Evidence for Collective Nonlinear Interactions in X Ray into Ultraviolet Parametric Down-Conversion

Area of Science:

• Solid-state physics
• X-ray optics
• Quantum optics

Background:

• Parametric down-conversion (PDC) typically involves nonlinear optical processes.
• Understanding x-ray PDC is crucial for advanced material characterization.
• Existing models often focus on atomic or bond-level responses.

Purpose of the Study:

• Investigate nonmonotonic photon energy dependencies in x-ray to ultraviolet PDC.
• Explain observed count rate and rocking curve anomalies.
• Propose a new theoretical framework for x-ray PDC phenomena.

Main Methods:

• Experimental observation of x-ray parametric down-conversion.
• Analysis of photon count rates and rocking curves.
• Theoretical modeling incorporating collective phenomena.

Main Results:

• Observed peculiar nonmonotonic energy dependencies in x-ray PDC count rates and rocking curves.
• Standard atomic and bond charge models failed to explain the data.
• Discovered peaks in the energy spectrum attributed to nonlinear interactions with plasmons.

Conclusions:

• Collective phenomena, specifically nonlinear interactions with plasmons, play a significant role in x-ray PDC.
• The findings challenge existing models and highlight the limitations of purely atomic responses.
• Nonlinear x-ray interactions offer a novel method for probing collective effects at the atomic scale in solids.