Capturing Atomic Scale Dynamics with Pulsed x-ray Sources

The availability of a “pulsed” x-ray source enables time-resolved measurements on versatile choices of materials via a repetitive pump-probe approach and speckle visibility analysis. In my first half of the talk, I would like to demonstrate versatile uses of a pump-probe based x-ray scattering method, better known as time-resolved x-ray diffraction [TRXD], for studying impulsive responses of bulk and heterostructure semiconductors upon femtosecond laser excitation. At 3rd generation light sources such as Pohang Light Source where the tunability over large x-ray energy range and delivery of high photon flux are possible, the TRXD methods allow us to access sub-angstrom spatial and sub-nanosecond temporal resolutions. In latter part of the talk, I would like present capabilities of hard x-ray free electron lasers [XFEL] whose underlying emission principle is quite different from tabletop optical lasers. In particular, the XFEL sources such as the Linac Coherent Light Source at SLAC deliver femtosecond hard x-ray pulses that are considered transversely fully coherent. Subsequently, I will elaborate on feasibilities of studying structures and dynamics in an amorphous system at atomic length and time scales at XFEL facilities.