Seminar: First-Principles Calculation of Time-Resolved Spectroscopic Observables in Ultrafast Experiments

Understanding how light interacts with quantum materials on femtosecond timescales requires bridging ultrafast spectroscopy and first-principles theory. In this talk, I present a unified computational framework for calculating spectroscopic observables in time-resolved experiments, including transient magneto-optical Kerr effect (MOKE), time-dependent X-ray absorption (XAS), X-ray magnetic circular dichroism (XMCD), and terahertz (THz) conductivity. The approach combines time-dependent density-functional theory with real-time response formalism, enabling the extraction of transient optical and magnetic response functions directly from the evolving electronic structure. Applied to both ferromagnetic and topological materials, the framework reveals how laser excitation reshapes magnetic order, spin textures, and topological band connectivity through band renormalization and Berry curvature dynamics. By comparing calculated transient spectra to experimental data, we identify distinct microscopic pathways—spin transfer, spin-orbit–driven demagnetization, and topological phase reshaping—that govern the ultrafast evolution of magnetic and topological states.