#  Ultrafast X-Rays  

 



   ![RIXS process](/sites/g/files/omnuum1256/files/styles/hwp_1_1__720x720_scale/public/2024-12/Fig1_trRIXS_technique.jpg?itok=LkfjpQKd) 

 

   ![LCLS beamline](/sites/g/files/omnuum1256/files/styles/hwp_1_1__720x720_scale/public/2024-12/LCLSXFELm.jpg?itok=7N_BFuAO) 

 

LCLS XFEL Undulator Hall. [Image credit](https://www.flickr.com/photos/slaclab/22331906503/in/album-72157624840675621). Non-equilibrium states in light-driven quantum materials arise from microscopic processes that require interrogating finite-momentum dynamics on ultrafast timescales. To address this challenge, our group employs a suite of ultrafast X-ray scattering techniques, including time-resolved X-ray diffraction (tr-XRD), resonant soft X-ray scattering (tr-RSXS), X-ray absorption spectroscopy (tr-XAS), and resonant inelastic X-ray scattering (tr-RIXS). tr-XRD and tr-RSXS provide incisive insights into structural and electronic ordering, capturing lattice distortions induced by optical phonon excitation and the dynamics of ordered electronic and spin states. tr-XAS measures the unoccupied density of states in light-driven quantum materials via direct X-ray photon absorption. tr-RIXS, an emerging spectroscopic technique, probes valence-band excitations—such as phonons, spin waves, orbital transitions, and plasmons—through momentum- and energy-resolved detection of scattered photons. Utilizing femtosecond X-ray pulses from free-electron lasers, this combination of techniques offers unparalleled access to the microscopic physics of nonequilibrium photoexcited states. Our group routinely performs experiments at leading X-ray free-electron laser facilities worldwide— including the LCLS in the US, the European XFEL in Germany, SwissFEL in Switzerland, and PAL-XFEL in South Korea.



 

###  Reviews: 

- **M. Mitrano**, S. Johnston, Y.-J. Kim, & M. P. M. Dean (2024): Exploring Quantum Materials with Resonant Inelastic X-Ray Scattering, [*Phys. Rev. X* **14**, 040501.](https://journals.aps.org/prx/abstract/10.1103/PhysRevX.14.040501)
- **M. Mitrano,** & Y. Wang (2020): Probing light-driven quantum materials with ultrafast resonant inelastic X-ray scattering. [*Communications Physics* **3**, 184.](https://www.nature.com/articles/s42005-020-00447-6)