Measurement of birefringence for optical recording of disk substrates

We experimentally investigate the birefringence of bare and coated substrates for magneto-optical recording, using ellipsometry at wavelengths of 632.8 and 780 nm. The polarization rotation and ellipticity of reflected or transmitted light are measured for different incident angles and for different orientations of the incident linear polarization. The measured data are then fitted by the MULTILAYER computer program, which solves the Maxwell equations for a plane wave propagating in a multilayer structure. This approach makes it possible to determine, with high accuracy, the orientations of the principal axes of the substrate and the corresponding refractive indices. The results show that one of the principal axes is always along the substrate's normal direction, but the orientations of the in-plane principal axes can be much different from the radial and track directions. A special feature of the ellipsometers that were used is that a glass hemisphere is placed in contact with the substrate to eliminate refraction of the incident beam. This enables a maximum propagation angle of 70° (with respect to the normal) in the substrate and hence increases the measurement sensitivity. Certain anomalies have been observed, which we believe are associated with the variation of birefringence properties along the thickness direction.     

Simple birefringence measurement method for coated optical disks with a fixed incident angle ellipsometer

In a coated and laminated optical disk, only a reflectance method is available for oblique incidence retardation measurements to evaluate the birefringence in a polycarbonate substrate. I propose a simple measurement method that simultaneously measures both the lateral and vertical birefringence in a coated substrate. In this reflectance method, only two oblique incidence retardation values with a fixed incident angle are measured from the radial and the circumferential directions of the disk. Using the sum and the difference of these two retardation values, we can calculate both birefringences without any cumbersome curve-fitting procedure. This method can easily be introduced into the routine inspection for optical disk manufacturing.     

Anisotropic scatter patterns and anomalous birefringence of obliquely deposited cerium oxide films

Cerium oxide films formed by electron-beam evaporation onto oblique substrates are shown to scatter light strongly into spatially anisotropic distributions and to exhibit large normal-incidence birefringence Δ n = n(s) - n(p). The apparatus for direct recording of a useful projection of the scatter distributions is described. Characteristic differences in scatter patterns recorded for cerium oxide, relative to those from tilted columnar titania and zirconia films, are believed to be associated with unusual microstructures recorded for cerium oxide films by scanning electron microscopy. With increasing angle of deposition, the microstructure of cerium oxide was observed to change from densely packed columns to partially isolated needlelike columns at angles that do not obey the tangent rule. In particular, deposition at 55° yielded columns nearly perpendicular to the substrate, yet the normal-incidence birefringence was large. The retardation of the films was recorded as a function of angle of incidence for propagation in the deposition plane. A turning point near 0° incidence for the 55° film confirmed that one principal axis is perpendicular to the substrate. Significant bunching of columns into rows running perpendicular to the deposition plane was recorded by scanning electron microscopy and may account for both the scatter and the birefringence.     

Angle-dependent light emission from aligned multiwalled carbon nanotubes under CO(2) laser irradiation

This paper reports the light emission from aligned multiwalled carbon nanotubes (MWNTs) under continuous wave CO(2) laser (λ = 10.6?μm) irradiation. Results indicate that the light emission is dependent on the angle θ between the laser incident direction and the nanotube axis. The relative intensity of the light emission at certain wavelengths shows a Lorentzian feature when θ varies from 0° to 90°. The Lorentzian fitting curve displays a distinct tendency between shorter (λ<600?nm) and longer wavelength (λ>700?nm). A minimum intensity was observed at θ(m) close to 67° under shorter wavelength, whereas a maximum intensity was shown at θ(m) of about 60° at longer wavelength. These results show the anisotropic property of aligned MWNTs.     

Anisotropic optical properties of ZnS thin films with zigzag structure

ZnS sculptured thin films produced by thermal evaporation method using the glancing angle deposition technique at different deposition angles (0, 30, 60, 70 and 80\({^{\circ }}\)) are reported. The structural and optical properties of the prepared samples are investigated systematically using X-ray diffraction (XRD) and UV–VIS spectroscopy techniques. The XRD studies show cubic structure for the prepared films and deposition angle dependence of lattice constants, intrinsic stress, tensile stress and dislocation density. The obtained transmittance spectra in the range 380–850 nm for both s- and p-polarized light at normal incidence angle are used to study the s- and p-refractive indices and in-plane birefringence of the ZnS films. The maximum birefringence is evaluated at incident flux angle \(\alpha = 70{^{\circ }}\). Both the refractive index and packing density of the films decrease with increasing deposition angle, which confirm the structural inhomogeneity and porosity nature of the films.     

