Investigation of the second-harmonic generation (SHG) phase-matching loci for the low- symmetry monoclinic (P21) N-(4-nitrophenyl)-(L)- prolinol (NPP) crystal1 has indicated the contribution of the molecular electronic structure to the rotation of the principal dielectric axes. These investigations have been undertaken with gel-grown NPP crystals obtained by slow cooling of a saturated gelled solution.2 Owing to gelled medium properties, gel growth allows for obtainment of nearly defect-free crystals of reproducible quality. Most NPP gel-grown crystals exhibit a single twin along the (101) contact plane connecting two crystalline individuals. X-ray topographs (Fig. 1) show the good crystalline quality with misorientation between the two individuals smaller than 1’.
© 1991 Optical Society of AmericaPDF Article