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 $L_{\mathrm{g}}$ 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 $a_0\approx 2.1$, where $a_0$ is the peak vector potential normalized by $m_{\mathrm{e}}c/e$ with the elementary charge $e$, the electron rest mass $m_{\mathrm{e}}$, and the vacuum light velocity $c$. For all driver pulses, we observe correlated relativistic SHHG and electron emission in the range $L_{\mathrm{g}}\in [\hat{I}»/25,\hat{I}»/5]$, with an optimum gradient scale length of $L_{\mathrm{g}}\approx \hat{I}»/10$.