High-Harmonic Generation and Correlated Electron Emission from Relativistic Plasma Mirrors at 1 kHz Repetition Rate

Abstract

We report evidence for the first generation of XUV spectra from relativistic surface high-harmonic generation (SHHG) on plasma mirrors at a kilohertz repetition rate, emitted simultaneously with energetic electrons. SHHG spectra and electron angular distributions are measured as a function of the experimentally controlled plasma density gradient scale length L g for three increasingly short and intense driving pulses: 24 fs and a 0 = 1.1 , 8 fs and a 0 = 1.6 , and finally 4 fs and a 0 ≈ 2.1 , where a 0 is the peak vector potential normalized by m e c / e with the elementary charge e , the electron rest mass m e , and the vacuum light velocity c . For all driver pulses, we observe correlated relativistic SHHG and electron emission in the range L g ∈ λ / 20 , λ / 4 , with an optimum gradient scale length of L g ≈ λ / 10 . This universal optimal L g -range is rationalized by deriving a direct intensity-independent link between the scale length L g and an effective similarity parameter for relativistic laser-plasma interactions.