Structured all-optical domain inversion in iron-doped lithium niobate

Recently, a promising technique for all-optical domain inversion in photovoltaic lithium niobate by visible laser irradiation has been demonstrated. However, only Gaussian light beams have been used to induce the inversion process. Here, we successfully exploit this emergent technique with structured light to fabricate a variety of 2D domain patterns. We use amplitude-modulated continuous-wave visible laser light controlled by a spatial light modulator. Our analysis investigates the relationship between domain growth dynamics and exposure parameters. Domains are evaluated using 3D second-harmonic generation laser scanning microscopy, second-harmonic generation k-spectroscopy, and scanning electron microscopy. The results demonstrate that initial nanodomain growth aligns with crystallographic directions, while the final domain shapes are influenced by both the amplitude of the induction light field and the exposure duration. By controlling light exposure, we create uniform single and multiple spatially shaped domains with lateral extensions ranging from 300 nm to over 400 μm. The correlation between domain formation dynamics and second-harmonic nonlinear diffraction measurements indicates the effectiveness of this structuring method for shaping quasi-phase-matched optical processes.