X-ray Raman scattering: a building block for nonlinear spectroscopy.

Area of Science:

• Physics
• Chemistry
• Spectroscopy

Background:

• Ultrafast X-ray free-electron laser (XFEL) pulses offer new possibilities for observing electronic motion.
• Nonlinear X-ray spectroscopy, particularly stimulated electronic X-ray Raman scattering, is a promising technique.

Purpose of the Study:

• To review recent experimental achievements in nonlinear X-ray spectroscopy.
• To assess the challenges and future prospects for implementing nonlinear coherent X-ray Raman spectroscopy.

Main Methods:

• Proof-of-principle experiments using attosecond XFEL pulses.
• Observation of stimulated X-ray emission and scattering in atomic gases (soft X-ray regime).
• Application of stimulated hard X-ray emission spectroscopy to transition metal complexes.

Main Results:

• Demonstration of stimulated X-ray emission and scattering in atomic gases.
• Initial results from stimulated hard X-ray emission spectroscopy on transition metal complexes.
• Progress towards realizing nonlinear X-ray spectroscopy for studying ultrafast dynamics.

Conclusions:

• Experimental progress has been made in developing nonlinear X-ray spectroscopic techniques.
• Challenges remain in the full implementation of nonlinear coherent X-ray Raman spectroscopy.
• This work contributes to the measurement of ultrafast electronic and structural dynamics using X-rays.