Concept of a miniature optical spectrometer using integrated optical and micro-optical components

We describe the concept of a super compact diffractive imaging spectrometer, with optical components a few millimeters across in all dimensions, capable of detecting optical fluorescence spectra within the entire visible spectral range from 400 nm to 700 nm with resolution of the order of 2 nm. In addition, the proposed spectrometer is capable of working simultaneously with multiple, up to 35, independent input optical channels. A specially designed diffractive optical element integrated with a planar optical waveguide is the key component of the proposed device. In the preliminary experimental tests, a uniform waveguide grating with a microlens was used to mimic operation of the diffractive optical element. A microspectrometer with optical components measured below 1 cm in all dimensions covers the spectral range from 450 nm to 650 nm and shows a spectral resolution of 0.5 nm at wavelengths close to 514 nm and 633 nm.     

Surface characterization of Ag-ITO cermet films prepared by a new sol-gel method

Incorporation of Ag nanocrystal into indium tin oxide films (Ag-ITO) could enhance the conductivity of transparent oxide thus attracts more and more interest. Ag-ITO films were prepared by a modified sol-gel method. The surface structure was investigated by X-ray diffraction, X-ray diffuse scattering, and X-ray photoelectron spectroscope techniques. The results showed that stannous chloride worked well as the reduction agent of silver and ion donor source, resulting in high quality nanocomposite thin films. The embedment of silver nanoparticles decreased the crystallization temperature and inhibited the growth of indium oxide. Ag-ITO films have a hierarchical structure. Furthermore, the nanocomposite films were densified and homogenized through prolonging the thermal duration time. XPS results confirmed that a small amount of silver oxide appeared.     

Surface cracks in fatigued structural components: a review

Surface cracks are a common occurrence in structural components due to the frequently highest values of the stress at the outer boundary of the body and to the presence of defects. Such flaws can heavily reduce the service life of structural components leading to their premature failure, especially under repeated loading. During last decades, many research works based on theoretical, numerical and experimental techniques have been performed, mainly devoted to the determination of the stress‐intensity factors for recurrent surface crack shapes, different loading types and boundary conditions. Further, fatigue behaviour of surface cracks has been examined through numerical analyses or by simplifying the expected crack growth process. In the present paper, a literature survey is carried out by discussing the main topics related to the safety assessment of structural components with surface cracks under static or fatigue loading.     

A GA-based method to reduce material handling: the case of TFT-LCD array Fabs in Taiwan

This study proposes a genetic algorithm (GA)-based Material Handling Strategy Function (MHSF) method to increase the productivity of a TFT-LCD array fabrication to improve the traditional FIFO method in TFT-LCD fabrication by the reduction of the material handling for a Rail Guided Vehicle (RGV), because costs of material handling count up to about 50% of production costs. In this article, the MHSF is provided to help material handling commands choice, where a novel GA approach is used to adapt the weights of affecting factors in the function. Finally, to evaluate the performance of the proposed method, experiments using the data from a major TFT-LCD manufacturing plant in Taiwan have been carried out, and the results indicate that it can indeed reduce fabrication time and increase productivity.     

Vibrating knife-edge technique for measuring the focal length of a microlens

A vibrating knife-edge technique is proposed for measuring the focal length of a microlens. The technique is based on the propagation properties of Gaussian beams. A laser beam with a Gaussian intensity profile is focused in front of the microlens under test. After being transmitted through the microlens, the beam propagates toward a detector, which consists of a photodiode that is half blocked by a knife-edge. The photodiode integrates approximately half the intensity of the transmitted beam. The knife-edge vibrates sinusoidally with small amplitude in a plane normal to the direction of propagation. Our analysis shows that the output signal at the photodiode consists of a dc component plus a temporal sinusoidal signal whose amplitude is proportional to the focal length of the microlens. After system calibration, the focal length is measured with an envelope detector or a lock-in amplifier.     

Beam quality characterization of a radial laser array

Abstract

With the Hermite-Gaussian mode used to describe radial laser arrays and the M²-factor and power in the bucket (PIB) chosen as criteria for characterizing beam quality, a detailed study of beam quality of coherent and incoherent radial laser arrays is made. The closed-form expression for the M²-factor of incoherent radial arrays, which depends upon the Hermite-Gaussian order m, inverse radial fill factor r' and aspect ratio w _0x /w _0y , is derived. Numerical examples are given to illustrate and compare beam quality of coherent and incoherent radial arrays.     

