Speaker
Description
Nonlinear spectroscopy in the XUV and soft-X-ray regions offers a unique route to combine the symmetry sensitivity of optical nonlinear processes with the element and orbital selectivity of core-level resonances. We present an experimental platform for time-resolved XUV-to-soft-X-ray nonlinear spectroscopy at FEL sources, using second-harmonic generation as a representative nonlinear probe. The platform integrates tight beam focusing, optical-pump/XUV-probe synchronization, polarization-resolved detection, and shot-to-shot normalization for weak nonlinear signals. We discuss key experimental requirements, including photon density, focus stability, pulse-to-pulse fluctuations, detector sensitivity, sample damage, and discrimination of sample-generated second-harmonic photons from source harmonic background. Our current XUV-region implementation provides a practical basis for extending the methodology toward soft-X-ray FEL operation and applications to ultrafast interfacial, semiconductor, ferroelectric, and magnetic dynamics.
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