Physical Society Colloquium

Ultrafast THz Light-Matter Interactions

David Cooke

Department of Physics
McGill University

Our lab performs ultrafast spectroscopy on materials in the 0.3 - 30 THz part of the electromagnetic spectrum. These photons are about 1000 times lower in energy than the photons you are using to read this right now. This window encompasses a huge range of fundamental excitations in condensed matter, as well as their scattering rates, making it a type of “sweet spot” for interesting materials-based physics. The energetics, and non-equilibrium dynamics, of these excitations are often important to optoelectronic devices such as solar cells, e.g. how charges are generated when light is absorbed and how easily this charge migrates through a material. Using advanced nonlinear optical methods and ultra-short pulsed lasers, we can spectroscopically probe these excitations as they are created, evolve and die with sub-50 femtosecond temporal resolution.

In this talk I go through the techniques we use to generate and detect single cycle pulses of THz frequency light and describe how we use them to spectroscopically probe dynamics in materials. I discuss our work over the years on generating extremely intense THz pulses with peak field strengths approaching MV/cm, strong enough to drive materials into the “extreme” nonlinear optical limit. We also review a new technique developed in our lab to arbitrarily shape these THz fields in time, useful for controlling nonlinear interactions but also potentially for high speed wireless communications. Finally, I discuss the direction my lab is taking in the next few years, from THz-driven particle acceleration to optical control of emergent states.