Nonlinear optical potential of engineered sodium d-isoascorbate monohydrate single crystals: a comprehensive characterization study†

Sodium D-isoascorbate monohydrate (NDIAM) single crystals were successfully grown from a customised slow cooling technique, and were found to have excellent structural quality, as confirmed by single crystal X-ray diffraction (SXRD) and powder XRD analyses. The crystals are extremely transparent in the visible to near-infrared region, and have a wide optical bandgap of 4.12 eV which makes them ideal for optical applications that require low signal loss. The dielectric studies, along with theoretical polarizability models, indicate a strong dipolar response, which enhances the nonlinear optical (NLO) interactions. Notably, the crystal shows negative photoconductivity, exhibits thermal stability up to 152 °C, and a high laser damage threshold of 5.2 × 10⁸ W cm⁻², which supports its use in high-power laser environments. NLO studies demonstrated that NDIAM possesses good second harmonic generation (SHG) efficiency, which is 1.85 times greater than the standard KDP crystal. Furthermore, third harmonic generation (THG) analysis shows that NDIAM has a positive refractive index and displays multi-phonon absorption behaviour.