Polar potassium rare earth nitrates K-2[RE(NO3)(5)(H2O)(2)] (RE = La, Ce, Pr and Nd). II. Linear and nonlinear optical properties

Linear and nonlinear optical properties of the four isomorphic orthorhombic (point group mm2) potassium rare earth nitrates K-2[RE(NO3)(5)(H2O)(2)], w ith RE = La, Ce, Pr or Nd, have been investigated. Refractive indices in a wavelength range from 0.35 to 2.5 mu m and the transmission spectra between 0.25 to 3.0 mu m were measured. Using the Maker fringe technique, the d(ij k)(SHG) coefficients of second-harmonic generation for a fundamental of the Nd-YAP laser (lambda = 1079.5 nm) were determined for all four compounds. The d(ijk)(SHG) coefficients of all four substances are about three times l arger than those of KDP, as was first published by Ebbers et al. [IEEE J. Q uantum Electron. (1993), 29, 497-507] for K-2[La(NO3)(5)(H2O)(2)]. These ni trates are promising materials for application to nonlinear optics (e.g. se cond-harmonic generation of Nd laser radiation). The nonlinear optical prop erties of these compounds seem to have their origin mainly in the nitrate g roups, as indicated by a simple model (summing the molecular hyperpolarizab ilities of the NO3 group). Neglecting local field effects, the hyperpolariz ability of the NO3 group was calculated as beta(222) = 2.52 x 10(-40) m(4) V-1. (C) 2000 International Union of Crystallography Printed in Great Brita in - all rights reserved.