Optically Driven Formation of Tailored Phonon Cavities.

Optical control of lattice dynamics with high spatiotemporal precision offers a route to manipulate local quantum states-such as magnetic, spin, and topological states-by exploiting the coupling between the lattice and other degrees of freedom. Here, deterministic strain engineering is demonstrated with spatial and temporal characteristics in van der Waals materials using spatially structured femtosecond optical fields. By confining structural oscillations at a submicron scale, phonon cavities with programmable dimensions, oscillation periods, and symmetries are engineered. Through ultrafast electron microscopy analysis and finite-element simulations the dominant cavity modes, out-of-plane confined oscillations, and in-plane Lamb waves are directly imaged and identified. It is shown that the properties of these phonon cavities are programmable via the spatial profile of the optical excitation, enabling localized modulation of strain and lattice displacement at nanometer and picosecond scales. This work establishes a general framework for spatiotemporal phonon engineering, bridging structured light excitation with atomic-scale control of lattice dynamics.