Thermo-optic dispersion formula for AgGaS2

AgGaS(2) has been found to be 90 degrees phase matchable at 192 degrees C for sum-frequency mixing between the output of the KTP parametric oscillator at 3.2627 mum and its pump source at 1.0642 mum. The thermo-optic dispersion formula that can be used for good reproduction of the temperature-dependent phase-matching conditions thus far reported in the literature as well as our new data for second-harmonic generation of a CO(2) laser and its harmonics at 1.7652-5.2955 mum is presented.     

硫镓银晶体热分析动力学

本文对AgGaS_2晶体的结晶过程进行了热分析动力学研究,获得了"动力学三因子"。利用动态多重扫描速率法获得的三个不同升温速率下的晶体结晶动力学参数,采用微分法Kissinger模型计算出AgGaS_2晶体结晶活化能为515.78KJ/mol,指前因子lnA为51.06,积分法FWO计算出结晶活化能为509.80kJ/mol,并运用普适积分法逻辑推导出AgGaS_2晶体结晶的最概然反应机制方程为Aurami方程Ⅱ。这对于了解AgGaS_2晶体的结晶动力学特性,生长大尺寸、高质量的AgGaS_2晶体具有非常重要的意义。     

AgGaS2晶体红外光谱的研究

用傅里叶红外光谱仪测量了硫镓银晶体的红外透率,得到晶体的红外透射谱.应用群论的知识,对硫镓银晶体中离子的振动方式与红外活性之间的内在关系进行了讨论,并根据硫镓银晶体的红外光谱实验数据,计算了透过率和吸收系数.晶体的红外透过率(67%)与文献报道相近,与理论值还有一定差距,说明晶体内部还有第二相析出物形成的微观散射中心等缺陷存在.     

High-resolution tunable mid-infrared spectrometer based on difference-frequency generation in AgGaS2

We have built a high-resolution and high-signal-to-noise ratio spectrometer for line shape studies of greenhouse gases in the mid infrared. The infrared radiation is generated in a AgGaS2 nonlinear crystal by the well-known difference-frequency method. The choice of crystal is explained, and a brief literature review is presented. With two tunable dye lasers and a type I, 90 degrees phase-matching geometry, the infrared is continuously tunable from 7 to 9 microm when Rhodamine 6G and Sulforhodamine 640 dyes are used. The total infrared power exceeds 30 nW and is limited by both the damage threshold and thermal loading of the crystal. Phase-sensitive detection allows us to reach signal-to-noise ratios in excess of 3500:1 while maintaining an instrumental linewidth of 1.5 MHz. However, we show that the spectrometer may be used to measure the positions of spectral lines within +/-400 kHz.     

AgGaS2晶体生长过程中的过冷度研究

根据熔体生长系统中相变驱动力的基础理论,针对AgGaS2过冷度较大的特点,采用自发成核后升温熔料、下降安瓿后上提熔料以及加类籽晶等工艺研究了AgGaS2晶体生长过程中因过冷度大而难于生长较大尺寸单晶体的问题,生长出了外形完整、无裂纹的尺寸达φ15mm×20mm的较高质量AgGaS2单晶体.     

AgGaS2单晶生长温场研究

根据AgGaS2晶体的生长习性,分析了AgGaS2晶体生长对生长炉温场的要求,设计了三温区的生长炉,并对其温场进行了测试实验.在测试结果中选择较好的温场进行AgGaS2晶体生长,得到了外形较完整、品质较高的晶体.     

Noise figure measurements on nonlinear devices

A study of the effect of a cubic nonlinearity on the Y-factor method for measuring noise figure is performed. By hypothesis, the Y-factor technique does not take nonlinearities into account. It is shown that the presence of the nonlinearity largely influences the measured noise figure value. An alternative, single-tone noise figure measurement setup is proposed to correct the problem     

Difference Frequency Generation in AgGaS(2): Sellmeier and Temperature-Dispersion Equations

Two single-mode diode lasers and AgGaS(2) as a nonlinear medium are applied for difference frequency generation (DFG) in the mid-infrared spectral range between 4.9 and 6.5 mum. Phase matching is achieved by either temperature tuning or angle tuning of the crystal. Experimentally measured sets of input wavelengths lambda(s) and lambda(p), the resulting DFG wavelength lambda(i), and corresponding phase-matching temperatures or angles are compared with the calculated values derived by use of different Sellmeier equations and coefficients and temperature-dispersion equations dn/dT. Our results show that only specific combinations of previously published Sellmeier equations, coefficients, and temperature-dispersion equations are suitable for exact calculations of phase-matching parameters. These combinations reproduce our experimentally obtained phase-matching temperatures and angles with an accuracy of better than 5% and are therefore of fundamental interest for the design of a mid-infrared DFG spectrometer with AgGaS(2) as a nonlinear medium.     

Effect of annealing on the optical quality of AgGaS2 and AgGaSe2 single crystals

Single crystals of AgGaS₂ and AgGaSe₂ were grown by a modified Bridgman-Stockbarger technique. Pieces of sizes 10 mm × 6 mm × 4 mm and 11 mm × 6 mm × 5 mm of AgGaS₂ and AgGaSe₂ free from lamellar twins, were cut from the crystals for detailed investigations. The results of infrared transmittance and absorbance measurements indicate that the optical quality of the annealed crystals was much better than that of the as-grown crystals. Experiments on thermal etching were also carried out to study the microscopic defects in the crystals.     

