在入射平面内小角度入射一维光栅零级衍射场的简便计算方法

耦合波分析法(RCWA)方法是目前研究光栅衍射最普遍的方法.垂直入射到光栅表面的光使衍射光的正负N级衍射波处于对称状态,使得在RCWA法中原先需要计算2N+1级衍射的2N+1阶矩阵问题降低到计算N+1级衍射的N+1阶矩阵问题.本文将这种对称结构的简化方法推广到非垂直入射、光栅条纹在入射平面内的情况,使得在这种耦合情况下...     

光诱导光学晶格中高斯型孤子的开关行为

讨论了高斯型空间光孤子在光折变介质光学晶格的传输行为,运用分步傅里叶变换法对传输方程进行数值分析.研究表明:单个斜入射高斯型光孤子在周期性光学晶格中会局限于入射波导传输或在合适振幅的情况下穿过若干波导再自陷于某个波导;而当同时存在正入射和斜入射孤子时,两者相遇后会发生反射或透射,并可通过斜入射光孤子的振幅选择反射或透射.     

入射光强对双光子亮屏蔽孤子相互作用的影响

通过数值模拟的方法,研究了入射光强对外加电场双光子光折变介质中两亮屏蔽孤子之间相互作用的影响.结果表明:在一定的入射光强范围内,同相孤子相互吸引,并伴随着融合现象,两孤子发生融合的作用距离随着入射光强的增加先增加而后减小;反相孤子相互排斥,排斥作用随入射光强的增加而减小,在某一特定值达到最小值,然后随着入射光强的增加而加大.当两孤子的相位差φ=π/2时,其相互作用过程中伴有能量转移,转移的能量与入射光强之间具有与排斥作用类似的非线性关系.     

嵌入式光栅多层结构锥形衍射的严格耦合波理论研究

基于严格耦合波分析理论,将嵌入式光栅多层结构平面衍射的理论模型扩展至锥形衍射的情况,可以模拟具有任意波长、偏振态、方位角和入射角的平面波入射该多层结构后形成的衍射。在此基础上,研究了微机械声光传感器锥形衍射中+1 级光衍射效率的收敛性。仿真表明:TM（Transverse Magnetic）偏振光入射且光栅周期为4 m 时,当谐波数M（2n+1）分别为67、69、71 时,+1级光衍射效率分别为28.86%、28.84%、28.86%,收敛性较好。另外,优化了微机械声光传感器的位移灵敏度,当入射角为22、方位角为10、光栅周期为1 m 时,与周期为4 m 的+1 级衍射光相比,TE、TM 偏振光入射时0、+1 级衍射光的位移灵敏度均提高一倍,可以准确地监测该传感器中声压或驱动电压引起的金属膜的位移。     

高散射介质后向散射模式的三级近似

生物组织是混浊介质,光在介质巾的传输主要是弹性散射[1].偏振光准直入射混浊介质表面,利用介质的多次后向散射偏振模式或Mueller矩阵的径向、方位变化的敏感性可确定介质的某些特性[2].如确定混浊悬浮液的粒子尺寸、浓度和各向异性因子;鉴别癌和非癌的细胞悬浮液体;确定介质的旋光特性等.     

艾里-高斯光束在光折变介质中的孤子脱落

以非线性薛定谔方程为理论模型,采用分步傅里叶方法研究了光折变介质中艾里-高斯光束的传输特性。结果表明:满足一定条件时,光折变介质中会形成周期振荡的空间孤子;介质的非线性系数越大,形成空间孤子所需的传输距离越短,孤子的振荡周期越小;当艾里-高斯光束的初始入射功率在一定范围内时,光折变介质中才会形成稳定的空间孤子;在空间孤子形成时,由于局部能量竞争,会出现光束分裂成丝现象。此外,还研究了微噪声扰动对艾里-高斯光束在光折变介质中传输稳定性的影响。     

激光波长对Ce:KNSBN晶体非线性特性的影响

采用非同时读出条件下晶体两波耦合实验装置,在相同的入射光参量下,研究了激光波长(λ)对Ce:KNSBN晶体两波耦合增益系数(r)、衍射效率(n)、响应时间及光扇效应入射光强度阈值的影响.结果显示,激光波长不同时,r、n,响应时间随光入射角2θ的演化趋势相同,但不同波长光入射时,对应相同的2θ,r、n及响应时间不同;激光波长不同时,Ce:KNSBN晶体中光扇效应的入射光强度阈值不同,λ为532nm时,阈值为38mW/cm2,λ为632.8nm时,阈值为26mW/cm2.     

