Circular dichroism in XUV plus IR multiphoton ionization of atoms

Circular dichroism (CD) is theoretically considered for two-colour multiphoton ionization of arbitrary atomic subshells. In particular, p-subshell ionization is analysed and compared with s-subshell ionization. Simple analytical expressions for the CD are obtained for both s- and p-subshell ionization. The calculations performed for Ne(2p) ionization by an extreme ultraviolet pulse in the presence of an infrared laser pulse show that the CD in this case is appreciably larger than in previously discussed s-shell ionization. It makes this case favourable for applications as a sensitive tool for measuring the helicity of short-wavelength free-electron laser beams.