What is the fine-grained topic of the following text: Researchers have succeeded in using the immensely powerful x-ray pulses from the free electron laser (XFEL) facility SACLA to investigate excited-state induced transient lattice dynamics on sub-picosecond time scales in phase-change materials via x-ray diffraction. Only return the topic.
Investigating transient lattice dynamics in phase-change materials using x-ray diffraction from XFEL facility SACLA.