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J.J.?RomeroEmail author M.R.B.?Andreeta E.R.M.?Andreeta L.E.?Bausá A.C.?Hernandes J.?García Solé 《Applied Physics A: Materials Science & Processing》2004,78(7):1037-1042
The growth from ceramic pedestals of single crystal fibers of strontium barium niobate (SBN), doped with different Nd concentrations, was studied. High-quality fibers were grown for Nd doping levels of up to 4.2 at.%, and doping levels as high as 9.9 at.% were reached. No signs of core effects were observed, even for the highest concentration samples. The emission spectra of Nd3+ ions in the fibers did not differ from those obtained from bulk SBN crystals, showing very broad bands due to the typical disorder of the crystallographic tungsten-bronze structure. Fluorescence quenching was clearly observed for Nd doping levels above 2 at.%. PACS 81.10.Fq; 78.55.-m 相似文献
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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. 相似文献
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V. V. Prokofiev J. F. Carvalho J. P. Andreeta N. J. H. Gallo A. C. Hernandes J. Frejlich A. A. Freschi P. M. Garcia J. Maracaiba A. A. Kamshilin T. Jaaskelainen 《Crystal Research and Technology》1995,30(2):171-176
Photorefractive Bi12TiO20 single crystals of high optical quality were grown in a resistive heating furnace from high temperature nonstoichiometric (10:1) solutions of Bi2O3 and TiO2 at pulling rates 0.3–0.8 mm/h at rotation 20–30 rpm along the <001> and <011> axis. Powder X-ray analysis, Laue method, and electron-probe microanalysis were used for characterization. BTO crystals have the bcc structure of sillenite type with a0 = 10.178(8) Å. The chemical composition of the crystals can be written down as Bi12.1 ± 0.2Tio0.96 ± 0.09O20.1. Natural optical activity ρ of BTO crystals is 6.3 ± 0.2 deg/mm at λ = 0.633 μm and 11.9 ± 0.2 deg/mm at λ = 0.5145 μm, optical absorption coefficient α = 0.42 ± 0.04 cm−1 at λ = 0.633 μm and linear electro-optic coefficient r41 = r52 = r63 = 5.3 pm/V. Fanning effect in the “fiber-like” BTO sample was studied and double phase conjugation with conversion efficiency up to 8% was observed in a wide range of incidence angles of the pump at λ = 0.633 μm for 2 × 3 mW input light power. 相似文献
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J. Baszyński W. Kowalski C. A. Cardoso F. M. Araujo-Moreira M. R. B. Andreeta A. C. Hernandes 《Czechoslovak Journal of Physics》2004,54(4):39-42
The magnetic switching processes in mechanically controllable junctions (MCJ), made from high-quality single crystals of La0.7Sr0.3MnO3, are studied as a function of the DC current (up to 109 A/cm2) passing through the nanoconstriction. The current-voltage (I-V) curves of the MCJ are typical for an electron tunnelling process. By fitting I-V curves to the Simmons model, the barrier width (1 - 1.6) nm and height (0.4 - 1.7) eV of the junctions and their effective tunnel area (1-10) × 10?11 cm2 were estimated. Based on the close relation between transport properties and the magnetization in manganese compounds, we interpret the jumps in the conductance of MCJ, by integer multiples of e2/h, as due to the configuration reorientation of the magnetization of the Mn-ions clusters at the constriction surfaces. 相似文献
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Simple optical apparatus for trepanning and percussion microdrilling using pulsed green Nd:YAG laser
Laser microdrilling is becoming an important tool in a wide spectrum of industrial applications due to the possibility to
produce microholes in almost any type of materials. The purpose of this study was to create a simple and efficient optical
apparatus that could produce microdrillings by either percussion or trepanning methods. The developed system is composed by
a nanosecond Nd:YAG laser operating at 532 nm and one convergent lens with off-center optical axis of 1′. For the trepanning
method the lens spins in its geometrical center at constant angular speed of 350 rpm. Typical microholes diameters obtained
in metallic aluminum were in the range of 22 to 95 μm and 70 to 150 μm for the percussion and trepanning methods, respectively.
Typical drilling velocities were in the order of 10 μm/s for applied fluences ranging from 22 to 150 J/cm2 for both methods. The values of the ratio between input and output diameters were 0.30 and 0.25 for microholes obtained by
percussion and trepanning methods, respectively. The best microholes morphology was obtained using the trepanning method.
The results for both methods are discussed based on the optical and thermal properties of the material processed and the constructed
apparatus. 相似文献
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M. R. B. Andreeta A. C. Hernandes S. L. Cuffini J. A. Guevara Y. P. Mascarenhas 《Journal of Crystal Growth》1999,200(3-4):621-624
SrHfO3 single crystal fibers were grown by the laser heated pedestal growth technique. These fibers have orthorhombic symmetry with lattice parameters of a=5.773(1) Å, b=5.764(3) Å, c=8.157(2) Å at 300 K. 相似文献
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The structural and electronic transport properties of La1−x
Ce
x
MnO3 (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with
Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration
up to 50% doping. The system La0.5Ce0.5MnO3 also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition. 相似文献