Extreme ultraviolet high-harmonic interferometry of excitation-induced bandgap dynamics in solids

Interferometry is a fundamental technique in physics, enabling precise measurements through the interference of waves. High-harmonic generation (HHG) in solids has emerged as a powerful method for probing ultrafast electronic dynamics within crystalline structures. In this study, we employed extreme ultraviolet (XUV) high-harmonic interferometry with phase-locked XUV pulse pairs to investigate excitation-induced bandgap dynamics in solids. Our experiments on amorphous SiO₂ and crystalline MgO, complemented by analytical modeling and semiconductor Bloch equation simulations, reveal a correlation between phase variations in harmonic emission that are consistent with bandgap modifications. These findings suggest a potential pathway for time-resolved, all-optical probing of band structure dynamics, advancing prospects for petahertz-scale electronic applications and attosecond diagnostics of carrier dynamics.