Laser-triggered terahertz emission from near-critical-density targets

Area of Science:

• Plasma Physics
• Laser-Plasma Interactions
• Terahertz Science

Background:

• Femtosecond laser pulses interacting with plasma can accelerate electrons.
• Terahertz (THz) radiation generation is crucial for various applications.
• Relativistic self-trapping (RST) is a regime of laser-plasma interaction.

Purpose of the Study:

• To investigate the generation of coherent transition radiation in the terahertz range using femtosecond laser pulses in a relativistic self-trapping regime.
• To maximize the total charge of accelerating electrons and the laser-to-electrons conversion rate.
• To compare the RST regime with standard laser-plasma targets for THz pulse generation.

Main Methods:

• Three-dimensional particle-in-cell simulations were employed.
• Simulations modeled femtosecond laser pulse propagation in near-critical density plasma.
• Electron escape dynamics from targets (low-density or thin foil) were analyzed.

Main Results:

• The RST regime significantly enhances electron acceleration and laser-to-electron conversion.
• Quasi-unipolar terahertz pulses with energies exceeding 100 mJ were generated from a 2-J laser pulse with optimized laser-target matching.
• The RST regime showed advantages over standard foil targets with preplasma for THz generation.

Conclusions:

• Femtosecond laser pulse propagation in the RST regime is highly effective for generating high-energy terahertz radiation.
• Optimized laser-target configurations in the RST regime enable efficient terahertz pulse production.
• The RST approach offers a superior method for terahertz generation compared to conventional techniques.