Laser Heated Pedestal Growth Technique Research Articles

Real time observation of domain reversal in cerium-doped Sr0.61Ba0.39Nb2O6 single crystal fibers

Domain configuration is of significant importance in utilizing ferroelectric single crystals such as strontium barium niobate (SBN) to design optoelectronic and nonlinear optical devices. This letter reports the real time observation of domain reversal in cerium doped SBN crystal fibers by electro-optic imaging microscopy. The SBN single crystal fibers studied were grown using the laser heated pedestal growth technique. The dynamic polarization switching behavior of SBN crystal fibers can be described as an antiparallel domain nucleation at low electric fields after a dormant period and a sideways growth of domain walls at higher electric field. These two different mechanisms result in the asymmetric current curve of domain switching dynamics.

Effect of the pulling rate on the quality of cerium-substituted YIG single-crystal fibers by LHPG

CeO 2 was added into yttrium iron garnet materials (YIG). Samples with a nominal composition of Y 3− x Ce x Fe 5O 12 (Ce:YIG), with x=0–0.4, were grown in air by the laser-heated pedestal growth technique. It is well known that it is difficult to grow pure YIG single-crystal fibers, due to the oscillatory instability of the melt and to the incongruent melting of the compound. In this work CeO 2 was added during the growth of YIG, which caused the composition and the flow in the melt to change. The growth conditions for producing good-quality Ce:YIG single crystal needs to be suitably adjusted in comparison with YIG growth. In the experimental results, it can be seen that the addition of CeO 2 into YIG increases the period of the oscillatory flow in the melt. Moreover, the greater the amount of CeO 2 added, slower is the pulling rate needed to grow good-quality single-crystal fibers. When a faster pulling rate is used to grow Ce:YIG material, more significant amount of foreign phases and cellular structures will form in the core region than in the peripheral region of the grown crystal fibers. This is thought to be due to the fact that the solute concentration and the experimental segregation coefficient along the convex shape of the growth interface in the melt were non-uniform.

Advances in growth of fiber crystal by the LHPG technique. Application to the optimization of Yb 3+-doped CaF 2 laser crystals

The laser heated pedestal growth (LHPG) technique is suitable to grow crystalline fibers and has been successfully applied for the general study of a lot of optical materials as laser crystals. Our general approach on the research of diode-pumped Yb 3+-doped host crystals is presented through typical example of CaF 2 fluoride, which is considered among the important laser crystals either for basic or applied reasons. Spectroscopic characterizations were carried out. Especially, Yb 3+ ( 2F 5/2) excited level experimental decay time dependence on Yb 3+ ion concentration is analyzed by using our own approach on the synthesis of a concentration gradient fiber grown in the laboratory. Our main objective is to contribute to have a better understanding of concentration quenching mechanisms not only in laser crystals but more generally in luminescent materials.

Transparent and inclusion-free RE 1−xLa xVO 4 (RE=Gd, Y) single crystal fibers grown by LHPG technique

We describe in this work the growth of pure and Nd-doped transparent fibers of RE 1− x La x VO 4 (RE=Gd, Y and x = 0.2 , 0.4 and 1.0) by the laser heated pedestal growth technique. The fibers obtained were in the range of 400–700 μm in diameter and up to 40 mm in length. Our crystalline fibers were free of black phases and microscopic inclusions. Temperature measurements on the molten zone surface showed that the liquid temperature suddenly dropped approximately 200 °C. This decrease in the liquid temperature is here associated with an self-adjustment of the melt composition during the fiber growth. Crystallographic data shows that the obtained fibers ( x = 0.2 and 0.4) belong to the I4 1/amd symmetry, with the exception of LaVO 4 ( x = 1.0 ), which crystallized with P2 1/n symmetry. Optical absorption and lifetime measurements on Nd-doped fibers showed the same good optical properties as the Nd:YVO 4 bulk crystals, with larger spectral linewidths which are desired for diode laser pumping.

One-Dimensional Crystal Growth Near Morphotropic Phase Boundary (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 Crystal Fibers

Ferroelectric perovskite (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals of near morphotropic phase boundary composition in rhombohedral phase, were successfully grown by a laser heated pedestal growth (LHPG) technique. The LHPG technique is a novel one-dimensional crystal growth method that requires no crucible for growth, allows compositions gradient adjustment during growth, and of high growth speed. The growth of highly volatile Pb-containing perovskite crystals was accomplished by an approach that uses excess PbO and boron oxide in the feed material that act as traveling flux in the molten zone during the growth. Controlling of growth orientation and composition homogeneity was studied. Dielectric, ferroelectric and piezoelectric properties of LHPG grown PMN-PT crystals were obtained and reported in this paper.

