Correlation of large SHG responses with structural characterization in borophosphate niobium glasses

Transparent and homogeneous sodium borophosphate niobium glasses with good optical quality were obtained for Nb2O5 proportion up to 50 mol%. Large NLO second-order susceptibilities, up to ∼5 pm/V for the highest niobium loading, are generated through an efficient thermal poling process which induces a strong space-charge migration of Na+ cations. From combined IR, Raman and thermal analyses, we establish that the observed strong increase of χ(2) responses with niobium concentration is linked to the extent of the niobium-oxygen 3D structure which enhances the third-order susceptibility.