Time-Resolved X-Ray Scattering from Coherent Excitations in Solids

Recent advances in pulsed x-ray sources have opened up new opportunities to study the dynamics of matter directly in the time domain with picosecond to femtosecond resolution. In this article, we present recent results from a variety of ultrafast sources on time-resolved x-ray scattering from elementary excitations in periodic solids. A few representative examples are given on folded acoustic phonons, coherent optical phonons, squeezed phonons, and polaritons excited by femtosecond lasers. Next-generation light sources, such as the x-ray-free electron laser, will lead to improvements in coherence, flux, and pulse duration. These experiments demonstrate potential opportunities for studying matter far from equilibrium on the fastest time scales and shortest distances that will be available in the coming years.