Confocal two photon emission microscopy: A new approach to waveguide imaging

Based on earlier studies of the interaction effects between Er3+ and Ti4+ ions in Ti:LiNbO3 waveguides we investigated the feasibility of using the Er3+ as a sensitive probe to determine Ti4+-diffusion profiles with high spatial resolution. Using a home-built confocal microscope combined with site-selective optical spectroscopy we tested two different operation modes: (i) Evaluating the emission spectra obtained by one-step excitation with a single laser we obtain high resolution (≈700 nm) Ti4+-concentration images. In particular using the second moments of the spectra, which turn out to be approximately linearly related to the Ti4+-concentration, we obtain very good contrast with essentially no artifacts caused by topology, intensity fluctuations, and Er3+ ion concentration profile. (ii) Measuring the total emission intensity under a specially chosen two step excitation scheme allows to selectively excite regions with a certain Ti4+ concentration. While for (i) a calibration can be done, for (ii) this will be hard due to the multi-site character of the Er3+ in LiNbO3.