Growth Of Crystal Fibers Research Articles

Dynamics of Er3+:YAG thermal radiation spectra near solid-melt interface at single crystal fiber growth process

The evolution of the Er3+:YAG thermal radiation spectra at heating up to the melting point was investigated in the visible range when growing a crystal fiber by the Laser-Heated Pedestal Growth (LHPG) method. The Er3+:YAG melt of about 1 mm thickness radiates like a black body in several spectral bands sometimes different from the crystal absorption lines. The real melt temperature in the middle of the growth zone was estimated as 2620 ± 15 K. The spectral profile of Er3+:YAG emissivity in the visible range for a melt layer of about L ≈ 1 mm at 2620 K is shown in the Figure.

Temperature and emissivity measurements at the sapphire single crystal fiber growth process

We present a new method for evaluation the absorption coefficient of the crystal melt around the phase transition zone for the spectral range of semitransparency. The emissivity distribution across the crystallization front of the sapphire crystal fiber was measured at the quasi-stationary laser heated pedestal growth (LHPG) process (Fejer et al., 1984; Feigelson, 1986) and the data for solid state, melt and phase transition zone (melt-solid interface) were obtained. The sapphire melt absorption coefficient was estimated to be 14 ± 2 cm−1 in the spectral range 1–1.4 μm around the melt point. It is consistent with data, obtained by different other methods. This method can be applied to determine the absorption coefficient for other materials.

Directional crystallization of polymer molecules through solvent annealing on a patterned substrate.

Multi-crystalline fibers of poly (3-hexylthiophene) (P3HT) have been grown on a patterned substrate through annealing the spin-coated film in the solvent of 1,5-pentanediol at 120 °C. The large-area patterns of photoresist grating have been fabricated by interference lithography, enabling growth of crystal fibers in a length scale of centimeters. The produced organic crystal fibers were characterized by microscopic, spectroscopic, and electrical conductivity performances. Mechanisms for the crystallization processes were investigated.

Growth and spectroscopic characterizations: properties of Nd:LiLa(MoO4)2single crystal fibers

In this work single crystal fiber growth by the micro-pulling-down technique and the structural and spectroscopic characterizations of undoped and Nd3+-doped double molybdate LiLa(MoO4)2 are reported. The optimization of the growth conditions was studied in order to avoid facet formation. The grown fibers are free of scattering centers and the real dopant concentrations were confirmed to be very close to the nominal ones with a quite uniform distribution along the fibers length. The crystallographic structure concerning the scheelite tetragonal symmetries was re-evaluated. Time-resolved fluorescence spectroscopy was applied to the evaluation of some optical properties. Selective laser excitation of the 4F3/2 at 875 nm and 4F5/2 at 805 nm has established that the energy levels above the 4F3/2 level are entirely quenched by multiphonon emission in Nd:LiLa(MoO4)2 crystal fiber. The potential laser gain of the system was determined using a numerical solution of the rate equations system for the 805 nm continuous pumping regime, which shows the maximum gain of the laser emission at 1.064 μm for using a Nd3+-doping of 5 mol%.

Growth and characterization of bismuth zinc borate Bi2ZnB2O7 crystal fibers by the micro-pulling down technique

Bi2ZnB2O7 (BZBO) is a new non-linear optical material with high potential applications. In this paper, we report on the preparation of BZBO powder and growth of crystal fibers by the micro-pulling down technique (μ-PD) for the first time. Several fibers with constant diameter between 300 and 550μm and length up to 100mm were pulled in air atmosphere with rates between 4.5 and 12mmh−1. Various physical and optical characterizations (optical microscopy, SEM, Raman micro-spectroscopy, and EDX microprobe) were performed to investigate the crystal quality and compositional homogeneity of the obtained fibers. The obtained fibers showed a uniform color from yellow to orange-red and a particular microstructure, presently attributed to the presence of disordered or glassy parts containing a Bi-rich compound.

Three-dimensional simulation and experiment on micro-floating zone of LHPG with asymmetrical perturbation

This is a combination of experiments and three-dimensional numerical simulation approach to verify the simulation results of the molten zone shape by experimental data. We study the effect of CO2 laser heating ring and gravity field deviation caused by the space perturbation on micro-floating zone of LHPG during the fiber growth on comparing similar conditions and changing the input parameters of simulation. Our preliminary results compared with the molten zone shape are satisfied. The shape of the molten zone (especially the solid–liquid interface) by the asymmetrical heating effect is much larger than the result by gravity field in the simulation, which results in tilting by 3° when the source rod diameter is below 500μm. The influence will decrease rapidly with the reduction of the source rod scale and diameter reduction ratio. These results will help us with the internal flow of the molten zone analysis and developing LHPG crystal fiber growth along the horizontal direction in future.

