Simulation of ultrafast electron diffraction intensity under coherent acoustic phonons

Area of Science:

• Materials Science
• Solid-State Physics
• Physical Chemistry

Background:

• Ultrafast electron diffraction (UED) is sensitive to crystal structure.
• Analyzing coherent acoustic phonons using UED is challenging due to complex diffraction intensity behavior, especially for higher harmonics.

Purpose of the Study:

• To theoretically analyze the effects of photoinduced coherent transverse and longitudinal acoustic phonons on electron diffraction.
• To provide a guide for the exploitation and modulation of coherent phonons.

Main Methods:

• Theoretical analysis of electron diffraction patterns.
• Simulation of UED in 30-nm films with varying optical penetration depths.
• Solving the wave equation to obtain atomic displacements.

Main Results:

• Complex relationship observed between phonon frequencies and diffraction signals.
• Results depend significantly on laser penetration depth, sample thickness, and temporal stress distribution.
• An intensity decomposition method was proposed to address in-phase oscillations and high harmonics from inhomogeneous excitation.

Conclusions:

• The study offers new perspectives for understanding lattice response under coherent phonons.
• Provides a framework for accurate analysis and modulation of coherent phonon signals in materials.