All-optical logic devices with cascaded nonlinear couplers

The switching behaviors of cascaded nonlinear couplers were investigated. They have nearly ideal digital-switching characteristics, and their output power levels can be adjusted by means of varying the nonlinear coupling coefficient of the final coupler. The two-input excitation nonlinear cascaded couplers can perform not only switching operations but also a series of logic operations. The logic operations depend mainly on the coupling length of the two-input coupler and its initial inputs. The power corresponding to the rising and falling ridge of the logic operating waveforms can be shifted effectively by means of varying the switching power of the reshaper. Allowable ranges of three important parameters-coupling length of the two-input coupler L(1), bias optical power P(bia), and phase difference psi between the signal and bias beams for six fundamental logic operations-were calculated. Curves for design considerations and suggestions for the best choice of parameters for stable and reliable logic operations and, or, xor, nand, nor, and nxor are also presented individually.     

Effect of Ionizing Radiation Parameters on the Properties of AgGaS2 Single Crystals

Inorganic Materials - We report X-ray dosimetric characteristics of AgGaS2 single crystals grown by the Bridgman–Stockbarger method. The 298-K X-ray induced conductivity coefficient of the...     

Fields in electrical devices containing soft nonlinear magnetic materials

The Colorado method for the solution of the non-linear form of Laplace's, Poisson's, and the diffusion partial differential equations is explained. Various boundary conditions can be satisfied. The transformation of the partial differential equation into a large set of finite difference equations is given. The discretization is based on a grid system consisting of two sets of orthogonal grid lines. The resulting meshes are nonuniform. Successive line overrelaxation method is used for the solution of the nonlinear equations in two steps. For the improvement of convergence, two methods of acceleration of convergence are described.     

Widely Tunable Continuous-Wave Mid-Infrared Laser Source Based on Difference-Frequency Generation in AgGaS(2)

We demonstrate difference-frequency generation in the 6.8-12.5-mum range by mixing two high-power single-frequency laser diodes in a type II AgGaS(2) crystal. This compact all-solid-state scheme provides maximum output powers that exceed 1 muW and permits continuous adjustment-free scans larger than 2 cm(-1) across the entire tuning range.     

Generating nonlinear concentration gradients in microfluidic devices for cell studies

We describe a microfluidic device for generating nonlinear (exponential and sigmoidal) concentration gradients, coupled with a microwell array for cell storage and analysis. The device has two inputs for coflowing multiple aqueous solutions, a main coflow channel and an asymmetrical grid of fluidic channels that allows the two solutions to combine at intersection points without fully mixing. Due to this asymmetry and diffusion of the two species in the coflow channel, varying amounts of the two solutions enter each fluidic path. This induces exponential and sigmoidal concentration gradients at low and high flow rates, respectively, making the microfluidic device versatile. A key feature of this design is that it is space-saving, as it does not require multiplexing or a separate array of mixing channels. Furthermore, the gradient structure can be utilized in concert with cell experiments, to expose cells captured in microwells to various concentrations of soluble factors. We demonstrate the utility of this design to assess the viability of fibroblast cells in response to a range of hydrogen peroxide (H(2)O(2)) concentrations.     

Contact and edge effects in graphene devices

Electrical transport studies on graphene have been focused mainly on the linear dispersion region around the Fermi level and, in particular, on the effects associated with the quasiparticles in graphene behaving as relativistic particles known as Dirac fermions. However, some theoretical work has suggested that several features of electron transport in graphene are better described by conventional semiconductor physics. Here we use scanning photocurrent microscopy to explore the impact of electrical contacts and sheet edges on charge transport through graphene devices. The photocurrent distribution reveals the presence of potential steps that act as transport barriers at the metal contacts. Modulations in the electrical potential within the graphene sheets are also observed. Moreover, we find that the transition from the p- to n-type regime induced by electrostatic gating does not occur homogeneously within the sheets. Instead, at low carrier densities we observe the formation of p-type conducting edges surrounding a central n-type channel.     

Counterion effects in cyanine heterojunction photovoltaic devices

We investigated cyanine heterojunction photovoltaic devices using carbocyanine dyes as donors and buckminsterfullerene (C60) as acceptor. In particular, we focused on the influence of cyanine counterions on the photovoltaic device characteristics. It was found that counterions can be displaced in the applied electric field and give rise to important hystereses in the current-voltage characteristics, which are related to charge injection processes at electrode and organic heterointerfaces. Mobile counterions have also a drastic effect on the photocurrent spectrum and are responsible for an important C60 contribution at the organic heterojunction between cyanine and C60. If the counterion is covalently linked to the cyanine dye, the C60 contribution in the blue spectral domain can not be observed.     

Temperature relations inside bodies in nonlinear heat-conduction processes

An equation has been obtained which allows the unsteady temperature field inside multidimensional bodies to be calculated from known temperatures along the coordinate axes, in nonlinear heat-condition process.     

Use of nonlinear effects in engineering

The results of investigations into the use of effects produced with hydrodynamic oscillators for solution of certain engineering problems have been presented.     

On nonlinear effects in fracture mechanics

Linear elastic treatment of fracture is considered applicable for net section stress up to about 0.8 the uniaxial tensile yield stress. Crack front plastic yield is still small enough to be viewed and treated as a small perturbation to the local crack front elastic stress field.