Low-loss propagation in Cr^4+:YAG double-clad crystal fiber fabricated by sapphire tube assisted CDLHPG technique

Cr4+:YAG double-clad crystal fiber with an uniform 10-microm core was fabricated by using a sapphire tube as a heat capacitor to stabilize the power fluctuation of the CO2 laser in the co-drawing laser-heated pedestal growth system. The uniformity of the fiber core showed a factor of 3 improvement compared to that without the use of sapphire tube. The variation of the core diameter is within the +/-1.35-degree adiabatic criterion and has a autocorrelation length of 1.7 mm. The measured propagation loss is only 0.02 dB/cm. The sapphire tube also reduces the vertical temperature gradient during the crystal fiber growth process so the 10-microm crystal core exhibits a smooth perimeter. The sapphire tube assisted system can be applied to the growth of many other optical crystal materials.

Nd : YVO 4 single crystal fiber growth by the LHPG method

Nd : YVO 4 single-crystal fibers of various compositions were grown by the laser-heated pedestal growth (LHPG) method. During the crystal growth, a thermal imaging radiometer was used to observe the thermal radiation emitted by the melt, ceramics and crystals. Parameters of the LHPG method, such as powder compositions, ceramic process, and crystal-growth conditions are discussed. With the higher pulling rates during the LHPG process and proper ceramics-production control, the decomposition of V 2O 5 could be reduced and a-axis Nd : YVO 4 crystal fibers were grown. Lattice constants of the grown crystal fibers were measured.

Barium sodium niobate single crystal fiber growth by the micro-pulling down (μ-PD) technique

Growth of single crystal fibers from the congruently melting composition of barium sodium niobate Ba 2.065Na 0.81Nb 5.01O 15 melt using a micro-pulling-down system has been demonstrated. This method avoids some problems associated with conventional melt techniques such as the Czochralski method. Neither cracks nor any other kind of inhomogeneity could be detected in the crystals, which are therefore suitable for nonlinear optical applications. Results of coupled differential thermal and thermogravimetric analysis indicated that the melting point of the starting mixture was 1453°C. No phase transitions other than melting and solidification were detected.

Interface field-modified solute partitioning during Mn : LiNbO 3 crystal fiber growth by micro-pulling down method II Radial distribution analysis

The influence of an interface electric field on the solute partitioning during LiNbO 3 single crystal fiber by micro-pulling-down method has been studied. Thermoelectric power was a dominant cause of the electric field, and the Seebeck-effect-induced electric field was measured in the solid near the interface along the axial as well as radial directions. Solute partitioning was subject to these interface field effects. Mn was rich in the core of the Mn-doped LiNbO 3 crystal fiber of small diameter, which was two dimensionally analyzed to predict the redistribution of the ionic solute by an interface electric field. The inversion of the radial temperature gradient in the molten zone was specific to the micro-pulling-down method and suppressed the radial thermoelectric power in the liquid, which consequently led to the rather homogeneous radial solute distribution in the solid.

Interface field-modified solute partitioning during Mn : LiNbO3 crystal fiber growth by micro-pulling down method. I. Axial distribution analysis

During the growth of Mn : LiNbO3 crystal fiber by the micro-pulling down method, the solute partitioning is greatly influenced by the interface electric field mainly caused by the large temperature gradient at the interface. This was experimentally and analytically studied for the initial transient, steady-state and terminal transient solute redistribution based on the concept of a field-modified partition coefficient, kE0, and an effective growth velocity, VEL. The field-modified effective partition coefficient, kE, becomes larger than unity in the steady state although its equilibrium partition coefficient, k0 < 1.0, which consequently leads to the Mn concentration deficiency in the solid during the terminal transient. There is a critical growth velocity, V∗, below which the effective growth velocity, VEL, and the field-modified equilibrium partition coefficient, kE0, take negative value in which cases the positive ions such as Mn4+ move away from the interface.

Anomalous segregation phenomena during LiNbO_3 crystal fiber growth by m-PD method

Anomalous segregation phenomena during LiNbO_3 crystal fiber growth by m-PD method

Preparation of BiSrCaCuO superconductors by laser floating zone melting technique

The growth of crystal fibers of BiSrCaCuO superconductors with different nominal compositions by the laser floating zone melting technique has been studied. The seeding and feeding rods for the process were prepared by common solid-state sintering. The crystals were grown with pulling rates and temperatures of the molten zones in the ranges of 0.17–10 mm/min and 900–950°C, respectively. The as-grown crystals were 0.5–1.5 mm in diameter and show high densities and aligned structures with the a-b planes parallel to the growth axis, which would be greatly helpful in reducing the weak links between grain boundaries and thus enhance transport critical current density. It was found that after a suitable post-heat-treatment (e.g. 860°C/10 h + furnace cooling), the samples with nominal composition BiSrCaCu 2O y , gave a superconducting transition temperature of 85 K ( T c, zero ) and a rather high transport critical current density of 1800 A/cm 2 at 77 K and zero field. These samples were also characterized by X-ray diffraction, optical and scanning electron microscopies and electron probe.