Wen Shan Wang

Crystal growth and optical properties of 4-aminobenzophenone crystals for NLO applications

Single crystals of 4-aminobenzophenone, a nonlinear optical (NLO) material have been grown successfully by a novel solution growth as well as modified Bridgman-Stockbarger techniques. The transmission spectrum (420-1400 nm) and SHG efficiencies were determined. 4-Aminobenzophenone crystals gave a lower limit on the second harmonic generation (SHG) efficiency of 10%. Laser damage threshold measurements conducted at the indicated wavelengths gave values of 1-2 GW/cm 2 .

Morphology and formation of the color core of Bi12SiO20 crystals grown by the Czochralski method

Single crystals of pure and Fe 3+ doped bismuth silicon oxide (Bi 12 SiO 20 ) have been grown by the Czochralski method. Bi 12 SiO 20 crystals grown over a wide range of conditions show an obvious tendency towards faceting. The faceting morphologies of crystals grown along (001) and (111) are reported. During growth, Bi 12 SiO 20 (BSO) crystals abruptly withdrawn from the melt confirmed the presence of interfacial (110) facets and revealed a conical interface surface in the regions between the facets. In addition, the color core in single crystals of Bi 12 SiO 20 grown by the Czochralski method has been analyzed using quantitative energy dispersive X-ray spectroscopy

A novel Bridgman-Stockbarger melt growth system for organic nonlinear optical materials

A modified Bridgman-Stockbarger crystal growth system has been designed and fabricated by relatively low-temperature (up to 250 degrees C) nonlinear optical organic materials. The novel feature is that the crystal melt surface can be viewed from any direction and the temperature gradient between the hot and cold zone can be adjusted at any time. The ampoule can be lowered at a rate as slow as 0.1 mm h-1. The temperature can be maintained to a precision of +or-0.01 degrees C. High-quality single crystals of benzil have been successfully grown using this system.

Photonic crystals: Crystal growth processing and physical properties

Publisher Summary This chapter discusses crystal-growth fundamentals and the dependence of the crystal-growth process on the physical and chemical state of the solid–liquid interface. Convection is a key transport mechanism that affects the shape of the crystal–melt interface, the concentration distribution, and macro–micro defects. However, this chapter focuses on only basic differential equations and the simplest concepts—such as a few important nondimensional numbers (Re, Gr, Pr, Sc, Ra, and Ma). Crystal growth by the Czochralski, modified Bridgman–Stockbarger, top-seeded solution, and low-temperature solution growth methods are summarized and adequate details are given for fabricating the systems designed and used in laboratory for the growth of high-quality crystals. To further assist in designing and fabricating good equipment for growing crystals by melt processes, information on heating methods, temperature control techniques, and the selection of suitable crucible materials is provided.

A versatile low‐cost Czochralski crystal growth system for nonlinear optical organic materials

A versatile low‐cost Czochralski system for pulling crystals from melt has been described. It is designed for low melting, transparent, and nonlinear optical materials. One of the most important novel feature of this crystal growth system is that the entire growth process including the solid–liquid interface can be viewed from any direction. Another is the use of an after‐heater to reduce excess heat loss from the surface of the melt.

A versatile Czochralski crystal growth system with automatic diameter control

A versatile Czochralski crystal pulling system with automatic diameter control for the growth of nonlinear optical oxide crystals is discussed. Pure and doped bulk single crystals of bismuth silicon oxide (Bi12SiO20) have been successfully grown using this system. The system consists of a regular Czochralski type pulling system with provision for continuous weighing of the growing crystal to provide feedback for power control.

Benzil: 2-methyl-4-nitroaniline binary single crystals for nonlinear optical applications

Benzil:MNA binary organic single crystals have been grown to overcome decomposition tendency and improve mechanical properties of 2-methyl-4-nitroaniline (MNA) which is known to be one of the best organic NLO material. Single crystals of binary system have grown using a transparent Bridgman- Stockbarger system which has fabricated to monitor the growth process. The growth conditions for the flat solid- liquid interface are optimized for the different dopant concentration of benzil. The melt in the self-sealing ampoule is maintained in liquid state without decomposition up to 2 weeks which allows us to grow 20 mm long single crystals. Hardness of 5wt% benzil:MNA is measured to be 13 Kg/mm2 which is 45% higher than benzil. The conversion efficiency of second-harmonic generation is found to be 1.5% with 4.5 mm interaction length. Since MNA is phase-matchable material, this efficiency could be comparable to commercial KDP. Surface quality of binary crystals has maintained its initial condition in air without absorption of water vapor which may be the main cause of surface degradation.

Photoinduced charge transfer in BSO:Cr3+ homegrown single crystal at room temperature during grating formation under Ar+ laser illumination in EPR experiment

With a view to understand the microscopic origin of photoinduced charge transfer in the cubic BSO crystal, we have studied the EPR spectrum of BSO:Fe3+ and the effect of laser illumination on the EPR signal during photorefractive grating formation at liquid nitrogen and room temperatures. The BSO:Cr crystal was grown at Alabama A&M University using Czochralski technique and the EPR spectrum was recorded at room temperature. Three EPR signals were observed. The EPR signals are due to the main dopant Cr3+ and the weak presence of Fe3+ which is inherent in BSO crystal. The effect of Ar+ laser illumination revealed new facts about the behavior of Cr3+ under laser illumination which is opposite to the behavior of Fe3+ in BSO:Fe3+ under laser illumination. Forming a grid on the face of the crystal increases the light-induced charge transfer Cr2+/Cr4+ is equivalent to Cr3+. The use of laser illumination helped to shed more understanding on the assignment of the EPR signals as well as the dynamic behavior of the charge transfer processes.

Melt growth of a new nonlinear optical organic crystal triethylphosphine sulfide using modified Bridgman-Stockbarger technique

Triethylphosphine sulfide, [C2H5]3 P(S) (abbreviated as TPS), seems to be a potential nonlinear optical organic material. Bulk single crystals of this material were grown using modified Bridgman-Stockbarger method. Commercially available triethylphosphine sulfide, procured from Johnson Matthey, was purified by physical vapor transport using low pressure sublimation (approximately 30 mTorr). The growth conditions are being optimized. The temperature gradient was chosen to be 6 - 8°C/cm, and the ampoule lowering rate was chosen to be 0.2 - 0.4 mm/hr and cooling rate after the crystal growth run was 5 - 10°C/day. Several TPS single crystals with size 10x10x15 mm3 have been grown. The second harmonic generation was measured qualitatively and has been found to be comparable to phase matched potassium dihydrogen phosphate.

Growth and morphology of the nonlinear optical crystal 3-methoxy-4-hydroxy-benzaldehyde (MHBA)

3-methoxy-4-hydroxy-benzaldehyde (MHBA) is one of the new organic materials that has become important for nonlinear optics in recent years because of its large second order nonlinear optical susceptibility and good blue transparency. Single crystals of MHBA were grown by a modified solution growth method. A study has been performed to select a suitable solvent for the growth of this material and to determine the effects of the solvent on the morphology of the crystals. These solvents were first studied to see their effects on the characteristic morphology of the material. From the results of morphology studies, methanol, ethanol, and MEK were selected as possible solvents for the growth. The solubility of MHBA was measured as a function of temperature in each solvent. From the solubility data, we discovered that a mixture of methanol to water (1:1) showed the most promise as a solvent for the growth of MHBA from solution. Crystals were grown using the three solvents in an effort to confirm the results of the solubility test. The properties of the material were studied using Differential Scanning Calorimetry, Vickers hardness, and optical absorption spectrum. The results of the above measurements are described in this paper.