In a high-power laser beam interaction with matter, a significant part of the incoming laser energy is transformed into transient electromagnetic pulses (EMPs) in the range of radio and microwaves as well as terahertz bands.

Emission in the frequency range lower than 30–100 GHz is usually produced on a timescale longer than 30–100 ps and in the case of the solid targets, is related to the relaxation of the charge accumulated during the laser pulse interaction. These electromagnetic fields can reach high intensities and can potentially represent a significant danger for the electronic devices placed in the vicinity of the interaction point, and can represent a serious limitation different experimental devices functionality.. Thus, the comprehension of the origin of these electromagnetic fields and their distribution is of primary importance for the safe operation of high-power and high-energy laser facilities, but also for the possible use of these high fields in several promising applications. A recognized main source of EMPs is the (solid) target positive charging caused by the fast-electron emission due to laser–plasma interactions. The fast charging induces high neutralization currents from the conductive walls of the vacuum chamber through the target holder. However, other mechanisms related to the laser–target interaction are also capable of generating intense electromagnetic fields. The correlation between EMP and accelerated particles parameters supported by simplified theoretical models could be used for a real-time evaluation of the accelerated particles as well as system parameters.

THz
One particular approach in probing radiation in the THz domain was by implementing at the TEWALAS facility several research studies that were focused on generating intense THz pulses by two-colour femtosecond filamentation in air and subsequent characterization of the main parameters obtained in terms of energy and waveforms using Terahertz time domain spectroscopy (THz-TDS) based on pump-probe signal reconstruction using an optically correlated femtosecond optical pulse into electro-optical crystals such as Zinc-Tellur (Zn-Te). Following these studies, the probing of the strong THz radiation emitted in the laser acceleration processes using electro-optic sampling in a single-shot regime is an ongoing research activity at CETAL-PW, focused on developing new experimental methods to be efficiently applied to the actual laser-plasma acceleration architecture in evaluating the properties of the resulting relativistic particles by single-shot electro-optic methods.