Towards novel probes for valence charges <i>via</i> X-ray optical wave mixing

We present a combined theoretical and experimental study of X-ray optical wave mixing. This class nonlinear phenomena combines the strengths spectroscopic techniques from domain, with high-resolution capabilities X-rays. In particular, sensitivity these can be exploited to selectively probe valence dynamics. Specifically, we focus on effect parametric down-conversion. description process, which deduce observable response charges. Subsequently, simulate scattering patterns for realistic conditions identify characteristic signatures conversion. For observation this signature, dedicated setup results detailed investigation. However, do not find evidence effect. finding stands in strong contradiction previous claims proof-of-principle demonstrations. Nevertheless, are optimistic employ related mixing processes basis methods presented here probing dynamics future.