Figure 2
From: Stable femtosecond X-rays with tunable polarization from a laser-driven accelerator
X-ray profiles for different gas compositions. (a) Angular profile of the X-ray beam for four consecutive shots in pure helium and in the gas mixture (He+1% N2). The color scale is the same for all images. (b) Integrated signal with the same area as in a for 50 consecutive shots in the mixed gas. Each green dot represents the centroid position for a single shot of the series. The standard deviation is 1 mrad, which corresponds to ~10% of the beam FWHM divergence. The FWHM divergences are 33 and 12 mrad along the two axes of the ellipse.
