Light Aided Domain Patterning and Rare Earth Emission Based Imaging of Ferroelectric Domains
Trivalent rare earth and transition metal ions in insulating materials have been the topic of extensive investigations over the years due to their application as active ions in solid-state lasers. In lithium niobate (LiNbO3) with its favorable nonlinear a
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Light Aided Domain Patterning and Rare Earth Emission Based Imaging of Ferroelectric Domains V. Dierolf and C. Sandmann
6.1 Introduction and Background 6.1.1 Overview Trivalent rare earth and transition metal ions in insulating materials have been the topic of extensive investigations over the years due to their application as active ions in solid-state lasers. In lithium niobate (LiNbO3 ) with its favorable nonlinear and electro-optical properties, Er ions and other rare earth ions have been utilized in integrated optical lasers and optical amplifiers (see, e.g., [1–4]). In this chapter, we want to summarize a shift of focus from studying the properties of the defect ions for their own sake to applying the acquired knowledge and using the ions as probes to study the properties of the host material. In particular, we will highlight the use of erbium (Er3+ ) and other rare earth ions as probes for local electrical fields and defect configurations that are found in integrated optical devices such as periodically poled wave-guide devices. In the latter, the introduction of, e.g., Ti ions for waveguide production and the domain inversion process induces changes in the local structure of the material that can be probed using emission spectra of the Er ions and exploited for imaging purposes. With this nondestructive imaging technique, we can demonstrate that the observed changes are not independent of each other and that this interaction needs to be considered for precise device fabrication.
V. Dierolf Physics Department, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015, USA e-mail: [email protected] C. Sandmann (B) BD, 1 Becton Drive, Franklin Lakes, NJ 07417, USA e-mail: [email protected] C. Sandmann e-mail: [email protected] P. Ferraro et al. (eds.), Ferroelectric Crystals for Photonic Applications, Springer Series in Materials Science 91, DOI 10.1007/978-3-642-41086-4_6, © Springer-Verlag Berlin Heidelberg 2014
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V. Dierolf and C. Sandmann
We will use Er ions as the prime example throughout this chapter because this ion is the one most commonly used in devices such that suitable samples were more easily available to the authors. The unprecedented degree of control of the local electric fields obtained with this probe further allowed the development of a laser-aided domain inversion writing process, which offers the promise of sub-micron structure with precise dimensions as needed in next-generation nonlinear and electro-optical devices.
6.1.2 Rare Earth Ions in LiNbO3 Erbium belongs to the group of rare earth ions for which the 4f shell is continuously filled. For more details, see, e.g., [5]. The 4f electrons are well shielded from external fields by the completely filled 5s2 and 5p6 shells which have a larger radial extension than the 4f shell. The neutral rare earth atoms have, in addition to the filled shells and the 4f shell, two or three electrons in the 5d and 6s shells. These electrons are removed first during ionization. In the case of a trivalent ion, which is the most common valen
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