Unified ab initio treatment of attosecond photoionization and Compton scattering

We present a new theoretical approach to attosecond laser-assisted photoand Compton ionization. Attosecond x-ray absorption and scattering are described by Ŝ (1,2)-matrices, which are coherent superpositions of ‘monochromatic’ Ŝ(1,2)-matrices in a laser-modified Furry representation. Besides refining the existing theory of the soft x-ray photoelectron attosecond streak camera and spectral phase interferometry (ASC and ASPI), we formulate a theory of hard x-ray photoelectron and Compton ASC and ASPI. The resulting scheme has a simple structure and leads to closed-form expressions for ionization amplitudes. We investigate Compton electron interference in the separable Coulomb–Volkov continuum with both Coulomb and laser fields treated non-perturbatively. We find that at laser-field intensities below 1013 Wcm−2 normalized Compton lines almost coincide with the lines obtained in the laser-free regime. At higher intensities, attosecond interferences survive integration over electron momenta, and feature prominently in the Compton lines themselves. We define a regime where the electron ground-state density can be measured with controllable accuracy in an attosecond time interval. The new theory provides a firm basis for extracting photoand Compton electron phases and atomic and molecular wavefunctions from experimental data. S This article has associated online supplementary files for Fortran implementation of differential Compton electron spectra and Compton lines (Some figures in this article are in colour only in the electronic version)