Random thickness errors-effect on reflectance of multilayer

In this paper the effect of thickness errors on the reflectance of multilayer is investigated. Using the matrix method, we deduced an expression for describing the dependence of reflectance on the film thickness errors. It is found that the degree of the thickness error-effect is affected by the ratio of low refractive index with high refractive index and the number of layer of multilayer. The computer simulations show that the degree of this effect is very small when the ratio is small and the number of layer is large. The thickness error hardly influences the reflectance of short-wave multilayer.     

Near-Field Birefringence Response of Liquid Crystal Molecules in Thickness Direction of Liquid Crystal Thin Film Orientated by Shear Force

Information of molecular orientation in nematic liquid crystal （LC） is attractive and important for applications in the field of display devices. We demonstrate a novel method using a birefringence scanning near-field optical microscope （Bi-SNOM） with a probe which is inserted into the LC thin film to detect the molecular orientation from its birefringence responses in the thickness direction of the LC thin film. The probe is laterally vibrated when going forward into the LC thin film, and the retardation and azimuth angle are recorded as the probe going down. Firstly, the thickness of the LC thin film is measured by the shear force detection. Since the shear force acts as a stimulation to reorientate the LC molecules above the substrate surface, we can detect the molecular orientation caused by a polyimide alignment substrate and the effect to molecular orientation caused by vibration of fibre probe. As a result, the orientation profiling of the LC film in depth direction is obtained in both the cases that the direction of probe vibrating is vertical/parallel to the rubbing direction of the alignment film. Furthermore, the thickness of completely orientated layers just above the substrate surface can also be obtained by either vibrating probe or no-vibrating probe. Ultimately, the LC thin film can be modelled in thickness direction from all the results using this method.     

Large Positive and Negative Lateral Displacements from Total Internal Reflection Configuration with a Weakly Absorbing Dielectric Film

It is theoretically shown that the simultaneously large positive and negative lateral displacements will appear when the resonant condition is satisfied for a TE-polarized light beam reflected from the total internal reflection configuration with a weakly absorbing dielectric film. Appearance of the enhanced negative lateral displacement is relative to the incidence angle, absorption of the thin film and its thickness. If we select an appropriate weakly absorbing dielectric film and its thickness, the simultaneously enhanced positive and negative lateral displacements will appear at different resonant angles. These phenomena may lead to convenient measurements and interesting applications in optical devices.     

In situ etch rate measurements of thin film combinatorial libraries

We demonstrate the use of optical reflection mapping as an in situ characterization tool to evaluate the corrosion rate of compositionally graded thin film combinatorial libraries coated with a commercial glass etching paste. A multi-channel fiber-optically coupled CCD-array-based spectrometer was used to collect a series of reflectance maps from 300 to 1000 nm versus time. The thin film interference oscillations in the measured reflection spectra have been fitted to determine the film thickness as a function of time and thereby the etch rate. Application of this technique to an In-Mo-O composition spread library is presented as an example.     

超二代微光像增强器多碱光电阴极膜厚测量研究

介绍了多碱光电阴极的光学性能和光谱反射率特性,测量了多碱阴极的光谱反射率曲线.该曲线与普通光学膜层光谱反射率曲线相比,形状较不规则,原因是多碱阴极膜层存在光吸收.光谱反射率曲线上的干涉峰是入射光在玻璃与阴极膜层界面反射和在阴极膜层与真空的界面反射的两束光发生干涉的结果.根据干涉的原理,如果阴极膜层所反射的两束光的光程差为二分之一波长的偶倍数时,光谱反射将出现干涉加强峰;如果阴极膜层所反射的两束光的光程差为二分之一波长的奇倍数时,光谱反射将出现干涉减弱峰.根据超二代像增强器光谱反射干涉峰对应的波长,可以计算出其阴极膜层的厚度约为191 nm,比二代像增强器阴极膜层的厚度增加了38％.多碱阴极膜层厚度是影响多碱阴极灵敏度的一个关键参量,仅仅靠人眼观察阴极膜层颜色的方法不准确.实践证明,利用光谱反射的方法来计算阴极膜层厚度的方法简单有效.如果在多碱阴极的制作过程中进行光谱反射率的监控,那么将可以精确控制阴极膜层的厚度,对多碱阴极的研究将会更加深入,多碱阴极的灵敏度也将会得到进一步的提升.     

Independent Modulation of Omnidirectional Defect Modes in Single-Negative Materials Photonic Crystal with Multiple Defects

Single-negative materials based on photonic crystal with multiple defect layers are designed and the free modulation of defect modes is studied. The results show that the multi-defect structure can avoid the interference between the defect states. Therefore, the designed double defect modes in the zero effective-phase gap can be adjusted independently by changing the thickness of different defect layers. In addition, the two tunable defect modes have the omnidirectional characteristics. This multi-defect structure with above-mentioned two advantages has potential applications in modern optical devices such as tunable omnidirectional filters.     

