Fig. 1. Intensity limits for ionization and the one-dimensional plasma expansion model from Samir et al. The dashed back line indicates a Gaussian pulse.

Fig. 2. Self-similar analytical solution to the one-dimensional plasma expansion. $n_{c}$: critical density

Fig. 3. Schematics of the low-ASE version of the PHELIX laser commissioned in 2012. The auxiliary compressor is used for temporal contrast characterization on a daily basis.

Fig. 4. ASE level at PHELIX as a function of the seed energy measured at the regenerative amplifier stage input.

Fig. 5. Measurement of the relative pulse energy as a function of the number of round trips in the regenerative amplifier. The part when $N\in [20\ldots 40]$ is used for the fit.

Fig. 6. Comparison of the single (blue) and double (dark green) plasma mirror effect to the plasma expansion threshold for gold (red) and hydrogen (blue).

Fig. 7. Plasma mirror reflectivity: data and fit based on an error function.