High wavevector optical phonons in microstructured Bismuth films.

We report the generation of high wavevector, large amplitude coherent optical phonons in a microstructured Bismuth film. A femtosecond laser pulse optically excites a periodic micron scale grating etched into a Bismuth film. The ultrafast excitation produced coherent optical phonon oscillations with wavevectors as large as 1 microm(-1), providing a possible method of generating an efficient sub-picosecond switch for hard x-rays.

Single-shot two-dimensional infrared spectroscopy.

Multidimensional infrared spectroscopy is a robust tool for studying the structural dynamics of molecules. In particular, twodimensional infrared (2DIR) spectroscopy can reveal vibrational coupling among the internal modes of molecules, uncovering the transient structure of complex systems. While spectroscopically very powerful, current experimental techniques are time consuming to perform, requiring ~10(6) laser shots for a single 2DIR spectrum. In this work, we demonstrate a new technique that can acquire a full 2DIR correlation spectrum using a single ultrafast laser pulse. This apparatus will allow 2DIR spectroscopy to be extended to systems that were unattainable with previous technology, including, irreversible chemical reactions, rapid flow experiments, or with low repetition rate laser systems.

Half-cycle-pulse terahertz emission from an ultrafast laser plasma in a solid target.

Coherent far-IR radiation is observed upon the generation of dense laser-driven plasma in a solid copper target. The coherent radiation demonstrates a strong half-cycle-pulse nature with temporal dynamics as fast as 150 fs. Comparisons between the data and radiation models are discussed. This measurement demonstrates a new method of performing ultrafast laser-plasma diagnostics in solid targets.

Single-shot two-dimensional spectrometer.

A two-dimensional optical spectrometer is demonstrated using simple optical components. This spectrometer is based on ultrafast two-dimensional (2D) frequency-dispersed pump-probe spectroscopy and can be used for single-shot correlation spectroscopy. To demonstrate functionality of this device, we measure the 2D correlation spectrum of atomic rubidium.

Upconversion multichannel infrared spectrometer.

A multichannel IR spectrometer using a standard silicon CCD array is demonstrated. Sum frequency generation between an ultrafast optical pulse and a frequency-dispersed IR beam generates a spatially extended optical signal that is collected on a generic CCD video camera. This method provides an inexpensive and efficient alternative to conventional multichannel IR arrays.

X-ray synchrotron studies of ultrafast crystalline dynamics.

Ultrafast X-ray experiments at synchrotron sources hold tremendous promise for measuring the atomistic dynamics of materials under a wide variety of transient conditions. In particular, the marriage of synchrotron radiation and ultrafast laser technology is opening up a new frontier of materials research. Structural changes initiated by femtosecond laser pulses can be tracked in real time using time-resolved X-ray diffraction on picosecond time scales or shorter. Here, research at the Advanced Photon Source is described, illustrating the opportunities for ultrafast diffraction with some recent work on the generation of impulsive strain, coherent phonon generation and supersonic diffusion of electron-hole plasmas. The flexibility of time-resolved Bragg and Laue diffraction geometries are both utilized to illuminate the strain generation and evolution process. Time-resolved X-ray science will become increasingly important with the construction of linac-based ultrafast X-ray sources.