The Gao lab is a nonlinear spectroscopy group focused on quantum and energy materials. We develop cutting-edge ultrafast spectroscopy tools spanning the visible, mid-infrared, and terahertz spectral ranges, with the goal of probing and controlling novel physicochemical transformations in materials. These include inducing tunable hidden phases in quantum materials, directing energy-carrier dynamics in light-harvesting materials, and shaping chemical reactivity at catalytic and functional surfaces.