Role of resonance absorption in terahertz radiation generation from solid targets

Modeling terahertz emission from the target rear side during intense laser-solid interactions

Relativistic laser-solid target interaction is a powerful source of terahertz radiation where broadband terahertz radiation is emitted from the front and rear surfaces of the target. Even though several experimental works have reported the generation of subpicosecond duration gigawatt peak power terahertz pulses from the target rear surface, the underlying physical process behind their origin is still an open question. Here we discuss a numerical model that can accurately reproduce several aspects of the experimental results. The model is based on the charged particle dynamics at the target rear surface and the evolution of the charge separation field. We identify the major contributors that are responsible for broadband terahertz emission from the rear surface of the target.

Sub GV/cm terahertz radiation from relativistic laser-solid interactions via coherent transition radiation

Broadband terahertz (THz) radiation with extremely high peak power, generated by the interaction of a femtosecond laser with a thin solid target, has been investigated via particle-in-cell simulations. The spatial (angular) and temporal profiles of the THz radiation reveal that it is caused by the coherent transition radiation emitted when laser-produced hot electrons pass through the front or rear surface of the target. Dependence of the THz radiation on laser and target parameters is studied; it is shown to have a strong correlation with hot electron production. The THz radiation conversion efficiency can be as high as a few times 10^{-3}. This radiation is not only a potentially high power THz source, but may also be used as a unique diagnostic of hot electron generation and transport in relativistic laser-solid interactions.

Backward terahertz radiation from intense laser-solid interactions

We report a systematic study on backward terahertz (THz) radiation generation from laser-solid interactions by changing a variety of laser/plasma parameters. We demonstrate a high-energy (with an energy flux density reaching 80 μJ/sr), broadband (>10 THz) plasma-based radiation source. The radiation energy is mainly distributed either in the >10 THz or <3 THz regions. A radial surface current formed by the lateral transport of low-energy electrons (LEE) is believed to be responsible for the radiation in the high-THz region (>10 THz), while high-energy surface fast electrons (SFE) accelerated along the target surface mainly contribute to lower frequency (<3 THz) radiation. The unifying explanation could be applied to backward THz radiation generation from solid targets with presence of relative small preplasmas.