A. Cavalleri1,2, S. Wall1, C. Simpson1, E. Statz3, D. W. Ward3, K. A. Nelson3, M. Rini4 and R. W. Schoenlein4
In condensed matter, light propagation near resonances is described in terms of polaritons, electro-mechanical excitations in which the time-dependent electric field is coupled to the oscillation of charged masses1,2. This description underpins our understanding of the macroscopic optical properties of solids, liquids and plasmas, as well as of their dispersion with frequency. In ferroelectric materials, terahertz radiation propagates by driving infrared-active lattice vibrations, resulting in phonon-polariton waves. Electro-optic sampling with femtosecond optical pulses3,4,5 can measure the time-dependent electrical polarization, providing a phase-sensitive analogue to optical Raman scattering6,7. Here we use femtosecond time-resolved X-ray diffraction8,9,10, a phase-sensitive analogue to inelastic X-ray scattering11,12,13, to measure the corresponding displacements of ions in ferroelectric lithium tantalate, LiTaO3. Amplitude and phase of all degrees of freedom in a light field are thus directly measured in the time domain. Notably, extension of other X-ray techniques to the femtosecond timescale (for example, magnetic or anomalous scattering) would allow for studies in complex systems, where electric fields couple to multiple degrees of freedom14.
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, UK
- Central Laser Facility & Diamond Light Source, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
Correspondence to: A. Cavalleri1,2 Correspondence and requests for materials should be addressed to A.C. (Email: a.cavalleri1@physics.ox.ac.uk).
Received 1 May 2006 |Accepted 30 June 2006
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