Enhanced coherent transition radiation from midinfrared-laser-driven microplasmas

Area of Science:

• Plasma Physics
• Laser-Plasma Interactions
• Terahertz (THz) Science

Background:

• Ultrafast laser pulses interacting with plasmas generate terahertz (THz) radiation.
• Understanding the energy scaling of THz generation is crucial for applications.

Purpose of the Study:

• To investigate the energy scaling of THz radiation produced by ultrafast plasma currents driven by relativistic laser pulses.
• To elucidate the underlying physical mechanisms governing THz generation in different laser intensity regimes.

Main Methods:

• Particle-in-cell (PIC) simulations in 2D and 3D were employed.
• Analysis focused on the relationship between laser parameters (intensity I₀, wavelength λ₀) and THz output energy (W_THz).
• Electron distribution functions were analyzed to understand electron temperature (Tₑ) scaling.

Main Results:

• THz output energy (W_THz) scaling is complex and does not simply follow I₀λ₀.
• For moderate fields, W_THz scales as (I₀λ₀²)^α, indicating vacuum electron acceleration.
• For strong relativistic fields, W_THz scales with the ponderomotive potential, converging to W_THz ∝ I₀²/λ₀², indicating ponderomotive charge acceleration.
• Electron temperature (Tₑ) exhibits similar scaling behavior to W_THz.

Conclusions:

• The study provides a clear physical picture of THz generation in relativistic and subrelativistic laser plasmas.
• THz yield as a function of I₀ and λ₀ can serve as a probe for hot electron temperature (Tₑ).
• The exponent α of the (I₀λ₀²)^α fit can help identify dominant laser-to-electron energy conversion mechanisms.