Extracting Anharmonic Coupling Constants from Beta-Barium Borate

Multidimensional terahertz (THz) spectroscopy is a powerful tool for understanding nonlinear excitation, coherent energy flow, and coupling between collective degrees of freedom on ultrafast time scales. With extreme vibrational excitation using high-field THz light, 2D THz spectroscopy can reveal how anharmonic mode coupling results in coherent energy transfer. We explore phononic coupling between modes in β-barium borate and attempt to extract the coupling constants.