Design of a general point focusing crystal geometry for x-ray spectroscopy

A nearly exact general equation for geometrical angular deviations from the Bragg angle over entire curved crystal surfaces is derived using a toroidally curvilinear coordinate system and applied on the nine conventional crystal geometries. Although the derived formula confirms Wittry's results for the first five cases, it shows considerable differences for the more important cases, such as 45° point focusing, general point focusing, and Berreman geometries. The effective scattering areas for the mentioned cases have been derived, plotted, and interpreted. A point-to-point focusing crystal geometry is introduced, and it is shown that it approaches Wittry's and spherical plane-spherical Johansson geometries as θ(B) → 90° and θ(B) → 0°, respectively.     

Optimization of periodic column growth in glancing angle deposition for photonic crystal fabrication

We investigate the growth of periodically aligned silicon microstructures for the fabrication of square spiral photonic crystals using the glancing angle deposition phi-sweep process. We report the optimization of the phi-sweep offset angle for fabrication of microstructures with more precise geometry. The effects of varying the sweep offset angle of the phi-sweep process are studied for films deposited onto a square lattice array of growth seeds. To represent one growth segment of the phi-sweep process, we fabricate 15?nm silicon thin films using several azimuthal substrate offsets from 0° to 45° at a vapor incidence angle of 85°. We also deposit silicon square spirals on square lattice arrays with the phi-sweep method, using various sweep offset angles from γ = 0° to 45°. We find that using an offset angle of γ = 26.5° optimizes the shadowing geometry, which minimizes anisotropic broadening, producing greater quality photonic crystal structures. From normal incidence reflection spectroscopy, a maximum full width at half-maximum of 273 ± 3?nm and a relative peak width (Δλ/λ) of 16.1 ± 0.1% were found for a sweep offset angle of γ = 26.5°.     

二色调相式双折射系统的设计及其应用

以二色氩离子激光作光源,采用相调制技术设计了用于同时实时测量流场双折射及取向角的二色调相式流动双折射实验装置。由于采用了二色光源,避免了在计算过程中运用二阶贝塞尔函数以及在信号处理时分析二次谐波,简化了实验装置及结果计算。装置通过低通滤波电路和锁相放大器分别测量入射光和出射光中基频成分的光强度,并把它们转换成数字信号,由此计算出待测流场的双折射和取向角。实验证明,应用该装置同步测量了双折射及取向角,最大测量误差控制在0.5%~1%。     

Dispersion of linearly polarized light propagating in a thin birefringent plate

We analyze theoretically the dispersion of linearly polarized light propagating in a uniaxial anisotropic medium where multibeam interference is present. Explicit expressions of the group-delay dispersion for transmitting waves are derived for the simplest situation, and the effect of dispersion on pulse broadening is analyzed for a few selected cases. Our results reveal that at normal incidence and in the situation where the optic axis is parallel to the surface of birefringent plate (in the x-y plane), the dispersion of the refracted wave decreases with the extent of birefringence. In particular, the dispersion for the electric field parallel to the polarization direction of the incident light changes with the rotation angle between the optic axis and the polarization direction of the incident field, whereas the dispersion for the refracted field whose direction is vertical to the polarization of incident light is independent of this angle. For oblique incidence, dispersion varies substantially for different incident angles. In the situation where the optic axis is in the x-z plane at either normal or oblique incidence, the dispersion increases in a periodically oscillating manner as a function of the relative thickness of the birefringent plate.     

Fluidic actuation of an elastomeric grating

A fluidic chamber with an elastomeric grating membrane is fabricated. Grating groove spacing is modified through membrane deformation via fluid injection. Tunable diffraction output is demonstrated. At normal incidence, the diffraction angle changes by 14.2° and 9.8° for incident wavelengths 632.8 and 488?nm, respectively, with an injected fluid volume of 1?ml.     

