<p><strong>Figure 4.</strong> Same as figure <a href="http://iopscience.iop.org/0953-4075/46/16/164014/article#jpb463824f3" target="_blank">3</a> for the 2PDI of the argon 3p shell in the region of the Cooper minimum. Solid: sequential 2PDI via the fine-structure Ar<sup>+</sup> (3p<sup>5</sup> <sup>2</sup>P<sub>3/2</sub>) state; dashed: summed over the unresolved Ar<sup>+</sup> (3p<sup>5</sup> <sup>2</sup>P<sub>1/2, 3/2</sub>) fine structure states.</p> <p><strong>Abstract</strong></p> <p>As an extension to recent developments in the theory of non-dipole effects in nonlinear photoprocesses in the XUV/x-ray wavelength regime, the sequential two-photon double ionization of the 3p shell in atomic argon is studied theoretically and compared to similar processes in the 2p shell of neon. The calculations predict distinct non-dipole effects in the region of the Cooper minimum in argon at photon energies around 50 eV, where they are of similar importance as at photon energies of more than 500 eV. The non-dipole effects should therefore be clearly observable in experiments performed at the present x-ray free electron lasers.</p
