Optical and Ferroelectric Properties of Barium Sodium Niobate

Abstract

Optical absorption, refractive index, dielectric constant, nonlinear optical coefficients, and linear electro-optic coefficients are reported for single-domain crystals of ${\mathrm{Ba}}_{2}$Na${\mathrm{Nb}}_{5}$${\mathrm{O}}_{15}$ between room temperature and the Curie temperature. Orthorhombic ($\mathrm{mm}2$) barium sodium niobate, a filled tungsten-bronze structure, is stable to intense laser radiation, and its phasematchable nonlinear coefficients are 3 times those of LiNb${\mathrm{O}}_{3}$ and LiI${\mathrm{O}}_{3}$. For the 1.064-\ensuremath{\mu}m laser fundamental, the observed phase-match temperatures and the angular half-widths of the phase-matched second-harmonic intensity due to the coefficients ${d}_{31}$ and ${d}_{32}$ are found to be in good agreement with the values calculated from refractive-index data. The dielectric constant and electro-optic half-wave voltage data indicate that ${\mathrm{Ba}}_{2}$Na${\mathrm{Nb}}_{5}$${\mathrm{O}}_{15}$ is a useful electro-optic modulator material. The temperature variation of the spontaneous polarization ${P}_{S}$ is deduced from the birefringence, electro-optic, nonlinear optical, and pyroelectric data. It is concluded that the ferroelectric transition in ${\mathrm{Ba}}_{2}$Na${\mathrm{Nb}}_{5}$${\mathrm{O}}_{15}$ is of the first order.