Emission and Absorption Cross-Sections of Mg/Er-Codoped Near-Stoichiometric ${\rm LiNbO}_{3}$ Crystals

Near-stoichiometric (NS) (Mg:)
${\rm Er}{\colon}{\rm LiNbO}_{3}$
crystals were grown from melts
$([{\rm Li}_{2}{\rm O}]{\colon}[{\rm Nb}_{2}{\rm O}_{5}]=1{\colon}1)$
containing 0.0/0.5, 0.5/0.5, and 1.0/0.5 mol%/mol%
${\rm MgO}/{\rm Er}_{2}{\rm O}_{3}$
. OH absorption study shows that the optical damage threshold Mg concentration of the Er/Mg-codoped NS crystal is just near 1.0 mol%. Polarized visible and near infrared, and unpolarized mid-infrared
$\left(2.7\,\mu {\rm m},^{4}{\rm I}_{11/2}\rightarrow ^{4}{\rm I}_{13/2}\right)$
emission spectra of
${\rm Er}^{3+}$
ion in these crystals were measured. From measured emission spectra, the emission and absorption cross-section spectra were calculated based upon McCumber theory, and compared with the data of congruent
${\rm Er}{\colon}{\rm LiNbO}_{3}$
bulk material and/or Ti-diffused
${\rm Er}{\colon}{\rm LiNbO}_{3}$
strip waveguide and the results obtained from the direct unpolarized optical absorption measurements. The 550, 980, and 1530 nm emission lifetimes were also measured, and compared with the Judd-Ofelt theoretical values and the measured values of the congruent material. The results show that the polarized absorption cross-section data derived from the emission spectra are comparable to the unpolarized cross-section data from direct absorption measurements. The emission and absorption cross-sections, their polarization dependences as well as the lifetime all change definitely as the crystal composition shifts from the congruent point to the near-stoichiometry. In the NS crystal, the
${\rm Er}^{3+}$
ion has smaller emission and absorption cross-sections, and longer lifetimes. In contrast, MgO codoping has less effect on the emission and absorption cross-sections, and lifetime.