Dispersion of the linear and nonlinear optical susceptibilities of disilver germanium sulfide from DFT calculations

The dispersion of the linear and nonlinear optical susceptibilities is calculated for disilver germanium sulfide (Ag₂GeS₃) using the all-electron full potential linearized augmented plane wave (FP-LAPW) method. Calculations are performed with four exchange correlations namely local density approximation (LDA), general gradient approximation (GGA), Engel–Vosko generalized gradient approximation (EVGGA), and modified Becke–Johnson potential (mBJ). Our calculations give a band gap of 0.40 eV (LDA), 0.42 eV (GGA), 1.03 eV (EVGGA), and 1.30 eV (mBJ) in comparison with our measured gap (1.98 eV). The mBJ exchange correlation gives the best agreement with experiment. We find that the calculated linear optical susceptibilities of Ag₂GeS₃ show considerable anisotropy which is useful for second harmonic generation and optical parametric oscillation. To analyze the spectra of the calculated χ ₁₁₃ ⁽²⁾ (ω), χ ₂₃₂ ⁽²⁾ (ω), χ ₃₁₁ ⁽²⁾ (ω), χ ₃₂₂ ⁽²⁾ (ω), and χ ₃₃₃ ⁽²⁾ (ω), we have correlated the features of these spectra with the features of ?₂(ω) spectra as a function of ω/2 and ω. From the calculated dominant component |χ ₃₃₃ ⁽²⁾ (ω)|, we find that the microscopic second-order hyperpolarizability, β₃₃₃, the vector components along the dipole moment direction is 41.2 × 10^?30 esu at static limit and 222.9 × 10^?30 esu at λ = 1064 nm.     

Dispersion of the nonlinear refractive index of optical crystals

The nonlinear refractive indices of several important optical materials have been measured at the second and third harmonic wavelengths of the Nd laser using nearly degenerate four-wave mixing. Measurements made relative to the nonlinear index of fused silica have the highest accuracy. Absolute measurements were also made using the Raman cross-section of benzene as a nonlinear reference standard. The relative measurements are compared with a despersion model base on parameters fitted to the linear refractive indicies and also to a recently proposed model based on Kramers-Kronig transformation of the calculated, two-band, two-photon loss spectrum.     

Retrieval of linear optical functions from finite range spectra

There are many experimental situations in which infrared reflectivity spectra can be acquired only over a limited spectral range. It is therefore necessary to find computing procedures that allow the efficient analysis of such data. In this paper, we propose a new procedure labeled constrained finite range correction (CFRC) that can be advantageously substituted to multiply subtractive Kramers-Kronig relations. The constrained finite range correction is able to produce realistic results even when very little supplementary information is available. For semitransparent crystals, the hypothesis of the phase spectrum positiveness alone is often sufficient to compute satisfactory approximations of the optical functions. The efficiency of the new method is shown through the analysis of several synthetic and experimental spectra.     

非线性光学晶体三硼酸铋的拉曼光散射

结构分析表明非线性光学晶体三硼酸铋BiB3 O6的晶胞参数为a1=0 .7116nm ,a2 =0 .4993nm ,a3 =0 .65 0 8nm ,β =10 5 .62° ,每个初基晶胞含有二个分子。在不同几何配置下的激光拉曼光谱观察到了晶体中硼氧四面体和硼氧三角形的特征晶格振动和振动模的分裂。拉曼光谱表明晶体的内部结构有很强的各向异性 ,这就是晶体非线性光学性质的来源     

Molecular design and synthesis of branched bichromophore-attached linear fluorinated polyimides for nonlinear optical applications

A branched structure bichromophore was developed to increase the nonlinearity of optical polymers. The branched bichromophore was incorporated into the polymer backbone to prepare a novel nonlinear optical (NLO) side-chain fluorinated polyimide with high optical nonlinearity and good thermal stability. The novel nonlinear optical side-chain fluorinated polyimide exhibits a large electro-optic (E-O) coefficient (γ₃₃) (34 pm/V at 1550 nm) which is larger than that of the conventional side-chain optical polyimide. This is mainly attributable to an increased chromophore concentration and high polarizing efficiency derived from the branched structure. The branched structure of the bichromophore is incorporated into a polymer backbone to result in a high chromophore concentration. Moreover, the three-dimensional (3D) architecture and large molecular size of the branched bichromophore can spatially shield from strong interchromophore electrostatic interactions to enhance the poling efficiency. The side-chain fluorinated polyimide exhibits excellent solubility in common organic solvents, good film-forming property, high glass-transition temperature (T _g) (190 °C) and thermal stability up to 235 °C.     

Smart NIR linear and nonlinear optical nanomaterials for cancer theranostics: Prospects in photomedicine

Light-based diagnostics and therapy have become indispensable tools in the field of cancer nanomedicine. Various optical imaging modalities with tomographic capability have been developed to visualize cellular and organismic distributions of molecules. Microscopic pharmacokinetics and the tumor-targeting efficacy of nanoscale effectors can now be precisely evaluated. Moreover, phototherapy using intense laser light has been widely used for treating cancers. Using light-active nanoscale effectors, photothermal and photodynamic therapies on superficial tumors can be achieved with low-illumination lasers. Consequently, for the next generation of photo-medical techniques, the use of near infrared (NIR) excitation sources on NIR-activatable nanoparticles may offer deeper light penetration owing to less extensive scattering and absorption by endogenous chromophores in the NIR spectral region. Therefore, treatments and biodetection within higher tissue volumes and with less side effects (e.g. overheating) may be successfully implemented. This comprehensive review covers the state-of-the-art technologies on (a) advanced laser light sources appropriate for deep tissue theranostics, (b) types of laser interactions with pure-NIR and NIR-upconverting nanomaterials, (c) current development of NIR and multi-photon nanoparticles, (d) application fields of NIR nanomaterials in cancer theranostics, and (e) nanotoxicology of NIR nanoscale effectors for cancer treatment.     

