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.