Fiber crystal growth from the melt for non-linear optical applications
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Fiber crystal growth from the melt for non-linear optical applications Michel Ferriol • Marianne Cochez
Phase-Equilibria Special Chapter Akade´miai Kiado´, Budapest, Hungary 2012
Abstract During several years, we have been involved in the growth and characterization of non-linear optical crystals by the two most common techniques for growing single-crystal fibers from the melt: laser-heated pedestal growth and micro-pulling down. Their specific features are presented in this study and their versatility is demonstrated through two typical examples of incongruently melting materials: K3Li2-xNb5?xO15?2x (solid solution of the ternary system K2O–Li2O–Nb2O5) and Ca5(BO3)3F which can only be grown from a flux. Keywords Laser-heated pedestal growth Micro-pulling down Single-crystal fiber Nonlinear optical materials Niobates Borates
Introduction The solid-state laser industry has an increasing need for small light sources with high efficiency. Fiber-shaped crystals (0.1–10 mm) would help in meeting these requirements. Single-crystal fibers have a shape favorable to light propagation and present a laser beam with better quality and reliability than diodes. Moreover, one of the advantages of single-crystal fiber lasers, as compared to commercially available double-clad amorphous fiber-based lasers, is associated with the possibility of increasing the core dimension. This allows to obtain strong pulses under Q-switching operation or large continuous wave powers.
M. Ferriol (&) M. Cochez Laboratoire Mate´riaux, Optiques Photonique et Syste`mes, Universite´ de Lorraine, E.A. 4423, 57070 Metz, France e-mail: [email protected]
Furthermore, obtaining some wavelengths not directly attainable by laser effect requires the use of frequency converters (for doubling and/or frequency summing). For example, it is the case for UV lasers as no direct UV laser effect can be produced in any crystal. The goal of this study is to present some selected results from our previous works about the growth, structural and chemical characterization of non-linear optical singlecrystal fibers for the generation of green, blue, or UV light by conversion of an IR source.
Single-crystal fiber growth The two most common methods of growing single-crystalline fibers from the melt are laser-heated pedestal growth (LHPG) [1, 2] and micro-pulling-down (l-PD) [3]. Each of them has some specific features which will be emphasized in the following. Laser-heated pedestal growth (LHPG) It was developed at Stanford University (USA) by Prof. R.S. Feigelson and M.M. Fejer in the eighties. In this technique, a CO2 laser beam (10.6 lm) is focused on the tip of a ceramic source rod of the material to be grown. The laser beam has a ring shape obtained by means of circularly symmetric laser optics [4, 5] producing a homogeneous circular distribution of radiation on the rod. When melting is obtained, a seed (single crystal or sintered rod) of smaller diameter than the source rod is dipped into the molten zone maintained in equilibrium owing to in
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