Fig. 3: Measurement of variable polarisation for soft X-rays at 700 eV.

The plots show the recoil ion momentum distribution of He+ ions projected onto the plane of the X-ray propagation direction with (a) linear horizontal (LH), (b) linear vertical (LV), and (c) circular polarised (CP) radiation. The arrows indicate the polarisation direction. The radius of the distribution corresponds to the absolute momentum of 7 a.u. (atomic units) imparted by the photoelectron onto the recoil ion.