We use coherent light sources based on ultrafast pulsed laser technology to generate terahertz wave, mid- and near-infrared, and visible light to study the dynamics of light-induced nonequilibrium processes in a variety of materials. Particularly terahertz spectroscopy can reveal low-energy electromagnetic responses of materials on the range of millielectronvolts, which include crucial details for the dynamical motions of electron, phonon, or spin degrees of freedom in condensed matter physics. A novel route for optical control of materials by strong resonant or off-resonant excitation by light field has also been made possible by recently discovered powerful terahertz pulse production technology. We explore superconductivity or antiferromagnetism, gigantic nonlinearity of topological semimetals, and high-speed spin transport phenomena, in addition to the development of phase-stable terahertz generating and detection techniques and novel nonlinear spectroscopy schemes.

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