厄米-高斯光束在饱和非线性介质中的传输特性

为了研究厄米-高斯光束在光折变饱和非线性介质中的传输特性,采用有限差分方法数值求解了光波演化方程,理论分析了厄米-高斯光束的传输特性。结果表明,1维1阶、2阶和3阶厄米-高斯光束在光折变非线性介质中传输时,在合适的非线性条件下,均可以形成呼吸模式的孤子;随着非线性的加大,厄米-高斯光束的光场分量之间的相互分离趋势将逐渐变弱,同时,每个光场分量的振幅起伏效应会更加明显;改变厄米-高斯光束的入射位置、入射角度对其传输特性没有影响;2维厄米-高斯光束的传输特性和1维情况是类似的。厄米-高斯光束的这些特性在光开关领域有一定的应用前景。     

椭圆偏振光谱测定α-Si的空位总体积分数

利用椭圆偏振光谱测得α-Si薄膜的有效介电函数,然后借助Webman等发展的、适用于四面体无定形半导体材料的有效介质理论,可以获得α-Si样品的总空位体积分数。按Webman的有效介质理论,经多次散射,光通过复介电函数分别为ε_1(λ),ε_2(λ),…,ε_i(λ),…,ε_n(λ)的n种介质组成的导质系统,有如下关系:     

Ce:KNSBN光折变光纤两波耦合特性研究

研究了掺铈钾钠铌酸锶钡(Ce:KNSBN)光折变光纤"扇"特性及两波耦合的基本特性.通过实验发现,当入射光的入射角为8°左右时,"扇"最小,这与块状晶体有根本的不同.在信号光与抽运光的入射夹角2θ小于11°时,两波耦合增益随入射夹角的增大而增大,而当入射夹角大于11°时,两波耦合增益随着入射夹角的增大而迅速减小.给出了在各个不同的入射夹角下,两波耦合增益中透射的信号光的时间特性曲线.两波耦合增益随信号-抽运比的增加而增加,在入射夹角为8°,信号-抽运比为1:1000时,两波耦合增益达到了77,比块状晶体相应条件下提高了4倍.用两波耦合的理论公式对增益随信号-抽运比的实验数据进行了拟合,二者相符.     

On the Dielectric Study of Se<Subscript>80−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>20</Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0, 1 and 2) Glasses

In the present paper, the dielectric parameters such as the dielectric constant ε′(ω), dielectric loss ε″(ω) and alternating current (ac) conductivity have been investigated for bulk amorphous chalcogenide Se_80?x Te₂₀Pb _x (x = 0, 1 and 2) glasses in the frequency range 10 Hz to 500 kHz and within the temperature range from 300 K to 320 K. Dielectric constant ε′(ω) and dielectric loss ε″(ω) are found to be highly frequency (ω) and temperature dependent, and this behavior is interpreted on the basis of Guintini’s theory of dielectric dispersion. The ac conductivity (σ _ac) is found to be temperature independent and obey the power law ω ^s , where s < 1 and decreases as temperature rises. The obtained results are discussed in terms of the correlation barrier hopping model proposed by Elliot. The composition dependence of the dielectric constant, dielectric loss and ac conductivity are also discussed and reported here.     

Electrical Conductivity and Dielectric Properties of Se85Te15−x Sb x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) Thin Films

The alternating-current (ac) conductivity and dielectric properties of Se₈₅Te_15?x Sb _x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) films are reported in this work. Thin films were deposited by thermal evaporation under base pressure of 10^?5 Torr. The films were well characterized by x-ray diffraction, differential scanning calorimetry, and energy-dispersive x-ray spectroscopy. The ac conductivity and dielectric properties have been investigated for the studied films in the temperature range from 297 K to 333 K and over the frequency range from 10² Hz to 10⁵ Hz. The experimental results indicate that the ac conductivity $ \sigma_{\rm{ac}} (\omega ) $ and the dielectric constant depend on temperature, frequency, and Sb content. The frequency dependence of $ \sigma_{\rm{ac}} (\omega ) $ was found to be linear with a slope lying very close to unity and is independent of temperature. This behavior can be explained in terms of correlated barrier hopping between centers forming intimate valence-alternation pairs. The density of localized states N(E _F) at the Fermi level is estimated. The activation energy $ \Updelta E(\omega ) $ was found to decrease with increasing frequency. The dielectric constant ε ₁ and dielectric loss ε ₂ were found to decrease with increasing frequency and increased with increasing temperature over the ranges studied. The maximum barrier height W _m for the studied films was calculated from an analysis of the dielectric loss ε ₂ according to the Guintini equation. The values agree with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The variation of the studied properties with Sb content was also investigated.     

