High-order harmonic generation in an electron-positron-ion plasma.

Area of Science:

• Plasma Physics
• Laser-Plasma Interactions
• High-Energy Density Physics

Background:

• Laser interaction with mixed plasmas is crucial for understanding high-order harmonic generation.
• Previous studies focused on idealized plasma conditions, lacking self-consistent pair production scenarios.

Purpose of the Study:

• Investigate high-order harmonic generation in electron-positron-ion plasmas.
• Analyze the impact of laser intensity and quantum electrodynamic effects on plasma dynamics and harmonic spectra.

Main Methods:

• Utilized particle-in-cell simulations to model laser-plasma interactions.
• Incorporated quantum electrodynamic effects, including photon emission and pair production.
• Studied both idealized and self-consistent scenarios of pair plasma creation.

Main Results:

• Observed well-defined harmonic signals in idealized plasmas due to inverse two-plasmon decay.
• Demonstrated signal detection at twice the plasma frequency for low pair densities (∼10⁻⁵).
• In self-consistent simulations, dense, hot pair plasmas were created with high laser absorption and enhanced high-frequency harmonics, but characteristic plasma frequency harmonics were absent due to plasma inhomogeneity.

Conclusions:

• Laser-driven pair production in plasmas leads to complex harmonic spectra.
• Plasma inhomogeneity significantly affects harmonic generation, suppressing characteristic signals while enhancing others.
• Quantum electrodynamic effects play a critical role in ultraintense laser interactions with matter.