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Events on Monday, August 26th, 2024

Nonlinear X-ray Optics for Transition Metal Chemistry and Coherent X-ray Spectroscopy
Time: 10:00 am - 12:00 pm
Place: B343 Sterling Hall;
Speaker: Zain Abhari, Physics PhD Graduate Student
Abstract: My thesis work encompasses two main projects: building and commissioning an XUV femtosecond transient absorption spectroscopy tabletop instrument and designing new nonlinear spectroscopy and imaging techniques in the hard X-ray domain utilizing stimulated X-ray emission.

Advancements in tabletop XUV sources driven by high harmonic generation have enabled ultrafast, element-specific measurements outside large-scale X-ray free electron laser facilities. Despite their potential, these sources were previously limited to academic labs specializing in nonlinear optics and ultrafast laser systems. To increase access across other scientific disciplines, we established an XUV femtosecond absorption spectroscopy tabletop (XFAST) instrument at the University of Wisconsin – Madison as a national user facility. My contributions included constructing the vacuum system and configuring the optical pump line. In addition to being the instrumentation consultant for XFAST, I have a focus in designing nonlinear hard X-ray spectroscopy techniques and new X-ray sources.

Furthering our understanding of electron dynamics and obtaining structural information from materials necessitates ultrashort X-ray pulses on femtosecond or attosecond timescales. We pursue two methods to achieve intense, ultrafast X-ray pulses: stimulated emission for femtosecond coherent hard X-ray pulse pairs, and superradiance for hard X-ray attosecond spikes. Recently, we designed and demonstrated a femtosecond X-ray pulse pair spectrometer using stimulated emission, encoding ultrafast dynamics information in CCD image contrast. Superradiance, if observed in the hard X-ray regime, could offer powerful imaging capabilities, although distinguishing it from stimulated emission presents challenges. Our designed experiments aim to confirm superradiance's observation separately from stimulated emission.
Host: Uwe Bergmann
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