Description
Petawatt-class (PW) laser systems can nowadays deliver 10 fs long optical pulses with intensities exceeding 10$^{20}$ W.cm$^{−2}$. When such ultraintense laser pulses interact with a solid metallic wire, electrons accelerated by the ponderomotive force reach relativistic energies, resulting in the emission of low-frequency electromagnetic radiation in the gigahertz (GHz) to terahertz (THz) range [1]. The THz radiation from laser-wire interactions can attain mJ energies with percent-level conversion efficiencies [2] and is frequency tunable through adjustment of the wire length. As this low-frequency emission can cause damage to electronic components [3] in the experimental chambers of PW laser facilities, a detailed understanding and control of the underlying radiation mechanisms in relativistic laser–solid interactions is required [4]. While Particle-In-Cell (PIC) simulations are widely used to investigate electromagnetic field generation by ultraintense laser-driven plasmas [1], a unified analytical framework capable of describing the full spectrum of emitted THz radiation is still lacking, in particular for laser-wire interactions.
In this work, we aim to develop an analytical model that describes the dominant laser-driven THz emission mechanisms to support the interpretation of both numerical and experimental results. We focus on low-frequency antenna radiation [5] and coherent transition radiation [6], accounting for diffraction effects induced by the finite wire size on the resulting spectra and angular distributions. We show that relatively simple analytical models can accurately reproduce THz emission features observed in PIC simulations of relativistic laser–wire interactions. While diffraction effects on antenna radiation remain negligible for laser-induced currents propagating along the surface of a thin wire [7], the coherence properties of transition radiation are strongly influenced by the self-field of the relativistic electron bunch crossing the thin wire plasma–vacuum interface [8]. Precise modeling of these mechanisms is therefore essential for optimizing laser-driven THz sources and advancing applications in strong-field THz science [9].