Real-time and real-space tracking of coherent lattice vibrations using optical nonlinear spectroscopy

The probing of coherent lattice vibrations in solids has been conventionally carried out using time resolved transient or reflection spectroscopy where only the relative oscillation amplitude can be obtained. Here we demonstrate that, using standard optical nonlinear spectroscopy, electron-phonon and anharmonic phonon-phonon coupling and their relaxation dynamics can be probed in real time. In combination with optical deformable potential calculated from ab-initio density functional theory, our measurement with absolute amplitude information reveals the maximum, controllable displacement of neighbouring oxygen atoms in alpha-quartz crystal to tens of picometers in real space.