Absorption and fluorescence anisotropies of monoclinic crystals : the case of Nd:YCOB Yannick Petit 1, Benoît Boulanger 1*, Patricia Segonds 1, Corinne Félix 1 Bertrand Ménaert 1, Julien Zaccaro 1, Gérard Aka 2 1
Institut Néel CNRS/UJF, 25 rue des Martyrs, BP 166, F38402 Grenoble Cedex 9 France 2 Ecole Nationale Supérieure de Chimie de Paris, Paris France *Corresponding author:
[email protected]
Abstract: We report for the first time measurements and modelization of the angular distributions of absorption and fluorescence in a monoclinic crystal. Studies on Nd:YCOB revealed specific topologies with ombilics. These new data upgrade the knowledge on low symmetry crystal optics. ©2008 Optical Society of America OCIS codes: (260.2510) Fluorescence; (160.3380) Laser materials; (160.4760) Optical properties.
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1. Introduction The potentiality of new laser crystals relies on a complete characterization of their absorption and fluorescence properties. These two effects are governed by the imaginary part of the complex permittivity εˆ that is described by a polar second rank tensor, the real part of εˆ being related to the refractive index. When laser crystals belong to cubic crystal classes, like Nd:YAG for example [1], the three main values of εˆ are equal, leading to optical properties that are independent to the crystal orientation. But, nowadays, there are promising laser materials that are anisotropic, like for example the uniaxial crystals Nd:YLiF4 and Nd:YVO4 [1], or the biaxial ones Yb:GdCOB [2] and Nd:YCOB [3]. For these crystals the tensors of the real and imaginary parts of εˆ can have up to three different main values each, so that the absorption and fluorescence angular distributions are expected to be anisotropic, as it is the case for the refractive index [4]. Here we theoretically and experimentally considered the case of a monoclinic crystal class, and Nd:YCOB is investigated. We report, for the first time to #92832 - $15.00 USD
(C) 2008 OSA
Received 15 Feb 2008; revised 13 Apr 2008; accepted 14 Apr 2008; published 19 May 2008
26 May 2008 / Vol. 16, No. 11 / OPTICS EXPRESS 7997
the best of our knowledge, that the angular distributions of the two polarization components of the absorption coefficient and of the fluorescence power exhibit singularities of the same kind than those of the biaxial index surface. Furthermore, we show that the main values of absorption and fluorescence are not along the principal axes of the dielectric frame, but respectively along the principal axes of two new frames tilted from the dielectric frame. 2. State of the Art : absorption of anisotropic high symmetry crystals A complete description of absorbing anisotropic crystals had been reported by introducing a complex permittivity εˆ = ε + jε ' in the equations of the propagation of light, where ε is related to the refractive index and ε’ governs absorption [4]. The discussion had been confined to anisotropic crystals belonging to high symmetry crystal classes, i.e. hexagonal, tetragonal, trigonal or orthorhombic classes. In these cases, the real and imaginary parts of εˆ are described by polar second rank tensors that are both diagonal in the dielectric frame [4]. The analysis was considerably simplified by assuming ε’
