Experimental data
TIME-RESOLVED DARK-FIELD X-RAY MICROSCOPY
By combining pump–probe excitation with DFXM imaging of symmetry-breaking strain fields in the bulk, we visualize defect-mediated dynamics in Ge.DFXM experimental data and static · dynamic simulations support the observed contrast evolution and mode-conversion signatures.High X-ray penetration enables these dynamics to be imaged not only at the surface but throughout the bulk.
EXPERIMENTAL DATA & SIMULATIONS
This movie summarizes the full time-resolved DFXM measurement sequence. Periodic intact-state measurements were interleaved with the pump–probe delay scans to verify reversible sample recovery and measurement reproducibility.
Blue arrows indicate the longitudinal strain wave propagating along the depth direction, while red arrows indicate the transverse elastic wave propagating in plane.
A larger beam size enables a broader sample region to be probed. Consistent longitudinal and transverse wave responses are also observed near the dislocation on the right; the red arrows specifically mark the transverse in-plane component.
The same in-plane transverse strain-wave response is observed at a weak-contrast dislocation from 1,000 to 6,000 ps. The red arrow marks its propagation.
A simplified COMSOL model with an idealized defect geometry shows that rapid thermoelastic expansion following normal-incidence laser excitation launches a longitudinal strain wave into the depth of the crystal.
The interaction between the wave and the dislocation induces mode conversion into an in-plane transverse component, visible as two linear wave fronts propagating in opposite directions.
Shown quantity: depth-direction displacement; therefore, the incident longitudinal wave is also visible in the XY plane.
SUPPLEMENTARY MATERIAL
Static and dynamic simulations supporting the observed DFXM contrast and strain-wave dynamics.
The figure compares different dislocation types with their corresponding DFXM difference images. In our experimental geometry, the contrast and morphology observed in DFXM depend on the dislocation type and orientation.
To illustrate the DFXM signature of strain-wave propagation, a localized strain field was translated laterally and inward; the resulting contrast shifts are consistent with geometric predictions and do not imply physical defect motion.
COMSOL two-temperature-model simulation of ultrafast laser excitation in germanium, showing rapid electron heating followed by electron–phonon energy transfer to the lattice.
Stacked DFXM profiles show the emergence of an in-plane transverse component as the out-of-plane longitudinal strain wave interacts with a defect.