Demonstration of a Dual-Band Mid-Wavelength HgCdTe Detector Operating at Room Temperature

In this paper, the performance of sequential dual-band mid-wavelength N⁺-n-p-p-P⁺-p-p-n-n⁺ back-to-back HgCdTe photodiode grown by metal-organic chemical vapor deposition (MOCVD) operating at room temperature is presented. The details of the MOCVD growth procedure are given. The influence of p-type separating-barrier layer on dark current, photocurrent and response time was analyzed. Detectivity without immersion D^* higher than 1 × 10⁸ cmHz^1/2/W was estimated for λ_Peak = 3.2 μm and 4.2 μm, respectively. A response time of τ_s ～ 1 ns could be reached in both MW1 and MW2 ranges for the optimal P⁺ barrier Cd composition at the range 0.38–0.42, and extra series resistance related to the processing R_Series equal to 500 Ω.     

Electrical and dielectric properties of chromotrope 2R in pellet and thin film forms

The dark conductivity (dc and ac) and dielectric properties of chromotrope 2R (CHR) in pellet as well as in thin film forms have been investigated as function of frequency (100 Hz to 5 MHz) within the temperature range (293–423 K). The ac conductivity of CHR pellet in sandwich structure employing two symmetrical gold ohmic contacts shows both temperature and frequency dependence with relatively stronger dependence in the higher temperature and lower frequency ranges respectively. It is found that σ_ac(ω) obey Jonscher’s universal power law, σ_ac(ω) = Aω^s with s < 1 and the results has been analyzed with reference to various theoretical models. The correlated barrier hopping model (CBH) with single polaron process is found to be the dominant conduction mechanism for charge carrier transport in CHR material within the investigated temperature range. The dc conductivity has been measured in the considered temperature range for as deposited and annealed films. The results are fitted to Arhenius equation and the activation energy has been deduced at different frequencies. The results showed also that heating the deposited CHR films may reveal films with more stable electrical properties. Moreover, both the dielectric constant ε₁ and the dielectric loss ε₂ are found to increase with temperature and decrease with frequency which reveal that the CHR samples exists in molecular dipole form. The behavior of ε₂ as a function of both frequency and temperature is analyzed according to Giuntini et al. model.     

Good Thermal Stability,High Permittivity,Low Dielectric Loss and Chemical Compatibility with Silver Electrodes of Low-Fired BaTiO<Subscript>3</Subscript>–Bi(Cu<Subscript>0.75</Subscript>W<Subscript>0.25</Subscript>)O<Subscript>3</Subscript> Ceramics

(1 ? x)BaTiO₃–xBi(Cu_0.75W_0.25)O₃ [(1 ? x)BT–xBCW, 0 ≤ x ≤ 0.04] perovskite solid solutions ceramics of an X8R-type multilayer ceramic capacitor with a low sintering temperature (900°C) were synthesized by a conventional solid state reaction technique. Raman spectra and x-ray diffraction analysis demonstrated that a systematically structural evolution from a tetragonal phase to a pseudo-cubic phase appeared near 0.03 < x < 0.04. X-ray photoelectron analysis confirmed the existence of Cu⁺/Cu²⁺ mixed-valent structure in 0.96BT–0.04BCW ceramics. 0.96BT–0.04BCW ceramics sintered at 900°C showed excellent temperature stability of permittivity (Δε/ε _25°C ≤ ±15%) and retained good dielectric properties (relative permittivity ～1450 and dielectric loss ≤2%) over a wide temperature range from 25°C to 150°C at 1 MHz. Especially, 0.96BT–0.04BCW dielectrics have good compatibility with silver powders. Dielectric properties and electrode compatibility suggest that the developed materials can be used in low temperature co-fired multilayer capacitor applications.     

