J.P. Andreeta

Differential interferometric technique for the measurement of the nonlinear index of refraction of ruby and GdAlO3:Cr+3.

A differential interferometric method for direct measurements of the real part of the nonlinear index of refraction n2 has been developed. With this method we were able to measure n2 as low as 10−10 cm2/W. This method was used to measure n2 in both ruby and GdAlO3:Cr+3 for the first time. Our results show that the real part of n2 in ruby is an order of magnitude larger than the imaginary part. This result clarifies the controversy about the dispersive or absorptive origin of the phase conjugation in ruby- and cromium-doped crystals.

Growth and characterization of crack-free scheelite calcium molybdate single crystal fiber

High-optical and structural quality single-phase scheelite calcium molybdate (CaMoO 4 ) single crystal was grown by the floating zone-like technique named laser-heated pedestal growth. The optical quality of the as-grown crystal was characterized by optical microscopy and absorption measurements, whereas the structural quality was evaluated by X-ray rocking curve profile, X-ray phase contrast radiography and X-ray topography measurements. The structural refinement of X-ray powder diffraction data recorded from crushed crystals was used to check the formation of single phase CaMoO 4 . All the obtained results indicate that completely crack-free, single phase, clear and transparent CaMoO 4 crystal was grown.

Growth of single-crystal photorefractive fibers of Bi12SiO20 and Bi12TiO20 by the laser-heated pedestal growth method

Abstract Photorefractive single-crystal fibers of Bi 12 SiO 20 up to 90 mm in length and Bi 12 TiO 20 up to 50 mm in length with diameters of 650–1200 μm were grown by the laser-heated pedestal growth (LHPG) method. Both Bi 12 SiO 20 and Bi 12 TiO 20 fibers were pulled from stoichiometric (6:1) melts at pulling rates of 0.3 and 0.2 mm/min, respectively, the feeding rate was 0.1 mm/min. Growth conditions, morphology and chemical composition of the grown fibers were studied. The possible mechanisms of crystallization of incongruently melting Bi 12 TiO 20 fiber from the stoichiometric melt were discussed. The energy-exchange effect was observed in the BSO fibers at the wavelength λ = 0.5145 μm .

Improved laser-heated pedestal growth system for crystal growth in medium and high isostatic pressure environment

A modified apparatus for single-crystal-fiber growth in an isostatic gaseous environment and for a large range of pressure (100 mbar up to 100 bar) using a floating-zone-type method known as laser-heated pedestal growth is described. The difficulties and advantages of its design are discussed through examples of crystal growth of some oxide materials.

Magnetocaloric effect of La0.8Sr0.2MnO3 compound under pressure

The La0.8Sr0.2MnO3 compound presents a ferromagnetic paramagnetic transition around room temperature to which a reasonably high magnetocaloric effect is associated, turning this material of interest for application in magnetic refrigeration. We synthesized this compound in fiber single crystalline form by the Laser Heated Pedestal Growth method. The sample was characterized by x-ray diffraction and magnetic measurements as a single phase and with the required magnetic properties. We measured the magnetic properties and the magnetocaloric effect under hydrostatic pressure for pressures up to 6 kbar as a function of temperature. Our results indicate that the Curie temperature increases with pressure while the low temperature transition from the orthorhombic to the rhombhoedral structures decreases as pressure increases. This is in close agreement with the literature. Measurement of the magnetocaloric effect at the high temperature transition indicates that the peak of the effect follows the trend of the Cur...

Excited-state absorption and 1064-nm end-pumped laser emission of Nd:YVO4 single-crystal fiber grown by laser-heated pedestal growth.

We present an investigation of the excited-state absorption and laser emission of a 1.0-at. %-Nd3+-doped YVO4 single-crystal fiber grown by the low-cost and versatile laser-heated pedestal growth technique. Efficient laser emission at 1064 nm was achieved when the fiber was pumped, in an end-pump cavity, by a Ti:sapphire laser at 808 nm. A continuous-wave threshold of 10 mW was observed with an efficiency of 42% with respect to the absorbed pump power and the maximum output power of 200 mW. These results are excellent when compared with those of a commercial bulk crystal adapted to the same cavity (48% efficiency, 250-mW maximum output power). Thus the fibers are characterized as strong candidates for the construction of compact lasers that can also be pumped by low-cost diode lasers.

Optical properties of Nd3+-doped Ca3(VO4)2 single crystal fiber

Abstract Optical absorption and photoluminescence of Ca 3 (VO 4 ) 2 single crystal grown by a floating-zone technique and containing Nd 3+ ions were investigated. High absorption coefficients and broadening of most absorption bands are present at 300 K, while substructures in some of the same bands can be evidenced at 12 K. Most features of measured spectra are characteristic of random occupation of more than a single Ca 2+ site by the Nd 3+ ion and of distortions provoked by different charge compensation mechanisms involving oxygen vacancies promotion in the crystal lattice. Nd 3+ optical properties were studied by using the Judd-Ofelt theory to calculate the spectral parameters relevant for laser applications.

Single-crystal SrTiO3 fiber grown by laser heated pedestal growth method: influence of ceramic feed rod preparation in fiber quality

The rapidly spreading use of optical fiber as a transmission medium has created an interest in fiber-compatible optical devices and methods for growing them, such as the Laser Heated Pedestal Growth (LHPG). This paper reports on the influence of the ceramic feed rod treatment on fiber quality and optimization of ceramic pedestal processing that allows improvements to be made on the final quality in a simple manner. Using the LHPG technique, transparent crack-free colorless single crystal fibers of SrTiO3 (0.50 mm in diameter and 30-40 mm in length) were grown directly from green-body feed rods, without using external oxygen atmosphere.

Growth of yttrium orthovanadate by LHPG in isostatic oxygen atmosphere

Abstract The growth of undoped and Nd 3+ -doped YVO 4 crystals in isostatic oxygen atmosphere by the laser-heated pedestal growth technique was investigated. Absorption, photoluminescence, X-ray powder diffraction and Raman shift spectra were used to characterize the grown crystals. Differences in Y–V and oxygen stoichiometries were identified and discussed in terms of the starting materials processing, crystal growth dynamics and post-growth thermal treatment. The experimental results indicate that single crystal fibers with general optical and spectroscopic properties close to those of the best respective available bulk single crystals were grown.

The influence of temperature gradients on structural perfection of single-crystal sillenite fibers grown by the LHPG method

Abstract Single-crysta fibers of Bi 12 SiO 20 and Bi 12 TiO 20 up to 90 mm in length with diameters of 200–1200 μm were pulled along the 〈001〉 and 〈011〉 crystallographic axis by the LHPG method. The powder X-ray diffraction and the electron-probe microanalysis were used for characterization of the grown fibers. The microstructure of sillenite fibers was studied by the chemical etching method. The dislocations, inclusions and striations are the main imperfections that were found in the fibers. The dislocation density equal to 1×10 5 pits/cm 2 was estimated on the ground of the etching pits using optical and electronic microscopy and was compared to that evaluated by the Tsivinskiis relation based on the axial temperature distribution in the fiber and on the elastic properties of the material. The conditions of the formation of microdefects are discussed in relation with the growth conditions, morphology and chemical composition of the grown fibers.