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

The high-order harmonics generation (HHG) in an electron-positron-ion plasma with varying proportions is investigated. We find that the amplitude of HHG spectrum is enhanced in mixed targets compared with a pure electron-ion target. Several prominently amplified spectral features are observed in the spectrum, i.e., harmonics of the local plasma frequency in the inertial length region. This is due to the strong excited plasma oscillation driven by an energetic positron flow. The spectral features provide detailed information of the pair plasma properties in the target, thus serving as an in situ diagnostic of the pair plasmas generated in the experiments using intense lasers.