Acoustic pulse echoes probed with time-resolved X-ray triple-crystal diffractometry.

Area of Science:

• Physics
• Materials Science
• Acoustics

Background:

• Femtosecond laser irradiation can induce stress and generate acoustic waves in materials.
• Understanding acoustic wave propagation is crucial for material characterization and device performance.

Purpose of the Study:

• To detect and analyze acoustic pulse echoes generated by femtosecond laser irradiation.
• To investigate the time-dependent strain component and waveform evolution of acoustic pulses.
• To study the influence of initial stress and propagation on wave front distortion.

Main Methods:

• Utilized time-resolved x-ray triple-crystal diffractometry to detect acoustic pulse echoes.
• Irradiated silicon and gallium arsenide plates with femtosecond lasers.
• Analyzed the time-dependent longitudinal strain component of the propagating acoustic pulses.

Main Results:

• The polarity of the strain pulse depended on the optically induced initial stress.
• Bipolar pulse waveforms deformed and broadened during propagation.
• Observed three-dimensional wave front distortion, manifesting as pulse duration broadening.
• Wavefront distortion was consistent with boundary roughness in unpolished plates.

Conclusions:

• Acoustic pulse echo characteristics are sensitive to initial stress conditions.
• Wave propagation leads to gradual deformation and broadening of acoustic pulses.
• Surface roughness significantly impacts acoustic wave propagation and wavefront distortion.