Abstract
A novel scheme for generating powerful terahertz (THz) radiation based on laser-solid interactions is proposed. When a $p$-polarized femtosecond laser impinges obliquely on a plane solid target and the target partially blocks the laser energy, surface electrons are extracted out and accelerated by the laser fields, forming a low-divergence electron beam. A half-cycle THz radiation pulse is emitted simultaneously as the beam passes by the edge of the target, due to coherent diffraction radiation. Our particle-in-cell simulations show that the relativistic THz pulse can have an energy of a few tens of millijoule and the conversion efficiency can be over 1$\%$ with existing $\sim$J level femtosecond laser sources.
Highlights
Powerful terahertz radiation sources have attracted considerable attention due to their applications in many fields of science [1,2,3], such as THz spectroscopy of condensed matter or biological issues [4,5,6], nonlinear THz optics [7], and resonant control of materials [8,9]
When a pump laser impinges obliquely on a solid foil, and the target partially blocks the laser, as only the edge of the foil interacts with the laser pulse, well-collimated surface electrons are produced similar to those generated in nanostructured plasmas
It is not a typical coherent transition radiation (CTR), since the properties of the particle beam are dramatically modified by vacuum laser acceleration (VLA) in the vicinity of the target; thereby the dynamics following the transmission through the plasma-vacuum interface has a profound impact on the radiation field
Summary
Powerful terahertz radiation sources have attracted considerable attention due to their applications in many fields of science [1,2,3], such as THz spectroscopy of condensed matter or biological issues [4,5,6], nonlinear THz optics [7], and resonant control of materials [8,9]. When a pump laser impinges obliquely on a solid foil, and the target partially blocks the laser, as only the edge of the foil interacts with the laser pulse, well-collimated surface electrons are produced similar to those generated in nanostructured plasmas When such an electron beam is accelerated away from the target, it produces a CTR-like radiation due to the optical inhomogeneities in space. The radiation is coherent for wavelength longer than the duration of the electron beam, and radiated power greatly benefits from a small beam divergence It is not a typical CTR, since the properties of the particle beam are dramatically modified by VLA in the vicinity of the target (within the formation length [20] of CTR); thereby the dynamics following the transmission through the plasma-vacuum interface has a profound impact on the radiation field. Due to the complexity of the problem, fully kinetic particle-in-cell (PIC) simulations are employed to study the radiation properties and the electron dynamics
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