The XUV pulse train generates a coherence of autoionizing Rydberg states of carbon dioxide spanning 17.3 -18.1 eV, including members of the Henning diffuse and Henning sharp series . This coherence is probed by two time-coincident, noncollinear NIR pulses, resulting in transient wave-mixing signals that emit at a spatial location distinct from the XUV harmonics dictated by wavevector phase matching conditions (Fig. ). For a FWM process requiring both NIR beams, the wave-mixing signals will emit at a divergence angle ( 𝜙 div ) described by the following expression :