Recently, a superconducting magnet has been used to obtain better quality protein crystals. It is possible to reduce effective gravity and damp natural convection by applying a vertical magnetic field gradient to cause an upward magnetization (Kelvin) force. When protein crystals (snake muscle fructose-1,6-bisphosphatase) were formed in 0.7-0.8 g, their resolutions of X-ray diffraction were improved by 30% compared with those formed outside the magnet. On the other hand, in a uniform field of 10 T which did not cause an upward force, the improvement of the quality of orthorhombic lysozyme crystals was found. In this paper, besides through the upward magnetization force, we studied how a strong magnetic field damps natural convection and influences the crystal quality. First, we discussed the damping of natural convection by Lorentz force, and concluded it almost negligible because Hartman number is about 3.5 for the typical protein crystal formation experiments. Second, we studied the magnetic effect on the viscosity of protein solutions and found that the viscosity increases under 10 T when the solution contains suspended small crystals. Numerical simulations showed that the viscosity increase causes the damping of natural convection during protein crystal growth. Furthermore, the effect of magnetic orientation of suspended crystals on the crystal quality was also discussed. These types of magnetic effect will occur both in gradient and uniform magnetic fields. If we use these kinds of magnetic effects efficiently, it will be possible to improve the crystal quality.
In order to understand the nature of surface patterns on silicon melt in industrial Czochralski furnaces, we conducted a series of unsteady three-dimensional numerical simulations of thermocapillary flow in thin silicon melt pools in annular containers under microgravity. The pool is heated from the outer cylindrical wall and cooled at the inner wall. Bottom and top surfaces either are adiabatic or allow heat transfer in the vertical direction. With large temperature difference in the radial direction, the simulation can predict two types of oscillatory convections. One is characterized by spoke patterns traveling in the azimuthal direction. The other one is characterized by radially extended roll cells periodically alternating the azimuthal flow directions but are stationary. The small vertical heat flux (3W/cm2) does not have significant effects on the characteristics of those oscillatory flows. Details of the flow and temperature disturbances are discussed and the critical conditions for the incipience of the oscillatory flow are determined.
Several very stable imine derivatives were synthesized by the reaction of aromatic aldehydes with diaminomaleonitrile. These compounds include different donor groups connected to the acceptor by conjugated chains of different lengths. Another group of compounds that have been synthesized is chiral pyrrolidine derivatives with varying acceptor substituents. After crystallization, products were characterized by X-ray analysis and other physical methods. Most of these materials crystallize in noncentrosymmetric space groups that define their second harmonic generation. The molecules have almost planar structures, that is favorable for the strong conjugation between donor and acceptor fragments, and take part in the formation of intermolecular hydrogen bonds. Quantum calculations of molecular electronic properties (dipole moments, hyperpolarizabilities of first and second order) have been completed.
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 Schiff's 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.
The crystallization of the N-4-nitrophenyl-L-prolinol (NPP) organic glass was investigated by differential scanning calorimetry (DSC). The results showed the influence of temperature and temporal treatment of the melt on the crystallization processes obtained while cooling from the liquid or d uring heating from the glass state. The behavior of the crystallization kinetics from the glass state was studied under both nonisothermal and isothermal conditions. On the first case, DSC thermograms were recorded at heating rates from 2 to 40oC/min. The crystallization temperature was found to depend on heating rates. Two crystallization phases have been found during the heating of the sample from the glass-like disordered states in the continuing cycling of DSC. In the second case, isothermal crystallization was observed at temperatures ranging between the glass transition and crystallization points.
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.
Crystalline polymorphism is quite common for nonlinear optical (NLO) compounds. During our studies of NLO materials we found several compounds that crystallize in two or more forms. We present a short review of our recent data on the crystalline polymorphism of NLO compounds. Among the compounds studied, we found examples of concomitant polymorphism, induced conformational polymorphism, and organic polytypism. For several compounds, X-ray data are discussed along with computational data on molecular and crystal structure energy.
Solid state lasers pumped with diode form a new class of lasers which replace those with lamp pumped lasers presently used. Properties of most often discussed single crystals for diode pumped solid state lasers are presented. YAG crystals doped with Yb and double-doped with Er, Yb and YVO crystals doped with rare earth elements are discussed. Recently promising for laser application seems to be doped tungstate KGd(WO4)2 and KY(WO4)2 crystals. Relatively new group of laser materials are borates, like GdCa4(BO3)3, Ca4YO(BO3)3, YAl(BO3)3 offering laser, self-frequency doubling and nonlinear optical properties. As active laser materials fluorides are discussed e.g. doped LiCaAlF6, LiSrAlF6 crystals. Important group of materials applied in laser technique are materials showing nonlinear absorption, which are used for passive modulation (Q-switch). YAG crystals doped with Cr, V, Co are presented.
We report the optical and lasing characteristics of neodymium doped lanthanum scandium borate. Nd:LSB microchip laser devices were fabricated from the conventional Czochralski pulling method with different doping concentration. The space group of Nd:LSB was studied with their optical characteristics. In the lasing experiment the hot-band pumping, 4F3/2, showed an improvement of slope efficiency and threshold comparing to the conventional pumping to 4F5/2 absorption band.
For accurate design and modeling of nonlinear optic polymer electro-optic (EO) waveguide devices, potential materials need to be thoroughly characterized. Presented here are the properties of several state of the art materials used for nonlinear optical (NLO) polymer devices, such as Cheng Larry Dalton (CLD) based NLO polymers as well as conductive polymers and epoxies. This characterization includes refractive index, propagation loss, conductivity, nonlinearity, and low and high frequency dielectric constant measurements, as well as materials compatibility.
An iterative method is applied to the analysis of N-coupled ring resonators. Splitting of the modes into N higher-Q modes occurs when the round-trip phase shifts in each ring are equal, in agreement with results for planar resonators and whispering gallery modes (WGMs) in coupled microparticles. This mode-splitting is, therefore, a universal phenomenon for resonant structures, and can lead to reduced thresholds for nonlinear optical effects.