Nonlinear optics has recently emerged as an attractive approach for both probing topological properties and driving Dirac materials into new states. Here, I will describe our use of ultrafast nonlinear optics, especially at terahertz (THz) frequencies, to study three representative Dirac materials: graphene micro-ribbons, topological insulators, and Weyl semimetals. We used THz magneto-optical spectroscopy to examine periodic arrays of graphene micro-ribbons, enabling us to control the transmission and Faraday rotation spectra of THz pulses via coupling to discretized magnetoplasmon modes. In the Weyl semimetal TaAs, time-resolved second harmonic generation enabled us to reveal a new photoinduced phase, and THz emission spectroscopy was used to provide new insight into the circular photogalvanic effect. Finally, we used intense THz pulses to drive and coherently control structural dynamics in the topological insulator Bi2Se3. Overall, our studies demonstrate the utility of nonlinear optics in shedding new light on both static and dynamic properties of topological materials.

Biography: Dr. Rohit P. Prasankumar received a B.S. in Electrical Engineering from the University of Texas at Austin in 1997 and the M.S. and Ph.D. degrees in Electrical Engineering from MIT in 1999 and 2003, respectively. His thesis work, completed in 2003, concentrated on developing novel approaches for self-starting mode-locking in solid state lasers. Dr. Prasankumar subsequently performed his postdoctoral research at Los Alamos National Laboratory (LANL), focusing on ultrafast mid-to-far-infrared dynamics in semiconductor nanostructures and strongly correlated compounds. He has been a technical staff member at the Center for Integrated Nanotechnologies (CINT) at LANL since 2006, with research interests principally directed towards the measurement of dynamics in complex materials, such as multiferroics, semiconductor nanowires, and topological materials, with high temporal and spatial resolution over a broad spectral range. He is also a research associate professor at the University of New Mexico.