Some Optical Properties of LiNbO3:Gd3+(0.003):Mg2+(0.65 wt %) Single Crystal: A Promising Material for Laser Radiation Conversion

Abstract

A nonlinear optical double-doped single-crystal LiNbO3:Gd:Mg (Gd concentration is 0.003, Mg—0.65 wt % in the crystal) has been researched by several optical methods: laser conoscopy, photoinduced light scattering (PILS), optical spectroscopy, and Raman scattering. The crystal has been shown to have no photorefraction effect and a high optical uniformity. Fine features of the crystal structure have been studied via Raman spectra. Spectra have been registered in the first and second orders, they have been excited by visible (532 nm) and near-IR (785 nm) lasers. Registered Raman spectra have the fundamental vibrations of the crystal lattice of the A1(TO,LO)- and E(TO,LO)-type symmetry located in the range of 150–900 cm−1. A number of low-intensity Raman bands in the 900–2000 cm−1 region have been determined to correspond to the second-order Raman spectrum. These bands are polarized and appear only in certain polarization-scattering geometries. They appear in the spectrum excited by visible radiation, but their number and intensity are much lower than those excited by near-IR lasers. Oxygen-octahedral MeO6 clusters in our case can contain Li, Nb, Gd, or Mg in the Me site. The clusters in the LiNbO3:Gd:Mg crystal structure are slightly distorted compared with similar clusters in the nominally pure LiNbO3 crystal. It has been established that the value R = [Li]/[Nb] in the studied crystal is ≈ 1. Such a ratio usually characterizes a nominally pure stoichiometric crystal.