Low power flexible organic thin film transistors with amorphous Ba0.7Sr0.3TiO3 gate dielectric grown by pulsed laser deposition at low temperature

We deposited amorphous Ba_0.7Sr_0.3TiO₃ (BST) on silicon and plastic substrate under 110 °C by pulsed laser deposition (PLD) and use it as the dielectric of the organic transistor. Depends on the thickness of BST layer, the highest mobility of the devices can achieve 1.24 cm² V^?1 s^?1 and 1.01 cm² V^?1 s^?1 on the silicon and polyethylene naphthalate (PEN) substrate, respectively. We also studied the upward and downward bending tests on the transistors and the dielectric thin films. We found that the BST dielectric pentacene transistor can maintain the mobility at 0.5 cm² V^?1 s^?1 or higher while the bending radius is around 3 mm in both upward and downward bending. Our finding demonstrates the potential application of PLD growth high-k dielectric in the large area organic electronics devices.     

Reliability of a connected-(r1, s1)-or-(r2, s2)-or-..-or-(rk, sk)-out-of-(m,n): F lattice system

A (linear or circular) connected-(r₁, s₁)-or-(r₂, s₂)-or-^{. .}-or-(r_k, s_k)-out-of-(m, n): F lattice system is the (linear or circular) (m, n)-lattice system if the system fails whenever all components in a connected-(r₁, s₁)-submatrix or all components in a connected-(r₂, s₂)-submatrix or ^{. .} or all components in a connected-(r_k, s_k)-submatrix fail. This paper presents a recursive algorithm for the reliability of the (linear or circular) connected-(r₁, s₁)-or-(r₂, s₂)or-^{. .}-or-(r_k,s_k)-out- of-(m, n):F lattice system. The recursive algorithm requires time and time in the linear case and the circular case, respectively Furthermore, we can reduce the more computing time in the statistically independent and identically distributed case or considering some special systems. Especially, the closed formula is given for the reliability of the linear connected-(2, 1)-or-(1, 2)-out-of-(m, 2): F lattice system in the statistically independent and identically distributed case.     

Polarization characteristics of surface plasmon resonance in SnO<Subscript>2</Subscript> nanocluster films

Internal reflection features caused by the surface plasmon resonance in nanoscale films containing defect tin dioxide clusters in the stoichiometric dielectric matrix are studied by the method of polarization modulation of electromagnetic radiation. The angular and spectral characteristics of reflectances R _s ² and R _p ² of s- and p-polarized radiation and their polarization difference ρ = R _s ² − R _p ² are measured in the wavelength range λ = 400–1600 nm. The experimental characteristics ρ(ϑ, λ) (ϑ is the radiation incidence angle) obtained represent the optical property features associated with the film structure and morphology. Surface plasmon polaritons and local plasmons excited by s- and p-polarized radiation are detected; their frequency and relaxation properties are determined. The structural sensitivity of the technique for studying the surface plasmon resonance for tin dioxide films is shown.     

Electromagnetic characterization of ceramic material produced with natural zeolite

The aim of this study is to investigate the electromagnetic characterization of ceramic panel produced with natural zeolite via considering the frequency-dependent transmission (T), reflection (R) and absorption (A) coefficients. For this purpose, first of all, frequency-dependent complex dielectric values(dielectric permittivity and tangent loss) of material are measured via LCR meter and complex dielectric values used in three dimensional(3D) electromagnetic simulation tool. Then, Debye parameters such as static permittivity(ε_s), optic permittivity(ε_∞) and relaxation time(τ) are derived by using genetic algorithms. Finally, to validate the simulation results, T, R and A coefficients obtained from simulations are compared with frequency-dependent T, R and A values calculated by using the transmission-line equation.     

Layered Sb2Te3 Nanoflakes as Chalcogenide Dielectrics

Dielectric nanoflakes of Sb₂Te₃ represent an important advance in science and technology due to their extraordinary properties. Polycrystalline layered Sb₂Te₃ nanoflakes have been successfully synthesized via a high-throughput chemical route at 60°C. The frequency and temperature dependence of the dielectric constant and dielectric loss of the layered Sb₂Te₃ nanoflakes have been measured in the frequency range from 30 Hz to 758,000 Hz and temperature range from 313 K to 373 K. As-synthesized Sb₂Te₃ nanoflakes are shown to be promising alternative dielectrics because of their high dielectric constant (ε′ ≈ 7.3 to 6022) and low dielectric loss (tan δ ≈ 0.2 to 9.2). These higher values of ε′ and lower values of tan δ of Sb₂Te₃ nanoflakes confirm that capacitors with capacity (C) of ～5.2 pF to 4336 pF may be fabricated for storing renewable energy. Raman spectroscopy confirms that the peak located at ～142 cm^?1 corresponds to one in-plane vibrational mode (E _g ² ) of layered Te–Sb–Te–Sb–Te lattice vibration.