High-Order Harmonic Generation by Relativistic Plasma Singularities: The Driving Laser Requirements

We discuss the new regime of high-order harmonic generation by relativistic -irradiance multi-terawatt femtosecond lasers focused onto gas jet targets [PRL, 108, 135004, 2012; NJP, 16, 093003, 2014]. The laser induces multi-stream relativistic plasma flow resulting in the formation of density singularities: structurally stable, oscillating electron spikes coherently emitting high-frequency radiation. Here we analyse the dependence of the harmonic yield on the focal spot quality and derive the required laser parameters for efficient harmonics generation. We show the status of the J-KAREN-P laser [IEEE J. Sel. Topics Quantum Electron., 21, 1601118, 2015] and report on the progress towards satisfying these requirements.