  Dark field X-ray microscopy (DXFM) has enabled experiments to visualize
microstructural distortions in bulk crystals. Using the femtosecond X-ray
pulses generated by X-ray free-electron lasers (XFEL), DFXM can achieve ~1-um
spatial resolution and <100 fs time resolution simultaneously. In this paper,
we present the first ultrafast DFXM measurements at the European XFEL. In this
work, we demonstrate DFXM of laser-induced phonon wavepackets propagating
through dislocations inside a diamond single crystal. In addition to
demonstrating this new capability, we present two new DFXM scanning techniques
for XFEL applications, 3D and axial-strain scans with sub-{\mu}m spatial
resolution. With this progress to XFEL DFXM, we discuss new opportunities to
study multi-timescale spatio-temporal dynamics of defects, strain waves, and
other localized phenomena deep inside crystals.
