Crystals of vanillin-3,5-dinitrosalicylic acid: synthesis, bulk growth, extensive characterisation and enhancement of self-defocussing properties by shock wave for high-performance nonlinear optical and photonic devices

Single crystals of vanillin-3,5-dinitrosalicylic acid (VDNS) were grown using slow cooling in ethanol solvent and subjected to shock waves (Mach 1.2) generated by a supersonic low-energy table-top shock tube. All characterisations were given in a comparative fashion, highlighting differences with and without shock wave application. Under shock wave loading, dielectric dispersion increased, indicating enhanced dipolar polarisation. Etching studies confirmed fine crystal perfection despite shock exposure. Classical nucleation theory was applied to evaluate nucleation parameters such as phase strain, Gibbs free energy, and critical radius under shock-induced conditions. Vickers microhardness testing revealed improved mechanical stability, supported by the Hays-Kendall model, indicating shock-induced densification. The laser damage threshold (LDT) increased, showing enhanced optical durability. Optical band gap (∼3 eV), refractive index dispersion (Sellmeier and Wemple–DiDomenico models), and Urbach energy were also affected by shock waves, pointing to a reduction in defect states. Shock exposure further improved nonlinear optical properties as observed through Z-scan analysis and introduced novel photoelastic behavior.