Ultrafast Terahertz Light-Matter Interactions

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This research program merges ultrafast laser science and condensed matter physics, using pulses of terahertz (THz) frequency light to measure and control electronic degrees of freedom in materials on sub-picosecond time scales. The light-matter interaction in this low energy 0.1 - 30 THz regime is dominated by the motion of free and bound charges, collective excitations and low energy gaps arising in exotic states such as superconductivity. We use advanced nonlinear optical techniques and femtosecond laser sources to generate phase stable, few cycle THz pulses of light that allow energy and time-resolved snapshots of these excitations. We use our methods to help provide an improved understanding of novel solar cell materials, where THz allows one to quantitatively measure photoconductivity, exciton and lattice dynamics simultaneously, on unmatched sub-ps time scales after light is first absorbed. We will target the new organometallic halide perovskite materials that have taken the solar community by storm, where the rapid development of devices outpaces the basic understanding of the materials themselves. Correlated electron materials exhibiting metal-insulator transitions resulting from competing or cooperating electronic and lattice contributions have puzzled condensed matter physicists for decades. Intrinsically sensitive to the metallic state, THz spectroscopy allows us to study these transitions on sub-ps time scales after they are triggered by an optical pulse or even another strong THz field. Separation of each contribution is then possible through their different dynamics, providing deep insight into the origin of their emergent properties. Increasing the peak electric and magnetic field strength of phase-locked THz pulses to MV/cm and near Tesla levels, respectively, enables a new method of time-domain control over charge and spin excitations on sub-cycle time scales, through interaction with engineered light fields. These extreme fields can be used to access hidden degrees of freedom in condensed matter that we will explore using a newly developed multi-dimensional nonlinear THz spectrometer. Finally, single-cycle, MV/cm pulses allow the generation of ultra-short bursts of energetic electrons from metal surfaces by overcoming the work function in the half-cycle of the THz pulse field. We will develop a new time-resolved electron energy loss spectrometer with electron pulse duration, energy and momentum controlled by THz optical fields. This program offers extensive training in ultrafast laser science, THz optics, materials physics and instrumentation development for 6 graduate students and numerous undergraduates with vibrant collaborations in Canada and abroad. Training emphasizes critical thinking, teamwork, communication and networking skills that support a successful research career in innovative areas of direct benefit to Canada.