Qingtian Gu

Optical properties of NAEC-PMMA nonlinear polymeric thin film

Novel guest nonlinear optical (NLO) chromophore molecules (4′-nitrobenzene)-3-azo-9-ethylcarbazole (NAEC) were doped in poly (methyl methacrylate) (PMMA) host with a concentration of approximately 15% by weight. For a useful macroscopic electro-optic (EO) effect, these NLO molecules NAEC were arranged in a noncentrosymmetric structure in the host polymer by corona-onset poling at elevated temperature (COPET). For applying NAEC-PMMA polymer in optical devices such as EO switch, its optical properties have been investigated. The UV/Visible absorption spectra for the unpoled and poled polymer film were determined. The refractive index of the film was also determined from measurements of the coupling angles with the reflective intensity at 632.8 nm wavelength. Using the simple reflection technique, the EO coefficient γ33 value was measured as 60 pm/V at 632.8 nm wavelength. The second-order nonlinear coefficient d33 was characterized by the second-harmonic-generation (SHG) experimental setup and the calculated d33 value reached 18.4 pm/V at 1064 nm wavelength. The relation between the second-order nonlinear coefficients d33 and d13 for the poled polymer film was also discussed in detail and the ratio d33/d13 value was obtained as 3.3.

Synthesis and characterization of thiazolylazo chromophore for nonlinear optical applications

Bathochromic thiazolylazo second-order nonlinear optical chromophore, having 2-hydroxylethyl group in a molecule, has been prepared. The temperature decomposition of the chromophore was measured by differential scanning calorimetry (DSC). The second-order polarizabilities at zero energy and the dispersion of second-order polarizabilities were measured by solvatochromic method. The other parameters of the chromophore were also measured.

Thermal stability and transmission losses of the poled polyimide side-chain thin films

Abstract The new side-chain polyimide thin films have been prepared. Through in situ second-harmonic generation (SHG) measurement, the corona poling temperature has been optimized by measuring the temperature dependence of in situ SHG signal intensity under the poling electric field. The second-order NLO coefficient χ 33 (2) =5.6 pm/V at λ =1064 nm was determined by using Maker fringe method after poling the films at optimal poling condition. The depoling knee temperature of the poled polyimide films can reach up to 200°C. Their lower-order optical waveguide-propagation losses were measured at 632.8 nm. The measurements have shown that the optical loss of the fundamental mode is less than 1.0 dB cm −1 for TE polarization.

Synthesis and characterization of nonlinear optical chromophores containing α-cyan with thermal stability

Abstract Nonlinear optical donor–acceptor chromophores containing α-cyan were synthesized. The decomposition temperature was determined by differential scanning calorimetry, and the absorption spectra were measured. The molecular first hyperpolarizabilities were measured by solvatochromic method, and the dispersion of linear electro-optic effects was firstly measured according to the experimental results of UV spectrum and dielectric constants for three chromophore molecules. And an additional merit of these chromophores has a noticeably high thermal stability and good solvability.

Thermally stable chromophores for nonlinear optical applications

Three thermal organic second-order nonlinear optical chromophores were synthesized. The decomposition temperature was determined by DSC, and the absorption spectra was measured. The second-order polarizabilities at zero energy and the dispersion of second-order polarizabilities were measured by solvatochromic method.

Electro-optical Properties and Temporal Stability of the Guest-Host DCNP/PEK-c Polymer Thin Film

The polyetherketone (PEK-c) guest-host system thin films in which the range of the weight percent of 3-(1,1-dicyanothenyl)-1-phenyl-4, 5- dihydro-1H-pryazole (DCNP) is from 20% to 50% were prepared. The predicted high value of electro-optical (EO) coefficient gamma(33) = 48.8 pm/V by using two-level model was obtained when the weight percent of DCNP in the polymer system is 40%, whereas EO coefficients are attenuated at higher chromophore loading then 40%. The temporal stability of the EO activity of the guest-host polymer was evaluated by probing the decay of the orientational order of the chromophores in the polymer system.

Formation of scatter particles in KDP (DKDP) crystals

Abstract Scatter particles in potassium dihydrogen phosphate crystal and deuterated potassium dihydrogen phosphate crystals have been observed and described by using transmission electron microscopy. The components were analyzed by electron probe microanalyzer. The formation mechanism of the scatter particles is proposed and discussed.

Investigation on (100) face of KDP crystal poisoned by MoO42− impurity

Potassium dihydrogen phosphate (KDP) single crystals doped with molybdate (MoO42−) were grown via the conventional temperature cooling and rapid growth methods, respectively. MoO42− made KDP crystals tapering for conventional temperature cooling method. When KDP crystals were grown by rapid growth method, MoO42− could induce liquid inclusions and simultaneous crystals. The measurement on growth rates indicated that MoO42− broadened the dead zone and decreased the growth rate of (100) face of KDP crystals. The growth kinetic analysis in terms of two-dimensional nucleus and screw dislocation models implied that the energetic parameter γ/kT decreased with an increase of MoO42− concentration. The influence of MoO42− growth steps on (100) face of KDP crystal was observed through ex situ AFM technique. It gave evidence that MoO42− could postpone the step bunching and make the step edge curving and knaggy to reduce the edge free energy, which was in agreement with the growth kinetics calculations. Additionally, the poisoned mechanism of MoO42− and Fe3+ on step morphologies was detailed contrasted. The interaction process was discussed according to electro negativity analysis, which indicated MoO42− (actually were HMoO4− and H2MoO4) could be absorbed onto (100) face through charge-assisted hydrogen bonds and caused more Mo element distributed in prismatic sector.

Side radical influence on the nonlinear optical properties and thermal stability of poled polymer films

Films of polyetherketone doped with the chromophores Disperse Red 1 (DR1) and Disperse Red 13 (DR13) were prepared by spin-coating method. By the in situ Second-harmonic Generation (SHG) signal intensity measurement, the optimal poling temperatures were obtained. For the investigated polyetherketone polymer doped with DR1 (DR1/PEK-c) and polyetherketone polymer doped with DR13 (DR13/PEK-c) films, the optimal poling temperatures were 150°C and 140°C, respectively. Under the optimal poling conditions, the high second-order nonlinear optical coefficient χ33(2) = 11.02 pm/V has been obtained for the DR1/PEK-c; and for DR13/PEK-c at the same conditions the coefficient is 17.9 pm/V. The SHG signal intensity DR1/PEK-c could maintain more than 80% of its initial value when the temperature was under 100°C, and the SHG signal intensity of the DR13/PEK-c could maintain more than 80% of its initial value when the temperature was under 135°C.

Effect of cyclohexane diamine tetraacetic acid on micro morphology of rapidly grown potassium dihydrogen phosphate crystals

Potassium dihydrogen phosphate (KDP) crystals were grown from aqueous solutions with different concentrations of cyclohexane diamine tetraacetic acid (CDTA) by the “point seed” rapid growth technique. The effects of CDTA on the surface micro morphology of KDP crystals were systematically studied by atomic force microscopy. The prismatic face growth rates of KDP crystals grown from various solutions were measured by a laser polarization interference system. The results shown that the steps became smooth after CDTA doping. When the doping concentration of CDTA is 100 ppm, the bunching of steps on the (100) face reduced dramatically and the step velocity increased obviously due to the complexation between CDTA and the metal impurities in the original solution. When the doping concentration of CDTA is 500 ppm, the excess CDTA adsorbed on the growth surface and impeded the step movement, leading to an increase in step bunching and reduction in step velocity compared with the situation of 100 ppm.