G.H Zhang

Investigation of Bimetallic Thiocyanates belonging to ABTC Structure Type: ZnCd(SCN)4 and AHg(SCN)4 (A = Zn, Cd, Mn ) as Nonlinear Optical Crystal Materials

Bimetallic thiocyanate complexes crystal materials belonging to ABTC structure type: ZnCd(SCN) 4 and AHg(SCN) 4 (A = Zn, Cd, Mn) which are potentially useful in second harmonic generation (SHG) have been prepared. Their structural, optical and physicochemical properties are characterized by infrared spectroscopy, X-ray powder diffraction, vis/UV/NIR spectroscopy, SHG measurements and thermal analysis. The states of crystal growth solutions are discussed in this article. The crystals belong to tetragonal system with the space group I4 and exhibit SHG efficiencies over one order of magnitude higher than that of urea. Their transparency cutoffs lie in the UV region, and they possess good physicochemical stabilities.

CW dual-wavelength Nd:YAG laser at 946 and 938.5 nm and intracavity nonlinear frequency conversion with a CMTC crystal

Abstract We report on the efficient CW dual-wavelength operation of a Nd:YAG laser at 946 and 938.5 nm. A total output power of 527 mW was obtained with a slope efficiency of 34%. By inserting a cadmium mercury thiocyanate (CMTC) crystal into the Nd:YAG laser cavity, frequency-doubling of 946 nm and sum-frequency-generation of 946 with 938.5 nm were realised simultaneously. Blue light at 473 and 471.1 nm with an output power of 1.6 mW was obtained. Phase matching calculations were also done for the CMTC crystal.

Growth, spectroscopic and thermal behavior of Cd(SCN)2(DMSO)2

Abstract Single crystals of the organometallic material, bis(dimethyl sulfoxide) cadmium thiocyanate (DSTC), Cd(SCN) 2 (DMSO) 2 were grown from aqueous solution. The grown crystals were characterized by elemental analyses, X-ray powder diffraction, Raman, infrared and optical transmission spectroscopy and thermal analysis. The UV transparency cutoff of DSTC crystal is 263xa0nm. It exhibits good physicochemical stability up to 134°C, and the final residue of thermal decomposition is CdS.

Intracavity-frequency-doubling of a 946 nm Nd:YAG laser with cadmium mercury thiocyanate crystal

We report the intracavity-frequency-doubling of a 946 nm Nd:YAG laser with a CMTC crystal at room temperature. A cw output power of 1.64 mW of blue light at 473 nm is obtained. To our knowledge, this is the first time that CMTC crystal has been used to frequency double a 946 nm Nd:YAG laser.

Investigation on growth and macro-defects of a UV nonlinear optical crystal: ZnCd(SCN)4

Abstract Large single crystals of the coordination complex nonlinear optical material zinc cadmium thiocyanate, ZnCd(SCN) 4 (abbreviated as ZCTC), were grown from aqueous solutions by the solvent evaporation method. The morphology of the crystals was indexed. The grown crystals were characterized by the powder X-ray diffraction analysis allowing to identify the diffraction planes. Six kinds of macro-defects were found in ZCTC large crystals. These defects include cracks, inclusions, negative crystals, growth striations, sector boundaries and straight pipes. The morphologies and distribution regularities of these defects were observed and analyzed using optical microscopy. Their formation mechanisms and the methods of eliminating these defects are discussed.

A CONTINUOUS-WAVE TUNABLE SOLID-STATE BLUE LASER BASED ON INTRACAVITY SUM-FREQUENCY MIXING AND PUMP-WAVELENGTH TUNING

We report on continuous-wave tunable blue-light generation from a Nd:Y3Al15O12 laser by intracavity sum-frequency mixing of its fundamental laser line at 946 nm with the pump light from a tunable Ti:sapphire laser by use of cadmium–mercury–thiocyanate nonlinear crystal. The tunable range of the blue light was 434.4–437.5 nm, and the maximum output power at 436 nm was measured to be 310 μW.

Ex situ atomic force microscopy studies of growth mechanisms of cadmium mercury thiocyanate crystals

Abstract Ex situ atomic force microscopy (AFM) has been used to investigate the growth mechanisms of the cadmium mercury thiocyanate, CdHg(SCN)4 (CMTC), crystal. Simultaneous spiral dislocation controlled growth and two-dimensional (2D) nucleation growth have been observed on {1xa01xa00} faces of the CMTC crystal grown at 30°C at supersaturations σ=0.24 and 0.01. Circular or irregular 2D nuclei have been observed at the large step terraces generated by the spiral dislocation sources. The combination of spiral controlled growth and 2D nucleation growth expedites the growth rate of the large steps leading to the pile-up of elementary steps. When the CMTC crystal is grown at 30°C and supersaturation σ=0.01, a multiple growth mechanism is found. Two-dimensional nuclei have been observed to coexist with dislocation spiral hillocks as well as multilayer stacks. The appearance of 2D nuclei as well as several 3D nuclei is assumed to result from the direct association of some solute aggregations in the growth solution. It is notable that the surface morphology of the multilayer stacks is greatly changed by multiple scanning. This is attributed to restructuring of the crystal surface due to an internal energy increase caused by multiple scanning.

Refractive index and absorption of lead bromide crystals

Abstract Lead bromide (PbBr2) crystals in [001] orientation were obtained by the Bridgman growth method. The orientation of the principal refractive axes of the crystals was determined, and their principal refractive indices were measured by the least deviation angle at eight selected wavelengths. The optical axial angle and the dispersion of refractive index in the visible spectral range were calculated by Sellmeier’s formula. Optical transmission and reflection spectra were measured and the absorption coefficient α was determined. Using the calculated α(hν) dependence, the bandgap width corresponding to indirect transition was determined.

Growth morphology of {100} faces of zinc cadmium thiocyanate crystal investigated by atomic force microscopy

Abstract Morphology of the (1xa00xa00) face of zinc cadmium thiocyanate crystal before and after its growth at 30(±0.05)°C at a supersaturation of 0.087 has been studied. Highlands formed by chains of small growth hillocks generated by spiral dislocation sources and small cavities adjacent to the hillocks have been observed. The small cavities are assumed to result from continuous growth of large hollow channels at the top of the highlands rather than being hollow cores indicative of spiral dislocation growth. Strings of similar cavities are also found at “macrosteps”. All highlands and strings of cavities are oriented along the [0xa01xa00] direction, which manifests a strong anisotropic growth at this face associated with the strong PBC bonds along this direction.

Atomic Force Microscopy Studies on Growth Mechanisms and Defect Formations on {110} Faces of Cadmium Mercury Thiocyanate Crystals

Growth mechanisms and defect formations on {110} faces of cadmium mercury thiocyanate crystals grown at 30°C (σ = 0.24)were investigated by using atomic force microscopy (AFM). It was found that, under this condition, spiral dislocation controlled mechanism and 2D nucleation mechanism operates simultaneously and equally during growth, which is completely different from the traditional 2D nucleation and dislocation source controlled mechanisms. A number of 2D nucleus are formed at the large step terraces generated by dislocation sources, leading to the unequal growth rates of the elementary steps and thereby step bunches are caused. Various defects are formed under this growth condition, which is assumed to result from the incongruence between the steps generated by different sources. A new kind of 2D defect, corresponding to one growth layer in height, was observed for the first time.