Large forbidden band in one-dimensional multi-layered structure containing exponentially graded materials

In the present communication, we have presented band spectra and reflectance properties of one-dimensional multi-layered structure containing dielectric exponentially graded and simple dielectric layers. This study has been performed theoretically by using transfer matrix method. In this paper we have taken the multi-layered structure where refractive index of odd layers is varying continuously along the direction perpendicular to the surface of the layer in exponential form. The effect of the graded profiles are studied and compared with the conventional multi-layered structure of suitable contrast of refractive indices in detail. In this study the materials are considered as non-magnetic and layers other than the graded are taken to be homogeneous and isotropic dielectric medium of constant refractive index. It has been found that the introduction of graded layers enhanced the forbidden band gaps and affects the reflectance of electromagnetic wave spectra significantly. By changing the grading profiles and the contrast, we obtained the forbidden band gaps and the reflectance of such structural change accordingly. Therefore, introducing a graded exponential layer of dielectric in the one-dimensional multi-layered structure provides possible mechanism for enhancing the reflectance as well as the forbidden gap in the optical region. Such multi-layered structure may be useful in the design of a broadband filter.     

Quarter-wavelength multilayer interference filter for terahertz waves

This work presents a multilayer interference filter, suitable for operation with terahertz waves (T-rays). An analysis of the effect of the number of layers on the spectral response is given, with full measurement data including time-resolved signals, transmittances, and phase spectra. The silicon-air structure with a submillimeter thickness shows a stop-band between 0.2 and 0.5 THz, and the attenuation inside the stop-band increases in proportion to the number of layers in the structure. The measurement of the fabricated structure is in agreement with a characteristic matrix analysis.     

Temperature profile of the multilayer structure irradiated by pulsed laser

Two programs are developed to calculate the temperature profile, as well as the reflectance, transmittance and absorption of a given multilayer film structure, in order to better understand the laser energy distribution between the reflectance, transmittance and absorption in each film layer. An inorganic Blu-ray recordable disc (BD-R) structure is used as a practical demonstration of the multilayer structure. The reflectance and absorption of the BD-R structure exhibit opposite trends and oscillate repeatedly with varying lower or upper dielectric layer thickness while the rest of the film thickness remains unchanged. The energy absorption in an absorbed layer depends on the thickness of the dielectric layers, its relative position in the structure and the extinction coefficient of its optical constant. The total absorption ratio of its maximum to minimum can be over 3 when changing the lower dielectric layer thickness of the studied structure. The layer thickness acts as an energy valve to control the energy flow into the multilayer structure. The thermal profile of the multilayer film structure irradiated by a pulsed laser is calculated at different positions in the film layers with time. The calculated temperatures in the recording alloy layer exhibit linear relationship with the applied power level. The effect of the laser duration time on the temperature increase in the recording layer is significant in the first few nanoseconds and becomes saturated if the heat balance is established in the structure. The calculated temperature is consistent with the experimental recording result when the structure is recorded at 4-time BD-R recording speed.     

SNOM Observations of Surface Plasmon Polaritons on Metal Heterostructures

We observe surface plasmon polariton （SPP） refraction on a metal heterostructured sample with a scattered-type scanning near-field optical microscope （SNOM）. The sample consists of AI and Au in-plane whose boundary is smooth enough with proper etching time. SPPs excited on the AI film travel to the boundary and a portion of SPPs propagates into the Au film. In addition, interference fringes appear in the SNOM image bent at the boundary. The result is analysed with effective index method and the refracted angle is explained by Shell＇s law.     

Photonic nanojet modulation by elliptical microcylinders

The detailed analysis of localized photonic nanojets generated at the shadow side surfaces of dielectric elliptical microcylinder illuminated by a plane wave is reported. We have studied the distribution of the electric energy density within and in the vicinity outside an elliptical microcylinder by using finite-difference time-domain calculation with high resolution. The location of photonic nanojet depends on the radius ratio of the microcylinder. We have further analyzed the effect of the rotation angle of elliptical microcylinder upon the focal length of photonic nanojets. The horizontal and vertical shifts of photonic nanojet can be changed by rotating the rotation angle of elliptical microcylinder. The mechanisms of elliptical microcylinder may supply a new ultra-lens approach to distinguish nanoscale targets such as nanoparticles, optical gratings, and nanoscale surface roughness.     

Thickness Dependence of Resistivity and Optical Reflectance of ITO Films

Indium-tin-oxide （ITO） films deposited on crystalline silicon wafer and Corning glass are prepared by directcurrent magnetron sputtering method at room temperature with various thicknesses. The thickness dependences of structure, resistance and optical refectance of ITO films are characterized. The results show that when the film thickness is less than 40 nm, the resistivity and optical reflectance of the ITO film changes remarkably with thickness. The optoelectrical properties trend to stabilize when the thickness is over 55 nm. The GXRD result implies that the ITO film begins to crystallize if only the thickness is large enough.     

Untersuchung der Lichtstreuung von transparenten Einfachschichten auf Glassubstraten

Investigations of Light Scattering from Transparent Single Layers on Glass Substrates In the present paper the influence of stochastic interface roughness as well as film thickness on light scattering from dielectric single layers is investigated. By calculations carried out on base of Elson's vector scattering theory especially the importance of correlation functions of microroughness is analyzed. Measurements made from sputtered TiO₂-films show dominating interface scattering and an interference phenomenon, depending on film thickness.     

