G.H. Zhang

Physicochemical behavior of nonlinear optical crystal CdHg(SCN)4

Abstract The preparation and purification of cadmium mercury thiocyanate, CdHg(SCN)4 (CMTC) are described. The identity of the synthesized compound was characterized by Raman, infrared and X-ray powder diffraction spectra. The thermal stability and thermal decomposition of CMTC crystals were investigated by means of thermogravimetric analysis and differential scanning calorimetry. The impurities in the growth solutions and their effects are discussed.

Diode-pumped passively Q-switched mode-locked Nd:LuVO4 laser with a semiconductor saturable absorber mirror

We present a compact passively Q-switched mode-locked Nd:LuVO4 laser run in a Z-type folded cavity with semiconductor saturable absorber mirror (SESAM). The repetition rates of the passively Q-switched pulse envelope ranges from 22.99 to 141.18 kHz as the pump power increased from 2.372 to 8.960 W. The repetition rates of mode-locked laser pulses in the Q-switched pulse envelope has 111 MHz determined by the cavity length and the mode-locked pulse duration is evaluated to be 257 ps. An average output power of 823.5 mW is achieved at the pump power of 8.96 W, corresponding to an optical conversion efficiency of 9.2%.

A systematic spectroscopic study of four bimetallic thiocyanates of chemical formula AB(SCN)4: ZnCd(SCN)4 and AHg(SCN)4 (A=Zn, Cd, Mn) as UV nonlinear optical crystal materials

Abstract Bimetallic thiocyanate complexes of chemical formula AB(SCN)4(ABTC): ZnCd(SCN)4 and MHg(SCN)4 (M=Zn, Cd, Mn) were discovered as potentially useful crystal materials in ultraviolet second-harmonic generation. The structures of these compounds were derived from powder X-ray diffraction data, and unit-cell parameters were calculated by the TREOR program. Their vibrational spectra were studied by Raman spectroscopy, which show that the characteristic vibrational modes of AB(SCN)4 crystals arise mainly from the internal vibrations of the SCN, A(NCS)4, and B(SCN)4 clusters. The reason of the high optical nonlinearities of ABTC crystals has been studied by the use of the Raman spectra and the molecular orbital theory: the distorted A(NCS)4 and B(SCN)4 tetrahedra and the conjugated charge-transfer (–A–NCS–B–) bridges that connect all the distorted tetrahedra together.

Theoretical calculation and vibrational spectral analysis of L-arginine trifluoroacetate.

Fourier transform infrared and Raman spectra of the nonlinear optical crystal, L-arginine trifluoroacetate (L-arginine.CF3COOH, abbreviated as LATF) have been calculated by the first-principles calculation and investigated in experiment. The calculated results are slightly different from those experimental values because of the distinction resulted from the intermolecular hydrogen bonds. The role of this type of intermolecular interaction on the crystal vibrational spectra and nonlinear optical properties has been discussed. The absorption-edge on the IR side has been estimated by the theoretical approach on basis of the calculated infrared spectrum, which will be meaningful for further research on NLO crystal.

Vibrational spectra and theoretical study of ZnCd(SCN)4 single crystal

Abstract The vibrational spectra of the zinc cadmium thiocyanate (ZCTC) single crystal are studied by Raman spectroscopy and ab initio calculation with the molecular orbital (MO) theory using a G aussian 98 program. Agreement is achieved between the vibrational wavenumbers predicted by the theory and those observed in Raman scattering experiments. The results show that the characteristic vibrational modes of ZCTC crystal arise mainly from the internal vibrations of the SCN, Zn(NCS)4, and Cd(SCN)4 clusters. The three-dimensional network structure of ZCTC crystal is identified, and the high optical nonlinearity of the crystal is chiefly ascribed to the conjugated charge-transfer (–Zn–NCS–Cd–) bridges that connect all the distorted Zn(NCS)4 and Cd(SCN)4 tetrahedra together.

