Terahertz light-matter interactions: Revealing nonlinear dynamics of molecular rotations, spins, and lattice vibrations

Program Description
Nonlinear terahertz (THz) spectroscopy can reveal dynamics of material degrees of freedom beyond linear responses. In this talk, several examples of interactions between THz electric or magnetic fields and matter are presented. Rotations of polar molecules, spin dynamics in paramagnetic molecules and magnetically-ordered solids, and lattice vibrations in solids are studied. Two-dimensional THz spectroscopy of polar molecules and collective spin waves, including THz photon echoes, is demonstrated for the first time, which reveals multiple nonlinear interaction pathways. Couplings between THz- and Raman-active vibrational modes in a ferroelectric crystal are revealed by THz pump-optical probe spectroscopy. The methodology paves the way to ultrafast control of various material degrees of freedom by intense THz radiation.