Tracking the motion of charges in a terahertz light field byfemtosecond X-ray diffraction
In condensed matter, light propagation near resonances isdescribed in terms of polaritons, electro-mechanical excitations in whichthe time-dependent electric field is coupled to the oscillation ofcharged masses. This description under pins our understanding of themacroscopic optical properties of solids, liquids and plasmas, as well asof their dispersion with frequency. In ferroelectric materials, terahertzradiation propagates by driving infrared-active lattice vibrations,resulting in phononpolariton waves. Electro-optic sampling withfemtosecond optical pulses can measure the time-dependent electricalpolarization, providing a phase-sensitive analogue to optical Ramanscattering. Here we use femtosecond time-resolved X-ray diffraction, aphase-sensitive analogue to inelastic X-ray scattering, to measure thecorresponding displacements of ions in ferroelectric lithium tantalate,LiTaO3. Amplitude and phase of all degrees of freedom in a light fieldare thus directly measured in the time domain. Notably, extension ofother X-ray techniques to the femtosecond timescale (for example,magnetic or anomalous scattering) would allow for studies in complexsystems, where electric fields couple to multiple degrees offreedom.
- Research Organization:
- COLLABORATION - U.Oxford/UK
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 920250
- Report Number(s):
- LBNL-60948; R&D Project: 505001; BnR: KC0202020; TRN: US200818%%1109
- Journal Information:
- Nature, Vol. 442; Related Information: Journal Publication Date: Aug. 10,2006
- Country of Publication:
- United States
- Language:
- English
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