混沌介质光学常数测量

对基于漫射理论并应用CCD相机测量混沌介质的光学常数进行了实验研究.提出采用漫射中心环带约束法来提高逆向求解光学常数的精确性,以及采用在通过光的入射点和漫射中心的直线上截取一维原始数据的方法来提高算法的计算效率.以Intralipid脂肪乳剂作为混沌介质,对方法进行了实验验证.结果表明,本文提出的方法是可行的.     

合金钢材料光学常数的椭偏测量及其修正

用椭偏法测量了入射光波长0.632μm、入射角50°至85°时某合金钢的光学常数。考虑材料表面的粗糙度,用Ohlidal-Lukes理论对所测光学常数值进行修正,发现椭偏参量的修正量随入射角增大而增大。结果表明,用椭偏法测量合金钢光学常数时采用较小入射角能获得更精确的样片光学常数。     

椭偏法测量表面微粗糙合金钢材料的光学常数研究

采用椭偏法测量入射光波长为0.632μm,入射角为50°～85°时合金钢的光学常数。考虑材料表面的粗糙度,用Ohlidal-Lukes理论对所测光学常数值进行了修正,发现椭偏参量的修正量随入射角增大而增大。结果表明,测量入射角在50°～70°范围内测量值与修正后计算结果基本一致,在70°～85°范围内测量值与修正后的计算结果差距较大。因此,用椭偏法测量合金钢光学常数时使入射角小于70°,测量结果会更加准确。     

反射光谱包络线法测量光电薄膜的光学常数和厚度

提出了一种利用薄膜反射光谱包络线法计算光电薄膜光学常数和厚度的方法。当一束光照射在基板上的介质膜上时,由于薄膜上、下界面反射光的相干,会使反射光谱的曲线有一定的波动。本文对反射光谱进行了理论分析,给出计算公式,从测量曲线中的实验值得出薄膜的厚度和光学常数。此种方法计算过程简单、迅速,而且易于编程处理。     

采用椭偏法结合分光光度法研究极薄银的光学常数

极薄银在滤光片、高反射镜等中有广泛的应用,其光学常数严重影响着膜系的特性。在室温条件下,采用电阻热蒸发技术分别在硅和玻璃基底上沉积5.3 nm~26 nm不同厚度的极薄银薄膜,用TalySurfCCI非接触式轮廓仪测量了薄膜的厚度,研究了不同厚度银薄膜的光学常数n和k。镀制厚度5.3 nm、7.9 nm、14.1 nm、26.0 nm的银薄膜,结果显示极薄银的光学常数与块状银光学常数不同,当膜厚小于14.1 nm时,折射率n在380 nm~600 nm随波长增加而增加,在600 nm~1 600 nm随波长增加缓慢减小至趋于稳定值2.6;消光系数k在380 nm~500 nm随着波长增加而增加,在500 nm~1 600 nm随波长增加而缓慢减小至趋于0不变;当膜厚大于14.1 nm时,折射率随波长增加而增加,消光系数随波长近似呈线性增加。整体上,膜厚增加时折射率减小且趋于块状银的折射率,k随厚度增加而增加并最终趋于块状膜。用此拟合的光学常数代入TFc膜系设计软件计算其透射率,发现与分光光度计测得的透射率吻合较好。     

梯度颗粒复合介质的光学双稳

重点研究了组分的梯度构形对带壳球形颗粒复合介质的光学双稳特性的影响.其中球形颗粒是由非线性核和介电函数具有梯度分布的线性壳组成.对于壳层介电函数具有幂指数分布的情况,通过求解麦克斯韦方程,得到各区域的势能分布函数,从而求得核内电场的数学表达式.数值研究发现,该复合介质的光学双稳阈值和区域与壳层的厚度及壳层的介电幂指数有关,随着壳层厚度增大或幂指数增大,双稳阈值将变宽.此外,还研究了正入射情况下复合材料体系的反射系数随外电场的变化情况, 发现其关系曲线是一条回线. 关键词： 梯度颗粒 复合介质 光学双稳     

光学弱相干反射测量系统频谱分析

本文在弱物体近似下从成象系统角度研究了光学弱相干反射测量术,分析了该技术测量时信号的形成机理.结果表明它相当于一线性平移不变系统,具有高通滤波特性,直接测量的是缺陷分布的高频信息.本文的工作为定量分析测量结果及进一步提高空间分辨率提供了理论依据.     