Analysis of a Fibre-optic Ring Resonator with Polarization Effects: Application to Polarization Sensing with Improved Sensitivity

Abstract

A theoretical analysis for a fibre-optic ring resonator is given by assuming a polarization modulation in the loop fibre. If the change in polarization angle θ in the loop is large, the output intensity has two resonance dips separated in phase by an angle equal to 2θ, when the loop phase is scanned from 0 to 2π. When θ is small, the resonator output produces only one resonance dip and the amplitude of this resonance dip is a measure of θ. By placing a polarizer at the resonator output, a resonance peak in the intensity is produced with an amplitude that increases with increasing θ. Such a system has potential applications, for example, in Faraday current sensing, with an increased sensitivity. The effects of birefringence in the loop and the angle of polarization of the input light are also analysed.     

Determination of retardation parameters of multiple-order wave plate using a phase-sensitive heterodyne ellipsometer

To characterize the linear birefringence of a multiple-order wave plate (MWP), an oblique incidence is one of the methods available. Multiple reflections in the MWP are produced, and oscillations in the phase retardation measurement versus the oblique incident angle are then measured. Therefore, an antireflection coated MWP is required to avoid oscillation of the phase retardation measurement. In this study, we set up a phase-sensitive heterodyne ellipsometer to measure the phase retardations of an uncoated MWP versus the oblique incident angle, which was scanned in the x-z plane and y-z plane independently. Thus, the effect on multiple reflections by the MWP is reduced by means of subtracting the two measured phase retardations from each other. As a result, a highly sensitive and accurate measurement of retardation parameters (RPs), which includes the refractive indices of the extraordinary ray n(e) and ordinary ray n(o), is obtained by this method. On measurement, a sensitivity (n(e),n(o)) of 10(-6) was achieved by this experiment setup. At the same time, the spatial shifting of the P and S waves emerging from the MWP introduced a deviation between experimental results and the theoretical calculation.     

Effects of substrate birefringence and tilt on the irradiance and phase patterns of the return beam in magneto-optical disk data storage

Substrate birefringence in a magneto-optical disk system is shown to have a predictable effect on the return beam. The irradiance and phase patterns of the return beam at the exit pupil of the objective lens are calculated and experimentally verified for the cases of no substrate birefringence, birefringence aligned with the incident polarization, and birefringence aligned at 45° to the incident polarization. The irradiance at the exit pupil is also calculated (and experimentally verified) for a grooved substrate for various amounts of substrate tilt.     

Incident angle effect of the primary beam upon the mean depth of electrons in a target

When a target is bombarded by a mono-energetic beam, it emits several signals (back-scattered and secondary electrons, electromagnetic rays: X-rays, ir, uv, ...). Qualitative electron-probe microanalysis is based on the measurement of some radiation X. The X radiation intensity depends on the initial energy of the incident beam, on the element concentration which corresponds to the radiation, and, on the direction of the incident beam with regard to the plane surface of the target. Few programs study the effect resulting from varying the beam incidence angle. It is important to know to what extent parameters of microanalysis are effected by changes in the beam incidence angle. In this paper, we attempt to study the mean depth reached by incident electrons in a semi-infinite target. In fact, the absorption factor increases when the incidence angle decreases: this is because characteristic X-rays are generated closer to the target surface.     

Transmitted scattered light from a thin film with shallow random rough interfaces

The transmitted scattered energy of plane electromagnetic waves from a thin metallic film with shallow rough interfaces bounded by two semi-infinite media is calculated. Both interfaces are modeled as independent stationary random processes with a Gaussian roughness spectrum. Scattering of light is calculated for both TM (p) or TE (s) polarizations for normal and oblique angles of incidence. An integral equation is obtained for the transmitted field based on the Rayleigh method and their solution involves Fourier coefficients, depending on the roughness profiles. We present some results for the case of a single thin metallic film in the attenuated total reflection configuration for s and p polarization around the angle of the excitation of surface-plasma waves θ(sp). The transmitted scattered intensity shows a maximum at the resonant angle θ(sp) in the case of p polarization.     

