X-ray vacuum diffraction at finite spatiotemporal offset

We study the nonlinear QED signature of x-ray vacuum diffraction in head-on collision optical high-intensity and free-electron laser pulses at finite spatiotemporal offsets between foci. The driven scattering signal photons outside forward cone probe constitutes a prospective experimental quantum nonlinearity. Resorting to simplified phenomenological ad hoc model, it was recently argued that angular distribution far-field is sensitive wavefront curvature beam interaction region with pump. In this work, we model both pump fields as pulsed paraxial Gaussian beams reanalyze effect from first principles. focus on an individual nonlinearity potential means improve signal-to-background separation birefringence experiments.