Investigation of the Solution Structures and Determination of the Growth Units of Cadmium Mercury Thiocyanate Crystal

To get a better understanding of the growth of cadmium mercury thiocyanate (CMTC), a promising nonlinear optical crystal, we have investigated the structures of its growth solutions by using Raman spectra. It has been found that Hg(II) ions coordinate with SCN - through S atoms, forming the most stable complex of [Hg(SCN) 4 ] 2- in the solutions while Cd(II) ions bind to SCN around Hg(II) through the other end N atom. Thereby, taking [Hg(SCN) 4 ] 2- anions as centers, a network structure of Cd(II)-N-C-S-Hg(II) is formed in the solutions as in the crystal lattice. It is notably that there are other complexes, mostly the Cd(SCN) n (n<4) complexes, in the solutions. Therefore, the solution structure of CMTC is complicated, which is believed to contribute greatly to the difficulty of growing large single crystals. Based on the analysis of the solution structures, the reasonable growth units of CMTC are proposed.

Surface morphology of {100} faces of L-arginine phosphate monohydrate single crystals investigated by atomic force microscopy

Surface morphology of (100) faces of LAP crystals was investigated by atomic force microscopy (AFM). Both the steps and the two-dimensional nuclei elongate along the b direction, which is determined by the crystal structure. Fluctuations in the growth conditions could result in the formation of protuberances on the step fronts. Tree-like growth belts are initially observed on LAP crystals. It is assumed that the formation is caused by uneven liquid flow of the mother solution.

EX SITU ATOMIC FORCE MICROSCOPY STUDIES OF GROWTH MECHANISMS OF MANGANESE MERCURY THIOCYANATE CRYSTALS

Growth mechanisms of the {110} planes of the manganese mercury thiocyanate, MnHg(SCN)4 (MMTC), crystals have been investigated by using atomic force microscopy (AFM). The results show that spiral dislocation controlled mechanism and two-dimensional (2D) nucleation mechanism operate simultaneously during growth. 2D nuclei are found to cover up the outcrop of dislocation hillocks. Pairs of circular 2D nuclei appear on the wider steps terraces and the slope of 2D nucleation islands. Hillocks introduced by both simple spiral dislocation sources and 2D nucleation are elliptical in shape. It is determined the long sides orientate along the c-direction or the direction about 45° to the c-axis. Anisotropic growth hillocks and isotropic 2D nuclei coexist on the surface, which may be due to unequal supersaturations in the mother solution during the evaporation process.

ATOMIC FORCE MICROSCOPY STUDIES ON GROWTH STEPS AND 2D NUCLEI ON THE {100} FACES OF DEUTERATED L-ARGININE PHOSPHATE CRYSTALS

Growth steps and 2D nuclei of the {100} faces of the deuterated L-arginine phosphate (DLAP) crystals have been studied using ex-situ atomic force microscopy (AFM). Straight steps along the b direction as well as meandered steps are detected. The bunched steps have wider terraces than the elementary ones, which are supposed to result from the slower growth rate of the former than the latter. Many 2D nuclei exist on the step terraces and edges acting as the growth sources. Occasionally, 2D islands generated by 2D nuclei could also be observed. In conclusion, the crystal grows by layer growth mechanism.

Third-order optical nonlinearity of a novel material : [ (C4H9)4N] [Co (dmit )2]

A novel dmit organometallic complex—[(C4H9)4N][Co(dmit)2] (dmit2− = 4,5-dithiolate-1,3-dithiole-2-thione), abbreviated as BuCo, is synthesized and its third-order optical nonlinearity of the acetone solution is characterized using the Z-scan technique with a 40-ps pulse width at 1064 nm. Z-scan curves show that BuCo sample solution possesses the negative nonlinear refraction, exhibiting a self-defocusing effect. In addition, the two-photon absorption has been observed in BuCo. The effective molecular second-order hyperpolarizability γeff of the BuCo molecule was estimated to be as large as 5.60 × 10−31 esu, suggesting BuCo is a potential material for optical device applications.