两种反射法确定光学常数的非单值性的研究

Darcie-Whalen反射法确定光学常数是多值的并且计算图面积只有72％，它与Owen的分类法中具有单值的且计算图面积为100％的H法相比具有较小的灵敏度。     

椭偏与光度法联用精确测定吸收薄膜的光学常数与厚度

介绍了一种同时利用椭偏仪和分光光度计精确测量薄膜光学常数的方法, 并详细比较了该方法与使用单一椭偏仪拟合结果的可靠性.采用可变入射角光谱型椭偏仪（VASE）表征了250—1700 nm波段辉光放电法沉积的类金刚石薄膜,研究发现当仅用椭偏参数拟合时,由于厚度与折射率、消光系数的强烈相关性,无法得到吸收薄膜光学常数的准确解.如果加入分光光度计测得的透射率同时拟合,得到的结果具有很好的惟一性.该方法无需设定色散模型即可快速拟合出理想的结果,特别适合于确定透明衬底上较薄吸收膜的光学常数. 关键词： 光学常数 光谱型椭偏仪 吸收薄膜 透射率     

Velocity autocorrelation spectra of fluid in porous media measured by the CPMG sequence and constant magnetic field gradient

Carr-Purcell-Meiboom-Gill (CPMG) train of radiofrequency pulses applied to spins in the constant magnetic field gradient is an efficient variant of the modulated magnetic field gradient spin echo method, which provides information about molecular diffusion in the frequency domain instead of in the time domain as with the two-pulse gradient spin echo. The frequency range of this novel technique is broad enough to sample the power spectrum of displacement fluctuation in water-saturated pulverized silica (SiO2) and provides comprehensive information about the molecular restricted motion as well as about the structure of the medium.     

以物像等大成像法同时测量自聚焦透镜的轴心折射率n_0和聚焦常数g

本文通过对目前自聚焦透镜光学参数测量方法的分析,提出了能同时测量自聚焦透镜轴心折射率n_0和聚焦常数(二次梯度常数)g的物像等大法,所得结果表明该方法有实用价值,同时可简化测量设备。     

A canonical relativistic approach to quantize electromagnetic field in the presence of moving magneto-dielectric media

A canonical relativistic formulation is introduced to quantize electromagnetic field in the presence of a polarizable and magnetizable moving medium. The medium is modeled by a continuum of the second rank antisymmetric tensors in a phenomenological way. The covariant wave equation for the vector potential and the covariant constitutive equation of the medium are obtained as the Euler-Lagrange equations using the Lagrangian of the total system. A fourth rank tensor which couples the electromagnetic field and the medium is introduced. The susceptibility tensor of the medium is obtained in terms of this coupling tensor. The noise polarization tensor is calculated in terms of both the coupling tensor and the ladder operators of the tensors modeling the medium.     

Spectral characterization of diffusion in porous media by the modulated gradient spin echo with CPMG sequence

Carr-Purcell-Meiboom-Gill train of radiofrequency pulses applied to spins in the constant magnetic field gradient is an efficient variant of the modulated magnetic field gradient spin echo method, which provides information about molecular diffusion in the frequency-domain instead in the time-domain as with the two-pulse gradient spin echo. The frequency range of novel technique is broad enough to sample the power spectrum of displacement fluctuation in water-saturated pulverized silica (SiO(2)) and provides comprehensive information about the molecular restricted motion as well as about the structure of medium.     

Optical properties and temperature dependence of critical transitions in ZnSe

The dielectric function of ZnSe has been deduced from ellipsometric measurements between 20 K and 380 K. is analysed around each critical point with the standard critical point model. The variations of the different parameters characterising each transition with temperature are presented and analysed. The temperature coefficients of the energies of the critical transitions are given. is essentially governed by the Coulomb interaction near the fundamental gap. Thanks to the high binding energy of the exciton and the low spectral width of the ellipsometer, the fundamental state of the exciton is found completely separated from the first excited states and the continuum at low temperature. In return the strong transition E₁ near the L points of the Brillouin zone can be described equally well with a 2D or an excitonic transition. Received 5 February 1999 and Received in final form 15 June 1999     

