Fig. 6.

Scaling of charge within FWHM with laser power. Circles represent measured data points taken with a nitrogen doping of 1% at a plasma density of 3.1 × 10¹⁸ cm⁻³. The error bars represent the s.e.m. The red curve represents a fit following the expected $Q\propto \sqrt{\mathrm{P}}$ dependency. The relative energy spread measured to be ∼15% for all measurement points