Single channel tunable wavelength demultiplexer using nonlinear one dimensional defect mode photonic crystal

Transmission characteristics of nonlinear one dimensional photonic crystal with a defect have been studied. GaAs/Si multilayer structure with a single defect has been simulated using transfer matrix method. In this study refractive indices of both layers have been taken to be dependent on intensity and wavelength simultaneously. It is found that central wavelength of defect mode change with intensity of wave. Average change in central wavelength of defect mode is 0.02 nm/(1 GW/cm²). This property can be exploited in the design of a single channel tunable wavelength division demultiplexer for optical communication.     

Qualitative analysis and traveling wave solutions for the perturbed nonlinear Schrödinger's equation with Kerr law nonlinearity

In this Letter, we investigate the perturbed nonlinear Schrödinger's equation (NLSE) with Kerr law nonlinearity. All explicit expressions of the bounded traveling wave solutions for the equation are obtained by using the bifurcation method and qualitative theory of dynamical systems. These solutions contain bell-shaped solitary wave solutions, kink-shaped solitary wave solutions and Jacobi elliptic function periodic solutions. Moreover, we point out the region which these periodic wave solutions lie in. We present the relation between the bounded traveling wave solution and the energy level h. We find that these periodic wave solutions tend to the corresponding solitary wave solutions as h increases or decreases. Finally, for some special selections of the energy level h, it is shown that the exact periodic solutions evolute into solitary wave solution.     

光在非均匀介质中传播规律的演示

光在介质中的传播规律遵循费马原理,如：在均匀介质中,光沿直线传播．在非均匀介质中,光的传播轨迹比较复杂,与非均匀介质的状态有密切关系．尽管海市蜃楼和沙漠幻影是大自然中能够看到的光在非均匀介质中的传播现象,但只有在一定条件下才能出现,不是随时可以看到的．为了能在光学教学中让学生能够看到光在非均匀介质中的传播,本文利用白糖溶液和水之间扩散形成的浓度非均匀区域,实现了光线的非直线传播．通过光线实际传播的路径,计算了非均匀区域液体折射率的相对变化．这一演示实验取材简单,容易实现,对学生思维训练具有一定的借鉴意义．     

激发介质相对不应态对螺旋波动力学行为的影响

采用元胞自动机模型研究激发介质相对不应态对螺旋波动力学行为的影响。数值模拟表明：元胞激发阈值存在一临界区间,该区间的螺旋波周期会突然增加,并存在一最大周期,在合适的系统尺寸和状态数下,螺旋波周期不再受相对不应态的影响而只取决于系统的激发阈值;相对不应态导致螺旋波“Z”型漫游、小范围无规律漫游、花瓣状漫游、锯齿状漫游、风车状漫游等复杂的波头运动。观察到稳定螺旋波、漫游螺旋波和螺旋波消失,并对产生这些现象的机制作简要的解释。     

聚合物载体中水杨酸晶体的太赫兹极化率测定

极化率作为材料的重要微观属性,与其呈现出的多种宏观属性等紧密相关,在新型药物及功能材料的设计中扮演着关键角色.对于微观结构存在复杂分子间作用的物质体系,获取其太赫兹波段的动态极化率具有重要意义.极化率的实验测定建立在其本征介电常数的准确测定之上,太赫兹时域光谱系统凭借其相干探测属性,可直接提供太赫兹波在穿透样品后的相位...     

Magnetohydrodynamic flow and heat transfer of a hybrid nanofluid over a rotating disk by considering Arrhenius energy

This research work explores the effect of hybrid nanoparticles on the flow over a rotating disk by using an activation energy model. Here, we considered molybdenum disulfide and ferro sulfate as nanoparticles suspended in base fluid water. The magnetic field is pragmatic normal to the hybrid nanofluid flow direction. The derived nonlinear ordinary differential equations are nondimensionalized and worked out numerically with the help of Maple software by the RKF-45method. The scientific results for a non-dimensionalized equation are presented for both nanoparticle and hybrid nanoparticle case. Accoutrements of various predominant restrictions on flow and thermal fields are scanned. Computation estimation for friction factor, local Nusselt number and Sherwood number are also executed. Results reveal that the reduction of the heat transfer rate is greater in hybrid nanoparticles when compared to nanoparticles for increasing values of Eckert Number and the thermal field enhances for the enhanced values of volume fraction.     

Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization

A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.     

Thickness induced magnetic anisotropic properties of Tb-Fe-Co thin films

The influence of Tb₂₅Fe₆₁Co₁₄ thin film thicknesses varying from 2 to 300 nm on the structural and magnetic properties has been systematically investigated by using of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetization, and magneto-optic Kerr effect microscopy measurements. Thin film growth mechanism is pursued and controlled by ex-situ X-ray refractometry measurements. X-ray diffraction studies reveal that the Tb₂₅Fe₆₁Co₁₄ films are amorphous regardless of thin films thicknesses. The magnetic properties are found to be strongly related to thickness and preferred orientation. With an increase in film thickness, the easy axis of magnetization is reversed from in-plane to out-of-plane direction. The change in the easy axes direction also affects the remanence, coercivity and magnetic anisotropy values. The cause for the magnetic anisotropy direction change from in-plane to out-of-plane can be related to the preferred orientation of the thin film which depends on the large out-of-plane coercivity and plays an important role in deciding the easy axes direction of the films. According to our results, up to the 100 nm in-plane direction is dominated over the whole system under major Fe-Fe interaction region, after that point, the magnetic anisotropy direction change to the out-of-plane under major Tb-Fe/Tb-Co interaction region and preferred orientation dependent perpendicular magnetic anisotropic properties become more dominated with 2.7 kOe high coercive field values.     

Magnetic line source diffraction by a conductive half-plane in an anisotropic plasma

An integral theory that is associated with the scattered fields is considered for the solution of H-polarized line source diffraction by a conductive half-plane, which is surrounded by an anisotropic plasma. As the anisotropy does not affect an E-polarized incident wave, only one polarization case is considered. The cold plasma medium is characterized by the dielectric tensor. The constant external magnetic field producing the anisotropy in a cold plasma is applied parallel to the edge of the half-plane. The total, scattered, and diffracted waves are derived in terms of the Fresnel functions. Therefore, finite magnitude values at the transition boundaries are obtained. The wave behaviours are investigated numerically for different quantities of the medium.     

Parametric study of plasma active medium and gain saturation region in a Ne-like soft X-ray laser

Plasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X-ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X-ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double-pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne-like germanium soft X-ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X-ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X-ray laser intensity with 294 cm⁻¹ gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium.