Prof. Dr. Adrian L. Cavalieri
We investigate ultrafast dynamics occurring in atomic, molecular and solid-state systems. Of particular interest are optically driven electronic dynamics in materials, which may occur on the attosecond timescale and can directly precede comparatively slower, femtosecond structural dynamics and bulk phase transitions. Ultimately, our goal is to exert coherent control over these phase-transitions, allowing for future device development with material properties that can be switched within femtoseconds.
For our experiments, we utilize both table-top and large-scale free-electron laser sources (FELs) for attosecond-to-femtosecond time-resolved photoelectron spectroscopy, absorption spectroscopy, X-ray resonant scattering and X-ray diffraction.
In the laboratory, the driver for our table-top experiments is an octave spanning laser, producing near single-cycle pulses that can be converted by a variety of nonlinear optical processes including, optical rectification, sum-frequency generation, difference frequency generation, and high-harmonic generation to cover an extremely broad region of the electromagnetic spectrum. With laser light spanning the THz and far-infrared to the extreme ultraviolet (XUV), targeted femtosecond to attosecond dynamics can be both driven and interrogated.
At large-scale free-electron laser facilities, like the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory in California, the possibilities for both pumping and probing systems are expanded to the hard X-ray regime. Yet, for all of their flexibility – in photon energy and pulse duration and intensity – these sources present significant technical challenges in timing and stabilization that must be dealt with to access their full potential. We have been at the forefront of advanced instrumentation development for applications at FEL facilities since they were first commissioned in the soft x-ray regime in 2005 at DESY and in the hard-X-ray regime in 2009 at SLAC. Today, using our own diagnostics, we are among the first users to fully take advantage of sub-5 fs X-ray pulses at LCLS to directly observe inner atomic and molecular electron dynamics.