1.8μm emission and excited state absorption in LHPG grown Gd0.8La0.2VO4:Tm3+ single crystal fibers for miniature lasers

Abstract This work presents the characterization of high optical quality Gd0.8La0.2VO4:Tm3+ single crystal fibers grown by the low cost laser heated pedestal growth technique. The 400 μm diameter fibers were grown completely free from inclusions, without the need of O2 atmosphere. Their structural and spectroscopic characteristics are very similar to those of GdVO4:Tm3+, with the advantageous inhomogeneous broadening that eliminates the need of temperature control of the diode pumping laser for excitation at 0.8 μm. ESA transitions do not affect the population in level 3F4 significantly, and intense emission is observed at 1.8 μm. On the other hand, the 1.45 μm emission is deeply affected by ESA, while pumped at 0.8 μm excitation. The lower cost and easier growth of compact, excellent optical quality single crystal fibers, as compared to GdVO4:Tm3+ bulk crystals, indicates the fibers are interesting candidates for the construction of miniature lasers in the eye-safe spectral region (1.5–2.0 μm).

Stimulated emission and excited state absorption in neodymium-doped CaNb2O6 single crystal fibers grown by the LHPG technique

This work presents the structural and spectroscopic characterization of undoped and neodymium doped CaNb2O6 single crystal fibers grown by the low cost and versatile Laser Heated Pedestal Growth technique. To evaluate the potentialities of doped fibers, polarized absorption (σGSA,max809nm = 5.85×10−20cm2 with FWHM = 18 nm), luminescence and lifetime (τexp = 145 μs) measurements were taken, and radiative properties were also assessed by the Judd–Ofelt approach. The gain (σSE−σESA) spectrum was measured using the pump-probe technique and stimulated emission was observed at 1.064 μm with (σSE, max1.064 μm = 7.2× 10−20 cm2 and FWHM = 12 nm). The results are comparable to those of other well known niobate bulk laser crystals, but the easier, cheaper and faster growth of compact CaNb2O6:Nd3+ single crystal fibers makes them more attractive media for compact optical devices, such as diode laser pumped miniature lasers in the near infrared region.

Growth and X-ray characterization of Gd xYb 1−xTaO 4 ( [formula omitted]) single crystals with large lattice spacing gradient

Gradient single crystal fibers of GdTaO 4–YbTaO 4 have been grown by laser-heated pedestal growth (LHPG). The crystals of the compounds have differences in the lattice parameters of Δ a / a av = 2.5 % , Δ b / b av = 2.2 % and Δ c / c av = 0.9 % . The crystals obtained exhibit an optimum linear distribution of the compounds along the fiber axis and a lattice spacing gradient value of 2.91%/cm for ( 6 4 ¯ 0 ) reflection, the largest value of lattice spacing gradient reported up to this moment. The compositional and structural analysis shows that the LHPG technique and the GdTaO 4–YbTaO 4 system are very promising for obtaining good quality gradient crystals with large lattice parameters gradient.

Eu 3+ addition effect on the stability and crystallinity of fiber single crystal and nano-structured Y 2O 3 oxide

Nano-structured powders and fiber single crystals of cubic yttrium oxide undoped and Eu 2O 3 doped with luminescent properties were prepared using two techniques. The first one is focused on direct oxide precipitation at low temperature in which europium-doped yttrium oxide (Y 2O 3:Eu 3+) particles sizes less than 5 nm were synthesized in colloidal solution, followed by a controlled precipitation to obtain fine sub-micrometric powders. The second method is based on fiber single crystal growth using laser-heated pedestal growth (LHPG) and CO 2 laser beam as heating source at 10.6 μm and homogeneous starting rod materials obtained from the synthesis of nano-scale materials. The fibers grown by LHPG technique were single crystal, transparent, homogeneous, red color when Eu 3+ concentration is high. The crystal fiber quality decreases with increasing Eu 3+ concentration higher than 2% because of segregation problem. The materials obtained by the soft chemistry are cubic and lies in the nano-meter range. The purity of the materials, europium concentration limit, particles sizes and structure were obtained from X-ray powders diffraction at room temperature. The segregation coefficient of Eu 3+ is measured from EPMA analysis. The morphology of the materials was obtained using SEM. The luminescence of Eu 3+ has been detected by excitation at λ = 254 nm .

