Ultrafast Polarization Modulation Driven by above-Bandgap Photoexcitation in Ferroelectric NbOCl ₂

Understanding the dynamics of ferroelectric polarization switching under external stimuli is crucial for optimizing device performance, particularly in terms of operating speed and bandwidth. Here, we employ time-resolved second-harmonic generation (SHG) spectroscopy to probe ultrafast optically driven polarization modulation in bulk NbOCl₂. Upon above-bandgap photoexcitation, a significant suppression of the SHG intensity occurs within subpicosecond time scales. The maximum modulation depth of the ferroelectric polarization reaches nearly 50% and scales linearly with pump fluences up to 10 mJ/cm², reflecting the high stability of both electronic and lattice subsystems in NbOCl₂. Supported by time-resolved reflectivity measurements, our findings reveal that polarization dynamics are primarily governed by photocarrier screening coupled with transient electron heating. These results highlight the promise of NbOCl₂ for applications in high-speed optically controlled ferroelectric devices.