Mechanisms of Formation of Nonlinear Optical Light Guide Structures in Metal Cluster Composites Produced by Ion Beam Imp
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* Department of Natural and Physical Sciences, Alabama A&M University, 4900 Meridian Drive, Normal, AL 35762, [email protected] ** Center for Irradiation of Materials, Alabama A&M University, 4900 Meridian Drive, Normal, AL 35762 *** Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 ABSTRACT We report the results of characterization of linear and nonlinear optical properties of a light guide structure produced by MeV Ag ion implantation of LiNbO 3 crystal (z-cut) in relation to the mechanisms of formation. INTRODUCTION Ion implantation has been shown to produce a high density of metal colloids in glasses and crystalline materials. The high-precipitate volume fraction and small size of metal nanoclusters formed leads to values for the third-order susceptibility much greater than those for metal doped solids [1]. This has stimulated interest in use of ion implantation to make nonlinear optical materials. On the other side, LiNbO 3 has proved to be a good material for optical waveguides produced by MeV ion implantation [2]. Light confinement in these waveguides is produced by refractive index step difference between the implanted region and the bulk material. Implantation of LiNbO 3 with MeV metal ions can therefore result into nonlinear optical waveguide structures with great potential in a variety of device applications. We describe linear and nonlinear optical properties of a waveguide structure in LiNbO 3-based composite material produced by silver ion implantation in connection with mechanisms of its formation. EXPERIMENT The sample was made of 1-mm thick LiNbO 3 ( z-cut) implanted with 1.5-MeV Ag ions to a dose of 2.0x10 16 cm"2.2 Implantation was done at room temperature. Fig.1 presents the distribution of the implanted silver along the depth of the sample calculated by the Monte-Carlo simulation program TRIM96 [3]. The position of the peak of the distribution defines the depth of the implanted layer at 0.41 gm and FWHM of the distribution gives an estimate of 0.24 gim for the thickness of the layer. Light transmission along the implanted layer (treated at 5000C) was studied using the prism coupling technique [4]. The technique is based on light tunneling from a prism with high refractive index (rutile, index is 2.8643) to the implanted light guiding layer through a small air gap (Fig. 2). The phase matching condition for light coupling is np sin0m = Nm , (1) where np is the prism refractive index; 0 m is the angle of incidence; Nm is the propagation 357 Mat. Res. Soc. Symp. Proc. Vol. 504 © 1998 Materials Research Society
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Fig. 1. The concentration of the implanted Ag ions versus the depth of the LiNbO3 sample calculated by the 16 -2 Monte-Carlo method. The energy of the Ag ions is 1.5 MeV, the fluence is 2.OxlO1 cm.
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Fig. 2. Scheme of the prism coupling experiment.
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