New phase-matchable nonlinear optical crystals of the formate family

New nonlinear optical orthorhombic formate crystals HCOONa and HCOOLi
0.9
Na
0.1
H
2
O have been grown from aqueous solutions in order to extend the transparency to the near infrared region. Their transmission characteristics, refractive indices, and Sellmeier's dispersion relations, together with nonlinear optical properties associated with second-harmonic generation (SHG), have been examined. By measuring second-harmonic intensities from these two crystals generated with a repetitively
Q
-switched Nd :YAG laser, we have derived the effective second-order nonlinearities d
eff
as a function of the phase-matching angles θ and φ. These compare favorably with the analytical result. The optimum SHG condition for both the Crystals can be determined through the analysis. HCOOLi
0.9
Na
0.1
. H
2
O mixed crystal is transparent from 0.24 to about 1.9 μm with wider infrared transmission compared with lithium formate. It is of practical interest for its useful second-order nonlinearity and easily-grown large crystals.