Examining Nonlinear Terahertz Photonic and Phononic Excitation with Two-Dimensional Spectroscopy

We use high-field, broadband terahertz (THz) pulses to nonlinearly excite a set of Raman active modes in centrosymmetric crystals. Using two-dimensional (2D) THz spectroscopy we can investigate photonic and phononic excitation and isolate the dominant and secondary nonlinear excitation pathways. We present a general framework for 2D THz vibrational spectroscopy in solid systems that provides important clarification for the growing new field of nonlinear phononics.