High efficiency and collimated terahertz pulse from ultra-short intense laser and cone target

Amplification of a terahertz wave via stimulated Raman scattering

Extremely strong terahertz (THz) waves are desperately demanded for investigating nonlinear physics, spectroscopy, and imaging in the THz range. However, traditional crystal-/semiconductor-based THz sources have limitations of reaching extremely high amplitude due to the damage threshold of devices. Here, by introducing Raman amplification to the THz range, we propose a novel, to the best of our knowledge, scheme to amplify THz waves in plasma. A long-pulse CO₂ pump laser transfers its energy to a multicycle, 10-THz seed in a two-step plasma. By one-dimensional simulations, a 0.87-GV/m, 1.2-ps-duration THz seed is amplified to 10 GV/m in a 5.7-mm-long plasma with an amplification efficiency approaching 1%. The method provides a new technology to manipulate the intensity of THz waves.

Highly efficient harmonic vortex generation from a laser irradiated hollow-cone target

It has been recently reported that ultraviolet harmonic vortices can be produced when a high-power circular-polarized laser pulse travels through a micro-scale waveguide. However, the harmonic generation quenches typically after a few tens of microns of propagation, due to the buildup of electrostatic potential that suppresses the amplitude of the surface wave. Here we propose to use a hollow-cone channel to overcome this obstacle. When traveling in a cone target, the laser intensity at the entrance is relatively low to avoid extracting too many electrons, while the slow focusing by the cone channel subsequently counters the established electrostatic potential, allowing the surface wave to maintain a high amplitude for a much longer distance. According to three-dimensional particle-in-cell simulations, the harmonic vortices can be produced with very high efficiency >20%. The proposed scheme paves the way for the development of powerful optical vortices sources in the extreme ultraviolet regime-an area of significant fundamental and applied physics potential.

Simulation Study of a Bright Attosecond γ-ray Source Generation by Irradiating an Intense Laser on a Cone Target

The interaction between an ultrastrong laser and a cone-like target is an efficient approach to generate high-power radiations such as attosecond pulses and terahertz waves. The objective is to study the γ-ray generation under this configuration with the help of 2D particle-in-cell simulations. It is deciphered that electrons experience three stages, including injection, acceleration and scattering, to emit high-energy photons via nonlinear Compton scattering (NCS). These spatial-separated attosecond γ-ray pulses own high peak brilliance (>1022 photons/(s·mm2·mrad2·0.1%BW)) and high energy (6 MeV) under the case of normalized laser intensity a0=30(I=2×1021 W/cm2). In addition, the cone target turns out to be an order of magnitude more efficient in energy transfer compared to a planar one.