CO2两相喷嘴延迟膨胀过程机制研究

本文针对CO2引射器主动流喷嘴渐扩段3个角度0. 076°、0. 306°、0. 612°,对比了均相平衡模型、延迟平衡型、延迟平衡耦合摩擦模型的模拟结果,并与文献实验数据作对比,探讨了非平衡相变和壁面摩擦两种流动机制对相应角度下喷嘴延迟膨胀过程的主导作用。结果表明:在本研究范围内,渐扩段角度较大(θ3=0. 612°)时,均相平衡模型预测的压力分布与实验结果吻合较好;渐扩段角度处于中间值(θ2=0. 306°)时,非平衡相变成为主导机制,延迟平衡模型模拟的压力分布平均误差为11. 87%;渐扩段角度较小(θ1=0. 076°)时,壁面摩擦是导致喷嘴延迟膨胀的主要机制,延迟平衡模型耦合摩擦模型预测的压力分布平均误差为15. 10%,延迟平衡耦合摩擦模型后发现喷嘴真实喉部后移至渐扩段,延迟平衡模型预测的质量流量较均相平衡模型仅减小0. 029%~0. 270%;渐扩段角度较小(θ1=0. 076°)时,延迟平衡模型耦合摩擦模型预测的质量流量相比于均相平衡模型明显减小了9. 95%;当喷嘴渐扩角为0. 306°和0. 612°时,相比于均相平衡模型结果,延迟平衡模型耦合摩擦模型预测的质量流量分别减小了0. 31%和0. 088%。     

Colors of transparent submicron suspensions on approaching the Rayleigh regime

The features of scattered and transmitted light by dilute suspensions of transparent submicron particles are investigated both in the spectral and in the perceived colorimetric domains, as a function of effective particle diameter D, particle-host refractive-index mismatch m, and scattering angle θ. Our results show that the wavelength λ-dependence of the scattering and extinction cross sections remains quite similar well beyond the Rayleigh regime up to particle sizes of a few hundreds nm, but only for specific scattering angles that depend on D and m, and tend to 90° on approaching the Rayleigh regime. Close to this limit (D/λ<1), a simple criterion that relates the perceived scattering color at θ=90° and the ratio of the sample extinction coefficients at two properly selected wavelengths is demonstrated. A comparison between computed and measured data is presented.     

Diffraction of horizontally polarized ultrasonic plane waves on a periodically corrugated solid-liquid interface for normal incidence and Brewster angle incidence

The theory, and the use at normal incidence, of shear-vertically polarized waves (with polarization vector in the plane containing the incident wave vector and the normal on the interface) using the mode conversion method has been tackled by others. Here we develop the theory for shear-horizontally polarized incident waves (with polarization vector perpendicular to both the normal on the interface and the incoming wave vector). We take into account normal incidence as well as oblique incidence. For normal incidence, we discover the generation of Love waves. If oblique incidence is considered, we discover the existence of a Brewster angle of incidence, comparable with the Brewster angle in optics, in which a diffraction grating can be used as a polarization filter.     

Effect of angular response properties of personal dosemeters on the estimation of effective dose using two dosemeters

Even though the two-dosemeter approach successfully solved the underestimation problem of the single-dosemeter approach for posterior incident radiations, this approach significantly overestimates effective dose for the lateral and overhead beam directions when isotropic-responding dosemeters are used for measurement. This kind of overestimation can be reduced by using anisotropic-responding dosemeters whose responses decrease as the incident angle increases, i.e. from 0 degree (normal incidence) to 90 degrees (lateral incidence). To quantify the reduction of overestimation by using anisotropic-responding dosemeters, this study applied the two-dosemeter approach to several types of anisotropic-responding dosemeters--both ideal and commercial--and then compared the results with those of isotropic-responding dosemeters. This study also derived a set of angular response factors (ARF) which can be used to develop a personal dosemeter with ideal angular response properties for use in the two-dosemeter approach.     

Angle-multiplexed holographic data storage with minimum cross talk noise

The cross talk noise-to-signal ratio (NSR) of an angle-multiplexed holographic data storage system is studied, and we propose a method to determine the optimized multiplexing spacing with which the cross talk noise can be less than the conventional method. In our method, the optimization location at the image plane can be chosen arbitrarily, so the multiplexing of asymmetrical image patterns can be optimized. In particular, we investigate the 90° scheme and the transmission scheme angle multiplexing. For the 90° scheme, a holographic medium with a higher refractive index is recommended for cross talk-limited multiplexing. For the transmission scheme, a holographic medium with a lower refractive index is recommended for angular range-limited multiplexing. In addition, for the transmission scheme, a larger angle between the object arm and the reference arm results in less cross talk noise, whereas the highest storage density is achieved at a 45° angle.