz) half-cycle electromagnetic wave transition radiation pulse has been found. This solution describes generation and propagation of transition radiation into free space from laser-produced relativistic electron bunch which crosses a target-vacuum interface as a result of ultrashort laser pulse interaction with a thin high-conductivity target. The analytical solution found complements the theory of laser initiated transition radiation. It describes the THz wave half-cycle pulse at the arbitrary distance from a target surface including near-field zone rather than its standard far-field characterization. The analytical research has also been supplemented with the 3D simulations using the finite-difference time-domain method, which makes it possible for description of much wider spatial domain as compared to that from the particle-in-cell approach. The presented result sheds light fundamentally on the interference of the electron bunch field and the generated THz field of broadband transition radiation from laser-plasma interaction. The latter is studied for a long time in the experiments with solid density plasma and the theory developed may inspire to targeted measurements and investigations of unique super intense half-cycle THz radiation waves near the laser target.

Ultrafast target charging due to polarization triggered by laser-accelerated electrons.

A significant step has been made towards understanding the physics of the transient surface current triggered by ejected electrons during the interaction of a short intense laser pulse with a high-conductivity target. Unlike the commonly discussed hypothesis of neutralization current generation as a result of the fast loss of hot electrons to the vacuum, the proposed mechanism is associated with excitation of the fast current by electric polarization due to transition radiation triggered by ejected electrons. We present a corresponding theoretical model and compare it with two simulation models using the finite-difference time-domain and particle-in-cell methods. Distinctive features of the proposed theory are clearly manifested in both of these models.