Noncentrosymmetry Observed in CaC₄H₄O₆ · 4H₂O Crystals by Nonlinear Optical Measurements

Calcium tartrate tetrahydrate (L‐CTT) is reported to have point group symmetry mmm at room temperature. Second harmonic generation experiments indicate that calcium tartrate tetrahydrate prepared from pure L‐tartaric acid has the noncentrosymmetric point group mm2. All the nonlinear optical d ‐coefficients are determined. Linear optical properties of this material such as: refractive indices and absorption constant are measured in the range 200 nm < λ < 2000 nm and the phase matching conditions for optical frequency doubling are derived. Non critical type I phase matching can be achieved in L‐CTT at room temperature for a fundamental wavelength of λ = 816 nm.