A multi-wave mixing study investigating electronic coupling of dark and continuum states in Neon.

Ultrafast non-linear mixing techniques have been recently extended to the extreme-ultraviolet (XUV) regime which made it possible to probe quantum states and their light-induced couplings. Using transient absorption spectroscopy, we observe electronic couplings between the Rydberg and continuum states around the ionization potential of neutral Neon, as well as couplings to the dark states of Neon involving four and six wave mixing processes. Moreover, we observe long-lived coherent beats involving the spin-orbit split dark states, which form interfering pathways in the multi-wave mixing processes. The photon energy tunability and time-delay of the near-infrared (NIR) probe pulse are used to control the contributions of the different pathways and investigate the electronic structure of the excited states of the atom. The strength of various four- and six-wave mixing signals show an interesting and counter intuitive behavior, which is being investigated.