Second and third order NLO studies in an organic crystal glucuronic acid γ-lactone.

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Detailed results of the linear and nonlinear optical properties in an organic NLO single crystal, Glucuronic acid c- Lactone (GAL) are reported. The dielectric axes of GAL were determined through conoscopy measurements. Once the x, y, and z directions were determined, the refractive indices of GAL along these directions were determined for several wavelengths. The dispersion in the refractive index was fitted to Sellmeir equations by which the refractive index at any wavelength could be calculated. Conic sections, formed due to spontaneous non-collinear second harmonic generation, were observed as two rings when projected onto a screen. This is a consequence of the GAL crystal being highly birefringent, and can be classified as a type II second harmonic crystal. By rotating the crystal and observing the rings on the screen, the direction of collinear phase matching was determined when these rings collapsed into an intense spot. This direction is the closest to the z-axis of the crystal by 14.85 in the anti-clockwise direction. The deff along this direction was calculated as 0.71 pm/V for input pulses of 1064 nm wavelength. This value is in comparison to that reported in many organic NLO materials and almost twice that of inorganic crystal KDP. From the closed aperture Zscan measurements, we observed that GAL possesses a negative nonlinear refraction and the value of n2 was obtained as 1013 cm2/W. The open aperture measurement reveals saturable absorption in GAL with a saturation intensity (Is) of 0.45 GW/cm2. The data converged only to two photon absorption and the 2PA coefficient (b) was obtained as 109cm/W. The magnitude of the nonlinear optical susceptibility v(3) was 1019 m2/V2. The large second and third-order nonlinear optical susceptibilities make GAL a potential candidate for various NLO applications.

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