Hard x-ray - optical four-wave mixing using a split-and-delay line.

Area of Science:

• Condensed matter physics
• Ultrafast science
• X-ray science

Background:

• Hard X-ray free-electron lasers (FELs) offer unprecedented temporal and spatial resolution.
• Nonlinear optical spectroscopy methods are being extended to hard X-ray photon energies.
• Understanding energy coupling in materials requires advanced spectroscopic techniques.

Purpose of the Study:

• To perform hard X-ray, optical four-wave mixing (4WM) measurements at 9.8 keV.
• To investigate the coherence properties of X-ray excitations and their coupling to material degrees of freedom.
• To establish experimental requirements for future nonlinear X-ray spectroscopy.

Main Methods:

• Utilized a split-and-delay line at the Linac Coherent Light Source (LCLS) for X-ray Correlation Spectroscopy (XCS).
• Created an X-ray transient grating (TG) using crossing X-ray beams.
• Diffracted 400 nm optical laser pulses from the X-ray TG and varied pulse delays.

Main Results:

• No coherent 4WM signal was observed in bismuth germinate (BGO), zinc oxide (ZnO), and yttrium aluminum garnet (YAG).
• X-ray pulse delay scans provided insights into material and light source coherence.
• Optical laser delay scans revealed X-ray induced lattice dynamics in the studied solids.

Conclusions:

• The absence of a coherent 4WM signal sets important parameters for future experiments.
• The study demonstrates the potential of nonlinear spectroscopy in the hard X-ray regime.
• This work is a significant step towards advancing time-resolved spectroscopy with hard X-rays.