Microscopic nonlinear optical response: Analysis and calculations with the Floquet-Bloch formalism

We analyze microscopic nonlinear optical response of periodic structures within the Floquet-Bloch formalism. The analysis is focused on the real-space distributions of optically induced charge and electron current density within the unit cell of a crystal. We demonstrate that the time-reversal symmetry of a crystal determines the phases of the temporal oscillations of these distributions. We further analyze their spatial symmetries and connection to macroscopic optical response. We illustrate our study with ab initio calculations that combine density functional theory with the Floquet-Bloch formalism. The calculations provide time-dependent optically induced charge distributions and electron current densities within the unit cells of a crystal with inversion symmetry $$ and a crystal without inversion symmetry $$ in response to a strong-field excitation. The real-space, microscopic view on nonlinear optical response provides insightful information about the strong field-matter interaction.