Numerical Simulations of Nonstationary Non-radiating States of Laser-plasma

In this work, we present a model to study dynamical configurations of plasma created through the ionization of small gas targets by intense bichromatic femtosecond laser pulses. Strong time-dependent currents excited in this interaction lead to the emission of high-power terahertz waves. After the release of a short terahertz pulse, a nearly non-radiating plasma configuration is formed, even though the charge and current distributions remain time-dependent. It is known from classical electrodynamics that accelerated charged particles emit electromagnetic radiation. However, this statement may not be true if a continuous distribution modeling charges and currents in macroscopic systems is considered. In this case, time-dependent space-limited, non-radiating arrangements of charges and currents may exist 1, 2. In theory, the number of such configurations is large, but their practical realization was believed to be impossible for a long time. The experimental evidence of the toroidal multipoles 3, 4 allowing the construction of non-radiating states was observed recently while studying the optical properties of metamaterials 5. We examine the formation of non-radiating distributions in a plasma arising from the ionization of atomic gases by an intense laser pulse by means of particle-in-cell simulations.