Synthesis of large diamond crystals containing high-nitrogen concentration at high pressure and high temperature using Ni-based solvent by temperature gradient method

This paper reprots that with Ni-based catalyst/solvent and with a dopant of NaN 3,large green single crystal diamonds with perfect shape are successfully synthesized by temperature gradient method under high pressure and high temperature in a China-type cubic anvil high-pressure apparatus (SPD-6×1200),and the highest nitrogen concentration reaches approximately 1214-1257 ppm calculated by infrared absorption spectra.The synthesis conditions are about 5.5 GPa and 1240-1300 C.The growth behaviour of diamond with high-nitrogen concentration is investigated in detail.The results show that,with increasing the content of NaN 3 added in synthesis system,the width of synthesis temperature region for growth high-quality diamonds becomes narrower,and the morphology of diamond crystal is changed from cube-octahedral to octahedral at same temperature and pressure,the crystal growth rate is slowed down,nevertheless,the nitrogen concentration doped in synthetic diamond increases.     

Solution of near-field thermal radiation in one-dimensional layered media using dyadic Green's functions and the scattering matrix method

A general algorithm is introduced for the analysis of near-field radiative heat transfer in one-dimensional multi-layered structures. The method is based on the solution of dyadic Green's functions, where the amplitude of the fields in each layer is calculated via a scattering matrix approach. Several tests are presented where cubic boron nitride is used in the simulations. It is shown that a film emitter thicker than 1 μm provides the same spectral distribution of near-field radiative flux as obtained from a bulk emitter. Further simulations have pointed out that the presence of a body in close proximity to an emitter can alter the near-field spectrum emitted. This algorithm can be employed to study thermal one-dimensional layered media and photonic crystals in the near-field in order to design radiators optimizing the performances of nanoscale-gap thermophotovoltaic power generators.     

Ultrasonic distance and velocity measurement using a pair of LPM signals for cross-correlation method: improvement of Doppler-shift compensation and examination of Doppler velocity estimation

Real-time distance measurement of a moving object with high accuracy and high resolution using an ultrasonic wave is difficult due to the influence of the Doppler effect or the limit of the calculation cost of signal processing. An over-sampling signal processing method using a pair of LPM signals has been proposed for ultrasonic distance and velocity measurement of moving objects with high accuracy and high resolution. The proposed method consists of cross correlation by single-bit signal processing, high-resolution Doppler velocity estimation with wide measurement range and low-calculation-cost Doppler-shift compensation. The over-sampling cross-correlation function is obtained from cross correlation by single-bit signal processing with low calculation cost. The Doppler velocity and distance of the object are determined from the peak interval and peak form in the cross-correlation function by the proposed method of Doppler velocity estimation and Doppler-shift compensation. In this paper, the proposed method of Doppler-shift compensation is improved. Accuracy of the determined distance was improved from approximately within ±140 μm in the previous method to approximately within ±10 μm in computer simulations. Then, the proposed method of Doppler velocity estimation is evaluated. In computer simulations, accuracy of the determined Doppler velocity and distance were demonstrated within ±8.471 mm/s and ±13.87 μm. In experiments, Doppler velocities of the motorized stage could be determined within ±27.9 mm/s.     

Effect of spontaneously generated coherence on EIT and its refractive properties in four- and five-levels systems

The effects of spontaneously generated coherence (SGC) and phases of optical fields on the phenomenon of electromagnetically induced transparency (EIT) are investigated in a four-level inverted-Y system and in a five-level K-type system under various parametric conditions in order to demonstrate controllability of the EIT, dispersion properties, and group velocity in such systems. Non-zero second-order susceptibility in both systems is due to the SGC effect. The experimental viability of the model in semiconductor quantum well systems is also discussed.     

Monte Carlo simulation of photon migration path in turbid media

A new method of Monte Carlo simulation is developed to simulate the photon migration path in a scattering medium after an ultrashort-pulse laser beam comes into the medium.The most probable trajectory of photons at an instant can be obtained with this method.How the photon migration paths are affected by the optical parameters of the scattering medium is analyzed.It is also concluded that the absorption coefficient has no effect on the most probable trajectory of photons.