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

Area of Science:

• Condensed matter physics
• Quantum optics
• Materials science

Background:

• Nonlinear optical response is crucial for understanding light-matter interactions in materials.
• Periodic structures exhibit complex behaviors under strong optical fields.
• Microscopic details of charge and current dynamics are key to macroscopic optical properties.

Purpose of the Study:

• To analyze the microscopic nonlinear optical response of periodic structures.
• To investigate the role of time-reversal and spatial symmetries in optical phenomena.
• To connect real-space charge and current distributions to macroscopic optical response.

Main Methods:

• Utilizing the Floquet-Bloch formalism for analyzing periodic structures.
• Focusing on real-space distributions of optically induced charge and electron current density.
• Employing *ab initio* calculations combining density functional theory (DFT) with the Floquet-Bloch formalism.

Main Results:

• Demonstrated that time-reversal symmetry governs the phase of temporal oscillations in charge and current distributions.
• Analyzed spatial symmetries of these distributions and their link to macroscopic optical response.
• Calculated time-dependent charge and current densities for crystals with and without inversion symmetry under strong-field excitation.

Conclusions:

• The real-space, microscopic perspective offers significant insights into strong field-matter interactions.
• Understanding microscopic dynamics is essential for predicting and controlling macroscopic nonlinear optical responses.
• Symmetry properties play a fundamental role in determining the nature of nonlinear optical phenomena.