Laser-heated pedestal growth of colorless [formula omitted] single crystal fiber

We present a methodology that allowed us to prepare 400– 800 μ m diameter, 3 cm long colorless and transparent LaAlO 3 single crystal fibers by the laser-heated pedestal growth technique. This technique consists of growing LaAlO 3 fibers from pedestals prepared with a mixture of appropriate amounts of metal oxides without a prior chemical reaction. We also show that the use of prereacted and annealed pedestals produces dark fibers. LaAlO 3 fibers prepared from different La/Al ratio were studied. Pedestals with La / Al ⩽ 1 resulted in fibers with Al rich-phase microscopic inclusions. Fibers grown from La / Al > 1 were colorless, inclusion-free and transparent throughout their entire length. We also obtained transparent LaAlO 3 fibers from prereacted and high-temperature (1400 °C) annealed pedestals, although the fibers were brownish in color. The fiber/pedestal pulling ratio ranged from 0.9 to 1.1. The fiber growth direction was 〈 1 1 ¯ 1 ¯ 〉 . The crystal structure symmetry obtained for LaAlO 3 was R 3 ¯ c with a cell parameter of a = b = 5.368 ( 3 ) Å and c = 13.12 ( 4 ) Å . Optical and electron microscopy were used to characterize the fibers and the crystal/liquid interface.

Growth and structural characterization of M-type GdTaO4 single crystal fiber

The laser heated pedestal growth technique was used to obtain single crystal fiber of M-type GdTaO4. The fibers were around 3cm long, ∅0.8mm, transparent, colorless and did not exhibit any inclusions. The structural quality of the fibers was evaluated by X-ray rocking curve profiles and X-ray topography. Better quality crystals were grown perpendicular to (010) direction presenting rocking curve FWHM typically around 52arcsec for the (32¯3) reflection. The results confirm that good structural fibers can be successfully obtained by the procedure presented here.

Study of floating zone profiles in materials grown by the laser‐heated pedestal growth technique under isostatic atmosphere

AbstractThe analysis of the melt profile in floating zone techniques has been made in the past years by raising differential equations in terms of Cartesian coordinates and numerically looking for its solution. Although this method permits to establish quite good approximations to the real melt profile, the solutions are deficient in the prediction of new information that can be related to the thermophysical properties of most materials. We investigated the applicability of a different approach that starting from a novel differential equation permits its fitting to the profile of a real situation and also the determination of some important growth parameters like the range of shape stability. Results concerning melt profiles of materials grown under controlled atmosphere are reported. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and spectroscopic characteristics of neodymium dopedCaTa2O6 single crystal fibres grown by the laser heated pedestal growth technique

We report the successful growth of undoped and neodymium dopedCaTa2O6 single crystal fibres by the laser heated pedestal growth (LHPG) technique,as well as the fibres’ structural and spectroscopic characterizations. The700 µm diameter and 3 cm length fibres present high optical quality and excellent transparency, andx-ray diffraction measurements indicate that they crystallize in the cubic structure(Pm3). The extensive transmission window of the host crystal fibres enables the study of rare-earthion emission in the near-infrared region with several technological applications. Neodymiumdoped fibres (0.5–2.5 mol%) were characterized by ground and excited state absorptions,luminescence and lifetime measurements. Stimulated emissions were measured at1.06 µm ( transition) and around 1.34 µm (). Because CaTa2O6:Nd3+ fibres can be grown with excellent optical quality at low cost and in processes that aremuch faster than those usually used to grow bulk crystals, they might become aninteresting material for the construction of compact optical devices such as diode pumpedminiature lasers.

Laser heated pedestal growth and optical characterization of CaTa2O6 single crystal fiber

Transparent, colorless 30 mm long, (705±11) μm diameter CaTa2O6 single crystal fibers with a cubic crystalline structure (Pm3) were grown by the Laser Heated Pedestal Growth technique. The lattice parameter was a=(7.757±0.002) Å obtained from the Rietveld refinement. The fiber growth direction was determined as [101̄] by X-ray diffraction. The growth temperature was (2040±100)°C and the axial temperature gradient measured at the crystallization interface was (7.5±1.0)×103 °C/cm. The fiber/pedestal-pulling ratio was equal to 1.20. Undoped samples were characterized by optical microscopy, X-ray diffraction patterns, infrared transmission and Raman scattering. The structural and spectroscopic results indicate that this crystal may have potential as a host for active ions such as neodymium and erbium which have interesting emissions in the near-infrared region.

