  The lack of available table-top extreme ultraviolet (XUV) sources with high
enough fluxes and coherence properties have limited the availability of
nonlinear XUV and x-ray spectroscopies to free electron lasers (FEL). Here, we
demonstrate second harmonic generation (SHG) on a table-top XUV source for the
first time by observing SHG at the Ti M2,3-edge with a high harmonic seeded
soft x-ray laser (HHG-SXRL) [1,2]. Further, this experiment represents the
first SHG experiment in the XUV. First-principles electronic structure
calculations are used to confirm the surface specificity and resonant
enhancement of the SHG signal. The realization of XUV-SHG on a table-top source
with femtosecond temporal resolution opens up tremendous opportunities for the
study of element-specific dynamics in multi-component systems where surface,
interfacial, and bulk-phase asymmetries play a driving role in smaller-scale
labs as opposed to FELs.
