We are interested in development of new spectroscopic capabilities based on nonlinear optics, ultrafast pulses of coherent radiation and ultrashort electron pulses. A topic of particular focus is the method of terahertz (THz) time-domain spectroscopy. In this technique, ultrafast visible laser pulses are converted into single cycles of radiation in the THz part of the electromagnetic spectrum by means of phase-matched optical rectification in suitable nonlinear materials. The resulting electric-field waveform is detected by electro-optic sampling using timesynchronized visible laser pulses. In addition to many applications of this method for time-resolved spectroscopy of nanoscale materials, we have contributed to development of different aspects of the THz source and the electro-optic detection scheme. At the opposite end of the electromagnetic spectrum from THz radiation, we are seeking unique applications of coherent pulsed x-ray radiation from the LCLS light source at SLAC to probe ultrafast dynamics at surfaces and in nanoscale materials. We are also involved in employing pump-probe schemes with ultrashort electron pulses to study structural dynamics and phase transitions of atomically thin materials.
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