实验室能力评审的有效性探讨

本文从实验室能力评审的内涵、评审过程存在问题和评审实例出发,对目前实验室认可与资质认定(计量认证)能力评审活动的有效性进行了探讨。     

Universal relations for nonlinear electroelastic solids

Summary Electro-sensitive elastomers are materials that can support large elastic deformations under the influence of an electric field. There has been growing interest recently in their applications as so-called ``smart materials'. This paper is devoted to the derivation of universal relations in the context of the nonlinear theory of electroelasticity that underpins such applications. Universal relations are equations relating the components of the stress, the electric variables and the deformation that are independent of the constitutive law for a family of materials. For the general constitutive equations of an isotropic electroelastic material derived from a free energy function and for some special cases of these equations, we obtain universal relations, the word ``universal' being relative to the considered class or subclass of constitutive laws. These universal relations are then applied to some controllable states (homogeneous and non-homogeneous) in order to highlight some examples that may be useful from the point of view of experimental characterization of the material properties. Additionally, we examine the (non-controllable) problem of helical shear of a circular cylindrical tube in the presence of a radial electric field, and we find that a nonlinear universal relation that has been obtained previously for an elastic material also holds when the electric field is applied.     

Dispersion study on third-order nonlinear optical properties of organic species with nitronyl nitroxide radical

The third-order nonlinearity of five stable organic radical species with nitronyl nitroxide group was investigated using a femtosecond optical Kerr gate method. The magnitudes of their second hyperpolarizability were measured at around 10^{- 34} -10^-32 esu. The influence of the subtle chemical change of the molecular structure was explored. The experimental results were compared with theoretical calculation.     

Dispersion relations and normal modes for magnetoelastic waves in ferromagnetic insulators

The dispersion relation and the normal modes for magnetoelastic waves in ferromagnetic insulator crystals are calculated when the interaction between magnetization and strains is approximated to a bilinear form of creation and annihilation boson operators. Numerical results are obtained for YIG.     

Isotropic linear constitutive relations for nonsimple fluids

We investigate the general constitutive relation of an isotropic linear fluid when the stress tensor can depend on higher-order spatial gradients of the velocity. We apply the results to the case of second-grade and third-grade fluids, be they compressible or not. However, the expression of the general isotropic tensor can be a matter of interest also for other classes of nonsimple material.     

Dispersion relations of the high-frequency modes in3He-B

The dispersion relations for the high-frequency modes in³He-B are obtained for finite temperature and including Fermi liquid corrections. The coupling between zero sound and the squashing mode is studied in detail. It is shown to have a more complicated structure than what was previously believed. Finally, it is shown that there are no modes with frequency around 2.     

Cyclic interferometers for optical testing

In this paper, we describe two compact cyclic interferometers which can be used for the testing of right-angle prisms; with some modifications they can also be used for testing convergent wave fronts.     

Structural,linear and third-order nonlinear optical properties of Cu nanocrystal in sodium borosilicate glass

Cu nanocrystals embedded in sodium borosilicate glass of varied Cu contents from 0.5 to 1.5 wt% have been successfully prepared through a sol–gel process. According to the results of X-ray diffraction (XRD) and the energy dispersive X-ray spectrometry (EDS), the metal Cu nanocrystals in cubic crystal system were well distributed inside glass matrix. Fourier Transform Infrared (FTIR) indicated the sodium borosilicate matrix had no major structural change for gels with different Cu contents. The optical absorption peaks due to the surface plasmon resonance of Cu particles were observed in the wavelength range of 550–600 nm. The absorption peak showed a red-shift trend with increasing Cu contents from 0.5 to 1.5 wt%. Transmission electron microscopy (TEM) revealed the existence of spherical Cu nanocrystals in the matrix. The diameter of Cu nanocrystals varied from 1 to 3.5 nm. Furthermore, the third-order nonlinear optical properties were investigated by Z-scan technique at 800 nm. Experimental results indicated the Cu nanocrystals have obvious positive refractive nonlinearities and reverse saturated absorption performance.     

Langmuir-Blodgett films for nonlinear optical applications

Azo-benzene chromophores with an oxygen donor and five different end-groups have been attached to octadecyl chains or to polysiloxane backbones via hexadecyl spacer groups. These were deposited by the Langmuir-Blodgett (LB) technique using our own design of diamond-barrier trough. The LB deposition properties of the polymers were superior to those of the low molecular mass materials, which did not show second harmonic generation (SHG) as deposited monolayers. The strength of SHG from the polymers correlated with acceptor strength, but the maximum signal was only about 10% of that of hemicyanine. Only one of the polymers gave thick films of very high quality; this had a hydroxyl end-group and showed no SHG except when deposited from an acid subphase. This was presumed to result from protonation of the azo group to create an acceptor. The quality of the deposited films may correlate with their phase behaviour; the best material showed only a presumed soft crystalline phase. The film-forming properties of that film were remarkable; loss figures of around 2.5 dB cm^–1 have been recorded at 633 nm in films of 1.3 m thickness. Future work will seek to isolate and independently control the factors involved in good film formation and in high SHG.