Optical Second-Harmonic Generation in Paratellurite and Kleinman's Symmetry Relations

The second harmonic of a 1.064-μ Nd3+ YAG laser has been observed in paratellurite This effect is forbidden by Kleinman's relations. The only nonvanishing nonlinear coefficient d14 has been measured relative to quartz by the Maker-fringe technique and to KDP under phase-matching conditions. It has been inferred that d14=1.4×10−9 esu and δ14=3.8×10−8 esu. The latter value is 40 times lower than the average over all the known materials.