Techniques of observation and characterization of the domain structure in periodically poled lithium niobate
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. Gil Departamento Física de la Materia Condensada, C-III, Universidad Auto´noma de Madrid, E-28049 Madrid, Spain
L. Arizmendia) Departamento Física de Materiales, C-IV, Universidad Auto´noma de Madrid, E-28049 Madrid, Spain
J. Colchero and A.M. Baro´ Departamento Física de la Materia, Condensada, C-III, Universidad Auto´noma de Madrid, E-28049 Madrid, Spain
E. Die´guez Departamento Física de Materiales, C-IV, Universidad Auto´noma de Madrid, E-28049 Madrid, Spain (Received 10 April 2000; accepted 13 September 2000)
The domain structure of bulk periodically poled lithium niobate crystals were analyzed by different techniques. Images of topography, electrostatic force, and piezoelectric response were studied by scanning force microscopy. All these images showed the domain structure of the samples. The electrostatic force was always attractive pointing to a dielectric origin. The diffraction of a laser beam by the periodic structures was also observed, denoting a periodic change of refractive index. From the angle of diffraction the domain spatial frequency was directly obtained. The topographic profile of etched samples was studied by both scanning force and scanning electron microscopy.
I. INTRODUCTION
The future development of superior nonlinear optical (NLO) media is likely to depend more upon the utilization of tailoring techniques in well-known materials than upon the discovery of brand new materials. LiNbO3 (LN) is a ferroelectric material, which plays an important role in nonlinear optics and electro-optics because of its large second order nonlinearities. Only two possible domain orientations are allowed in lithium niobate (LN) crystals. The distinctly oriented domains differ in the sign of all nonvanishing components of the nonlinear optical tensor 2). Hence it is crucial to control the domain structure of the crystals for any nonlinear optical application. Birefringent phase-matching frequency conversion devices usually require single-domain crystals.1 In recent years much interest has been attracted by LN crystals with a periodic domain structure (PPLN), mainly for the effect known as quasi-phase-matched frequency conversion.2 The technique of quasi-phase-matching (QPM) a)
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J. Mater. Res., Vol. 15, No. 12, Dec 2000 Downloaded: 23 Apr 2015
opens a very attractive trend of possibilities in nonlinear optics; theoretically, any nonlinear interaction of waves within the transparency region of the crystal can be noncritically phase-matched at room temperature if the appropriate domain periodicity is provided. Among its advantages over single domain LN are (i) the possibility of involving the highest valued component d33 of the second order nonlinear tensor in the quasi-phasematched wave mixing processes, and (ii) the extension to wavelengths that are not phase matchable by birefringence. Additionally a reduction of photorefractive damage without the need for codoping with oxides like MgO or ZnO h
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