Experimental and Theoretical Study of Four-Wave Mixing in Krypton

Nonlinear four-wave mixing processes resulting from the interaction of ultrashort extreme ultra violet pulse trains and strong infrared laser pulses are productive tools to examine the dynamics of electronic wavepackets in atomic and molecular systems, allowing for the probing of light induced coupling of excited states. In this study, this technique is used to observe quantum beats produced by a superposition of autoionizing electronic states. In addition, we propose a minimal semi empirical multichannel quantum defect theory model that effectively replicates the features observed in the experiment and provides a possible mechanism for their production. The study shows the interplay of multiple unassigned autoionizing states, and hints towards the possibility of interactions with doubly excited states, while at the same time opening the door for ab-initio calculations that can test the proposed theoretical findings.