Inhomogeneous and homogeneous broadening in Pr/sup 3+/- and Er/sup 3+/-doped lithium niobate

Abstract

Summary form only given. Congruent lithium niobate has a disordered, lithium-deficient structure in which Nb/sub Li/ antisites provide charge compensation for lithium vacancies. The disorder is produced by departures from stoichiometry, which play an important role in the photorefractive properties of lithium niobate, particularly two-color photorefractivity at ambient temperatures. Disorder also increases the inhomogeneous linewidth (/spl Gamma//sub inhom/) of optical transitions of impurity centers, which gives a desirable increase in bandwidth for applications involving low temperature spatial-spectral holography where the frequency and time-domain phenomena of spectral hole burning and photon echoes are combined with that of spatial holography. However it also has the potential to increase the homogeneous linewidth (/spl Gamma//sub hom/) by inducing low frequency tunneling modes or "two-level systems" (TLS), reducing the figure of merit for the time-bandwidth product: F=/spl Gamma//sub inhom///spl Gamma//sub hom/. We investigate the role of disorder in lithium niobate by measuring both the inhomogeneous and homogeneous broadening of optical transitions in Pr/sup 3+/ and Er/sup 3+/ doped lithium niobate where the rare-earth ions are generally accepted to substitute for Li/sup +/ ions in sites of nominally C/sub 3/ symmetry.