Time-resolved X-ray diffuse scattering from non-equilibrium phonons in solids

Intense, ultra-short laser pulses are currently used to study a wide range of coherent as well as incoherent excitations in solids. However, visible and infrared radiation can only probe a reduced fraction of the Brillouin zone near the zone center and hence do not provide direct information on shorter range interactions. With the availability of ultra-intense and ultra-short x-ray pulses as 4$^{th}$ generation x-ray free-electron lasers come online, time-resolved x-ray diffuse scattering has the potential to be the ultimate tool to study excitations and their decay channels throughout the Brillouin zone. Here we will present measurements of the generation and decay of incoherent phonons throughout the Brillouin zone in bulk semiconductors as well as single-shot measurements of ultrafast melting and recrystallization in bimuth. Finally, I will discuss some of the unique challenges these experiments present and how this is shaping potential future scientific directions at 4$^{th}$ generation sources.