Lithium d‑Isoascorbate Monohydrate, a New Nonlinear Optical Material

Single crystals of lithium d-isoascorbate monohydrate (LDAM), (C6H7O6Li·H2O), are grown by a solution growth method. The crystal structure of LDAM is solved using single crystal X-ray diffraction. The space group is orthorhombic P212121 with four formula units per unit cell and lattice parameters a = 7.7836(3) Å, b = 8.7456(3) Å, and c = 11.0368(4) Å. Solubility of the material in water is determined thermogravimetrically and found to have a positive temperature coefficient of solubility. Large optical quality single crystals are subsequently grown from aqueous solution by a slow cooling method. The crystal has a bulky prismatic habit and among the prominent faces the c face appears as the only principal morphological face. The crystal exhibits a (010) cleavage. Dielectric spectroscopy reveals a nearly Debye type Cole–Cole behavior with anisotropy in relaxation. Optical transmission range is found to be from 300 to 1400 nm. The principal refractive indices of this biaxial crystal, measured using Brewster’s angle method, at wavelengths 405, 543, and 632.8 nm, show high dispersion. The crystal is negative biaxial with 2Vz = 107.8° (405 nm) and belongs to the Hobden class 3. Theoretically generated type 1 and type 2 second order phase matching curves match very well with the experimental results. The second-order nonlinear coefficient d14 was determined to be 7 × 10–13 m/V. For the optimum phase matching direction (type 2), the second-order effective nonlinear coefficient and the walk off angle are determined to be 0.84 times d14 and 3.5° respectively. The crystal possesses high multiple surface damage thresholds of 18 GW/cm2 and 8 GW/cm2 at laser wavelengths 1064 and 532 nm, respectively.