An investigation on THz yield from laser-produced solid density plasmas at relativistic laser intensities

Abstract

We experimentally characterize the generation of high-power terahertz radiation (THz) at the rear surface of a target irradiated by multiple laser pulses. A detailed dependence of the THz yield as a function of laser pulse duration, energy, target material and thickness is presented. We studied the THz radiation emitted mainly in two directions from the target rear surface, namely target normal (acceptance angle 0.87 sr) and non-collinear direction (perpendicular to the target normal directionacceptance angle 4.12 sr). Independent measurements based on electro-optic diagnostics and pyroelectric detector were employed to estimate the THz yield. Most of the energy is emitted at large angles relative to the target normal direction. THz yield increases with incident laser intensity and thinner targets are better emitters of THz radiation compared to thicker ones.

Multi-MV/cm longitudinally polarized terahertz pulses from laser–thin foil interaction

“…This agrees well with the behavior expected from the plasma expansion model, which phenomenologically describes the THz generation mechanism under intense laser-solid interaction [24]. It says that THz radiation is emitted by the charge particle acceleration process at the foil rear surface, and the polarization of the radiation is radial.…”

“…Further analysis also reveals that the detected THz pulse exhibits quasi-single-cycle waveform with temporal durations of approximately 220 fs and 600 fs for transverse (ε y ) and longitudinal (ε z ) polarizations, respectively. This difference in the detected temporal structure of the waveforms can be ascribed to the difference in the response function of the two crystals used here [24,28], clearly supported by the respective THz spectra shown in the inset of Fig. 3(a).…”

“…Interestingly, an asymmetric field pattern is visible between the left and right sides of the beam, which may be attributed to the presence of different THz generation processes. THz generation due to ponderomotively driven electrons in the laser propagation direction gives rise to the asymmetric THz emission pattern compared to the uniform dipolelike emission from the ion acceleration process [24].…”

“…Upon exiting, they create a charge separation field of the order of TV/m at the rear surface in the target normal direction [21]. This field is transient in nature and is responsible for the acceleration of the ions, which in turn results in a dipole-like THz emission [22][23][24][25].…”

Towards Terawatt-Scale Spectrally Tunable Terahertz Pulses via Relativistic Laser-Foil Interactions

“…Very recently, multimillijoule THz pulses have been demonstrated experimentally [31]. For the THz emissions from the rear side of a solid target [31][32][33][34][35][36][37][38][39][40], a number of studies have been reported on the influence of laser and target parameters on the THz radiation, and several distinct models have been proposed to understand the specific experimental observations. Nevertheless, the distinctions of these models and their respective contributions to the global THz radiation remain elusive, even under comparable laser conditions [32][33][34][35][36][37][38][39][40].…”