Site-selective measurement of relaxation properties at 980 nm in Er $$^{3+}$$ 3 + -doped congruent and stoichiometric lithium niobate crystals

Abstract

A pump-probe-type saturation spectroscopic experiment has been performed at 980 nm to measure the homogeneous linewidth of the $$^4$$ I $$_{11/2}$$ – $$^4$$ I $$_{15/2}$$ transition and the lifetime of the $$^4$$ I $$_{11/2}$$ state of erbium embedded into lithium niobate single crystals. There are several non-equivalent Er $$^{3+}_{\mathrm{Li}^+}$$ –V $$_{\mathrm{Li}^+}$$ sites with differently oriented defect structure for charge compensation. These non-equivalent centers differ in their transition energies. Hence, our measurements have been done at two nearby frequencies, addressing groups of erbium ions located at non-equivalent sites. The results are compared with lifetime calculations and measurements found in the literature and with the predictions of our simple model calculation.