Cynthia R. Ferrari

Spectral imaging for visualization of distribution of Nd3+ ions in CaTaO6 fibre

Knowledge of distribution (uniformity or otherwise) of dopant ions in a fibre is important, for it may affect the desirable optical properties of fibre. Here we describe our attempt to look at the distribution via an uncommon technique, i.e. spectral imaging. In this report we describe briefly the specimen preparation, relevant details of the instrumental setup and the results. Some remarks are included at the end to indicate the possible improvements and the quantitative analyses that can be easily implemented if needed. Introduction Single crystals containing rare-earth ions like Nd 3+ are routinely used as lasing medium in a diode laser pump system. The need for small foot-print and economic laser is still growing and the wavelength region around 1 micron has applications in the telecommunications industry, as a near infrared source in the medical diagnostics systems and also as a primary source to obtain visible region wavelengths by harmonic generation. Manufacturing of single crystals is an expensive venture compared to fibre-pulling especially when the geometry of the end use is a cylinder. Thus, single crystal production via laser melting is an attractive alternative. The effectiveness and the performance of lasing medium naturally would depend upon the spatial distribution of the lasing ion and the formation of clusters etc. within the lasing medium. We have successfully made CaTaO6 fibres doped with Nd 3+ ions by laser heated pedestal growth (LHPG) technique and here we describe our attempt to look at the cross section of the prepared fibre for the distribution of the fluorescent ions via spectral imaging. In the following, we first describe briefly the sample preparation, followed by a short description of a microscope modified for the purpose and then present the results. Experimental Details First we describe the method of making a single crystal fibre. Stochiometric amounts of reagents were appropriately mixed in a Polyvinyl Alcohol medium and the resulting paste was submitted to cold extrusion process. The method resulted in cylinders of approximately 1mm diameter and of lengths varying between 50mm and 60mm. The equipment for LHPZ was developed in house and employs CO2 laser of 10.6 micron wavelength and 125 W power. The liquid phase temperature as measured by an optical pyrometer was 1940 ±100oC. Average pulling rate was about 1.45 mm/mn for the seed and 1.20 mm/mn for the fibre. The doping levels in terms of molar percentage of Nd2O3 varied between 0.5 and 2.5 in the steps of 0.5. Laue X-ray photography was used to verify the single crystal nature of the fibre; the composition and the crystal structure were confirmed by X-ray diffractogram of a piece of the fibre crushed into powder. Fig.1 shows a picture of fibres with different doping levels. And, in the Fig. 2 we show the X-ray diffraction pattern of the undoped fibre taken on Rigaku Rotaflex equipment. Rietveld method of refining crystal parameters was used to verify that the fibre contained only single desired phase of CaTaO6. Materials Science Forum Online: 2004-05-15 ISSN: 1662-9752, Vols. 455-456, pp 665-670 doi:10.4028/www.scientific.net/MSF.455-456.665