Giant positive and negative lateral shifts from the Kretschmann-Raether configuration with a weakly absorbing left-handed slab

The lateral shift of a TE-polarized beam reflected from the Kretschmann-Raether structure with a weakly absorbing left-handed slab is studied theoretically. It is shown that the lateral shift can be very large negative as well as positive near the resonant condition. These large negative and positive shifts can be one order of magnitude much larger than the shift from the corresponding nonabsorbing slab. As the absorption factor increases, the incident angle of producing largest lateral shift increases when the thickness is kept unchanged but the thickness of the slab of producing largest lateral shift decreases when the incident angle is kept unchanged.     

Method of envelopes for studying a two-film system on a reflecting substrate

For determining the optical constants and the thickness of thin films (including strongly absorbing films) by the spectrophotometric method, we propose to deposit them on intermediate films formed on strongly reflecting substrates. Due to this, an interference pattern depending on the optical constants and the thickness of the film under study will be observed in the reflectance spectrum. The method of envelopes of the extrema in the reflectance spectrum that is based on the iterative approach is developed for studying two-film systems.     

Optical parameters of epitaxial GaN thin film on Si substrate from the reflection spectrum

A method has been proposed for determining the optical properties of a thin film layer on absorbing substrates. The film optical parameters such as thickness, refractive index, absorption coefficient, extinction coefficient and the optical energy gap of an absorbing film are retrieved from the interference fringes of the reflection spectrum at normal incidence. The envelopes of the maxima of the spectrum E_M and of the minima E_m are introduced in analytical forms to find the reflectance amplitudes at the interfaces and approximate values of the thin film refractive index. Then, the interference orders and film thickness are calculated to get accurate values of the needed optical parameters. There are no complex fitting procedures or assumed theoretical refractive index dispersion relations. The method is applied to calculate the optical properties of an epitaxial gallium nitride thin film on a silicon (1 1 1) substrate. Good agreement between our results and the published data are obtained.     

Broadband dielectric film transflector for variable transmission optical filters

A broadband multilayer dielectric film transflector for applications in variable transmission optical filters is proposed. The dielectric film is composed of alternating TiO₂ and SiO₂ layers deposited on a substrate. The transmittance of the dielectric film transflector can be varied from 0 to 100% by adjusting the individual dielectric layer thickness and the number of layers. The conjugate gradient method is used to optimize the design of the transflectors. The obtained transflectors have good transmittance and reflectance within the whole visible range and the incident angle range 0-20°. The manufacturing tolerances on film thickness and refractive index are reasonably large.     

Enhancing the Resistance of Spectral Characteristics of Interference Coatings to Deviation in Parameters of Layers Entering into Their Composition

A new method of enhancing the resistance of spectral characteristics of interference coatings to deviations in parameters of layers entering into their composition is presented. The spectral characteristic that can be obtained using this method for the energy transmittance (or reflectance) of an experimentally manufactured coating is maximally close to the characteristic of the synthesized coating. A way to use several samples for monitoring the thickness of layers during the process of their formation with the aim to reduce the deviation of optical layers during manufacturing of interference coatings is presented.

     

多种薄油膜光谱反射率特性外场测试方法及结果分析

水面溢油机载航测工作需要以全面的溢油模拟目标的光谱反射率特性数据作为支撑,选择合适的工作波段,并通过获得的数据对溢油情况进行分析与判断。针对汽油、柴油、润滑油、煤油与原油五种目标样本,油膜从紫外波段到近红外波段进行了反射光谱测量,并将结果与相同实验环境下的水的反射光谱对比。实验结果表明油膜的光谱反射特性与油品类型以及油膜的厚度相关。不同种类的油膜在相同厚度的情况下,光谱反射率曲线的差异很大,而同一种类的油膜,随着油膜厚度的改变,光谱反射率曲线亦随之发生改变,因而就单一油膜而论,可以通过反射率曲线区分不同的油膜厚度。以相同的油膜厚度而论,柴油,煤油,润滑油在380 nm附近存在反射率峰值,与水的反射率差异明显,原油在大于340 nm波长的反射率远小于水,所得到的反射光谱能够在一定程度上区分不同类型油膜。实验涉及主要溢油油种,数据全面覆盖探测常用的光谱波段,定量化描述了油膜光谱反射率特性,为机载水面溢油探测工作的波段选择与水面溢油的早期发现与分析提供了全面的理论与数据支持。     

Prevailing effects of interference or diffraction by multiple apertures

The effects of interference and diffraction produced by a bidimensional structure composed of multiple and identical apertures are studied. Such effects are competitive during the propagation, that is, in some planes the interference effects are more visible, while in others prevail the diffraction ones. Using the number of Fresnel zones, the spatial domains where the interference or diffraction effects prevail are defined and parameterized. Simulation and experimental results are further introduced to verify the proposed method.