Fig. 2: Correlation of maximum wavelength and scale length.

Maximum wavelength of the reflected spectrum extracted from the 2-D PIC simulations for different preplasma scale lengths and maximum laser intensities (colored shapes). The uncertainties are given by the peak-to-valley difference between the maximum wavelength at 1 and 10% of the maximum spectral intensity. The colored dashed lines represent the maximum wavelength that has been calculated from the maximum holeboring velocity with equation (2), which is corrected by the initial shift of the preplasma expansion (black line). The initial maximum wavelength of the incoming laser pulse is given by \({\lambda }_{\max }=1061\) nm.