Correlation of the structure and the luminescence properties of Eu 3+-doped Gd 2O 3 oxide between fiber single crystal and the nano-size powders

Gd 2− x Eu x O 3 powder materials doped with Eu 3+ using different concentration from x=0 to 2 were prepared by a new sol-lyophilization synthesis and fiber single crystal (Gd 2O 3–Gd 2O 3/Eu 3+) oxides were grown using laser-heated pedestal growth (LHPG) technique. X-ray powder diffraction performed at room temperature showed that the materials obtained by lyophilization technique are cubic, lies in the nanometer range and different from bulk materials. The materials are a continued solid solution and the lattice parameter a-axis increases with Eu 3+ concentration. The fibers grown by LHPG technique were single crystal, transparent, red in color when Eu 3+ concentration is high, and the structure is monoclinic for Eu 3+<15%. The luminescence of Eu 3+ from C 2 crystallographic site was been detected. In the case of nano-particles oxide, an additional peak in emission spectral is obtained at λ=610 nm. The influence of Eu 3+, particles sizes and the structure on the luminescence spectral of Eu 3+ ions was been described.

Croissance de fibres polycristallines de composition eutectique AI2O3/Y3AI5O12 pour renforcement de composite

Eutectic fiber belongs to the Y 2 O 3 -Al 2 O 3 system were grown using Laser Heated Pedestal growth technique. We have controlled the fiber and diameter shape during the growth process. The interface of the melting zone was been plane. The fibers length was about few centimetre and are cracks and defects free. The eutectic fibers have high temperature strength properties, it was 577 MPa at 1500°C.

Nb2O5-Based Oxide Ceramics and Single Crystals-Investigation of Dielectric Properties

The behavior of enhancements of dielectric constant of Nb2O5 through small substituents of TiO2 is of interest. The ceramics of these solid solutions were prepared by the conventional mixed oxide method. Single crystal fibers were grown by the Lase r-Heated Pedestal Growth (LHPG) technique, which is considered to be a powerful tool for rapid growth of high-melting temperature oxides and incongruent melting compositions. The dielectric properties as function of temperature (−180°C to 180°C) and frequency (1 KHz to 1 MHz) were measured. The direct-current (dc) electric field dependence of the dielectric constant has been studied. The results show the strong dielectric dispersion which exists in a large frequency range which implies that the relaxation process involved is not of a Debye type. A relaxation distribution can be therefore expected. The influence of the cluster size dispersion is one assumption. Thus, the data of dc bias field dependence of the dielectric constant has been analyzed by the modified Devonshire relation including a cluster term giving the fitted parameters: cluster sizes distribution and their polar cluster polarization. aOn leave from the Petroleum and Petrochemical College, Chulalongkorn University, Thailand.

Nb 2O 5-based oxide ceramics and single crystals-investigation of dielectric properties

The behavior of enhancements of dielectric constant of Nb 2O 5 through small substituents of TiO 2 is of interest. The ceramics of these solid solutions were prepared by the conventional mixed oxide method. Single crystal fibers were grown by the Laser-Heated Pedestal Growth (LHPG) technique, which is considered to be a powerful tool for rapid growth of high-melting temperature oxides and incongruent melting compositions. The dielectric properties as function of temperature (−180 to 180 °C) and frequency (1 kHz to 1 MHz) were measured. The direct-current (dc) electric field dependence of the dielectric constant was also studied. The results show that a strong dielectric dispersion exists in a large frequency range, which implies that the relaxation process involved is not of a Debye-type. Relaxation dispersion was estimated by examining the influence of the cluster size distribution. The modified Devenshire relation including a cluster term was used to analyze data of dc bias field dependence of the dielectric constant, which gives the fitted parameters corresponding to cluster size distribution and their polar cluster polarization.

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.

Growth and characterization of columbite CaNb 2O 6 high quality single crystal fiber

High optical and structural quality columbite CaNb 2O 6 single crystal was grown by laser-heated pedestal growth (LHPG) technique directly from starting reagents. The structural quality of the fibers was evaluated by X-ray rocking curve profile, X-ray phase contrast radiography and X-ray topography measurements whereas optical quality was characterized by optical microscopy and infrared to visible transmission measurements. Raman shifting and structural refinement of X-ray powder diffraction were used to check the formation of single phase CaNb 2O 6. All results indicate that single phase, crack-free, colorless and transparent CaNb 2O 6 single crystal fiber was successfully obtained.