Tesfaye Gebre

Pyroelectric Properties of Pure and Doped Lithium Niobate Crystals for Infrared Sensors

The present study is an attempt to quantify and assess the effects of different dopants such as Fe, Fe/Mn and Eu on the growth, dielectric and pyroelectric properties of lithium niobate single crystals. Investigations reveal that Lithium niobate crystals, when doped with Fe ions, exhibits higher material figures of merit, for using in pyroelectric infrared sensing devices and vidicons applications with wider operating temperature range, as compared to other available pyroelectric crystals.

Growth and characteristics of organic and semiorganic nonlinear optical crystals

The growth, synthesis and characteristics of a new organic nonlinear optical crystal, a derivative of Schiff base compounds, 4-nitrobenzylidene-4-chloroaniline are reported. Good-quality crystals have been successfully grown using Bridgman-Stockbarger (BS) Technique. The organic crystal, 4-nitrobenzylidene-4-chloroaniline, shows good second harmonic generation of 1.064 micron wavelength. A recent work done on the semiorganic nonlinear crystals are reviewed along with results of growth of a few L-arginine phosphate type crystals is presented.

Growth of nonlinear optical materials at Alabama A&M University

Photonics/laser related technologies and applications rely on a steady supply of device quality single crystals. For more than a decade, the main focus has been on high performance nonlinear optical materials that comply with device manufacturing and end-use conditions such as high performance, high thermal, mechanical and chemical stability. To this end a variety of organic and semi-organic NLO materials have been successfully synthesized, purified and grown into bulk single crystals. In the process of growing bulk single crystals, various novel techniques and processes have been developed. In this presentation, results of synthesis and crystal growth processing of the various NLO materials such as methyl-(2,4-dinitrophenyl)-aminopropionate: 2-methyl-4-nitroaniline (MAP:MNA), L-arginine phosphate, L-Histidine tetrafluoroborate, L-arginie tetrafluoroborate and other isomorphs, pure and doped Bismuth silicon oxide, pure and doped Lithium niobate crystals will be discussed including challenges faced, novel techniques and experimental set-ups developed in growing large high quality crystals.

Electrooptic characterization and Czochralski growth technique of pure and doped lithium niobate crystals

Ferroelectric Lithium Niobate (LN) possesses a combination of unique electrooptic, piezoelectric, pyroelectric, and photorefractive properties. These features make it suitable for applications in optical devices-as modulators, switches, and filters in communication systems and holographic recording medium, etc. Here, the growth of lithium Niobate doped with iron and doubly doped with iron and manganese ions will be described. The growth technique will be through Automatic Diameter Control Czochralski Design. From these grown crystals, critical electrooptical coefficients using null detection polarimetry are provided. The results of growth, electrooptic measurements, and some physical properties are compared and presented. Also, the use of doped LN crystals in devices is discussed.

Growth and Characteristics of Single Crystals of Lithium Niobate

Lithium niobate single crystal is an excellent material for various optical applications such as frequency conversion, optical switches, optical modulators and others. An automatic diameter control Czochralski crystals growth system has been designed and fabricated. A brief description of the entire system along with software developed has been described. With optimized growth parameters, pure and Fe/Mn doped crystals have been successfully grown using this system. Preliminary characterizations of these crystals have also been presented.

Growth and optical characteristics of pure and doped lithium niobate crystals

The growth of lithium niobate doped with iron and doubly doped with Iron and Manganese ions with optimum growth parameters by using automatic diameter control Czochralski system designed is briefly described. The results of investigation of optical and some physical properties of these crystals are presented and compared with pure LN crystals.

Synthesis, characterization, and bulk crystal growth of nonlinear 3-substituted salicylidene aniline derivatives

Salicylidene-aniline (SA) derivatives have been synthesized and characterized for optical and nonlinear optical properties. The substituents used as methyl (-CH3), chloro (-Cl), and nitro (-NO2) groups. These substituent groups show a variation in their electro-negativity characteristics and hence have the capacity to perturb the electrons system in the parent ring structure of the salicylidene-aniline compound. Material characterization has been done using various analytical tools namely: DSC, FTIR, UV-VIS and GC/MS. The nonlinear optical characterization has been done using the Kurtz powder efficiency method. The nonlinear refractive index and the third order susceptibility have been determined using the Z-Scan method in solution using ethanol as the solvent. The Kurtz powder efficiency measurements using urea as standard gives the values as 0.7 for 3-Cl SA, 0.8 3-NO2 SA and 1.0 for the 3-CH3 SA derivative. The results of single bulk crystals grown using the Bridgman-Stockbarger method are reported.

Purification of organic nonlinear optical materials for bulk crystal growth from melt

The techniques developed for purification of nonlinear optical organic materials, such as benzil, 2-methyl-4-nitroaniline (MNA), Dicyanovinyl anisole (DIVA) and its derivatives, nitrophenyl prolinol (NPP) and other Schiffs base compounds, include Kugelrohy method, physical vapor transport, zone refining and recrystallization from the solvent are described. Purity of the materials is tested using differential thermal analysis, gas chromatograph/Mass detector, Fourier Transform Infrared spectroscopy and melting point measurements. The purified materials were later used in the growth of single crystal by Bridgman-Stockbarger and Czochralski techniques.