Surface characterization techniques for determining the root-mean-square roughness and power spectral densities of optical components

Surface topography and light scattering were measured on 15 samples ranging from those having smooth surfaces to others with ground surfaces. The measurement techniques included an atomic force microscope, mechanical and optical profilers, confocal laser scanning microscope, angle-resolved scattering, and total scattering. The samples included polished and ground fused silica, silicon carbide, sapphire, electroplated gold, and diamond-turned brass. The measurement instruments and techniques had different surface spatial wavelength band limits, so the measured roughnesses were not directly comparable. Two-dimensional power spectral density (PSD) functions were calculated from the digitized measurement data, and we obtained rms roughnesses by integrating areas under the PSD curves between fixed upper and lower band limits. In this way, roughnesses measured with different instruments and techniques could be directly compared. Although smaller differences between measurement techniques remained in the calculated roughnesses, these could be explained mostly by surface topographical features such as isolated particles that affected the instruments in different ways.     

Fabrication of a high-precision spherical micromirror by bending a silicon plate with a metal pad

We demonstrate here the fabrication of a smooth mirror surface by bending a thin silicon plate. A spherical surface is achieved by the bending moment generated in the circumference of the micromirror. Both convex and concave spherical micromirrors are realized through the anodic bonding of silicon and Pyrex glass. Since the mirror surface is originated from the polished silicon surface and no additional etching is introduced for manufacturing, the surface roughness is thus limited to the polishing error. This novel approach opens possibilities for fabricating a smooth surface for micromirror and microlens applications.     

Surface alloying of miniature components by micro-electrical discharge process

Surface alloying is necessary to enhance the surface features of machine elements. In the present study, feasibility of micro-electric discharge machining (micro-EDM) process for surface alloying has been investigated. Experiments are conducted on Nickel sheets using tool of Ti6Al4V with EDM oil and kerosene as dielectric. The surface modification takes place by spark discharges on localized regions of the work piece and the tool surface causing melting of tool and work piece, disassociation of dielectric, alloying, and quenching in the electrolyte. The samples were analyzed by field emission scanning electron microscope equipped with energy-dispersive X-ray spectroscopy, microhardness testing machine, and X-ray diffraction. Recast layers obtained have distinct structure and composition as compared to the work piece. Average recast layer thickness varied from 10.72 to 69.8?µm in case of EDM oil and from 13.5 to 31.6?µm in case of kerosene by varying voltage, pulse duration (on time) and frequency during the experiment. The microhardness of the machined surfaces was obtained in a wide range of 161.61–338.25 HV whereas the microhardness of unaffected base metal was 132.25 HV. Titanium carbide (TiC) was deposited and consequently there was improvement in the hardness of the work piece.     

Surface free energy components of silica gel determined by the thin layer wicking method for different layer thicknesses of gel

The influence of the thickness of silica gel layer on the penetration rate of selected liquids and, in consequence, on the value of surface free energy components determined by thin layer wicking method was studied. Plates of the following gel thickness were used: 0.25, 0.5, 1.0 and 2.0 mm. Measurements of the penetration rate of apolar liquids, i.e. three alkanes: octane, nonane and decane, diiodomethane, -bromonaphthalene and two polar liquids: water and formamide were made for this purpose. From the obtained relationships x2=f(t) the suitability of Washburns equation in the whole penetration range (9 cm) was confirmed for all thicknesses of porous layers. However, the penetration rate of probe liquids changed with the thickness of the deposited layer, it was mainly dependent on an effective (apparent) radius of the interparticle pores. Using these results and the appropriate form of Washburns equation surface free energy components of silica gel 60 (for four thicknesses of layer) were calculated. It was found that values of apolar Lifshitz–van der Waals (LWs=41.7±0.9 mJ m-2) and polar acid–base (ABs=11.5±0.5 mJ m-2): electron donor (-s=50.8±0.9 mJ m-2) and electron acceptor (+s0.7±0.1 mJ m-2) components of surface free energy were very similar for different layer thicknesses. Even in the case of a 2 mm thick layer reproducible values of both Lifshitz–van der Waals and acid–base component were obtained. It is important when the thin layers are prepared in laboratory conditions, i.e. from suspensions by water evaporating, and the deposited layer is of less controlled thickness. When diiodomethane and -bromonaphthalene are considered as weakly polar liquids, the value of Lifshitz–van der Waals component of silica gel is very close to LWs determined from n-alkanes.     

The inspection of anisotropic single-crystal components using a 2-D ultrasonic array

Single-crystal metal alloys are used extensively in the manufacture of jet engine components for their excellent mechanical properties at elevated temperatures. The inspection of these components using 2-D ultrasonic arrays potentially allows the detection of subsurface defects in threedimensions from one inspection location. Such methods are not currently suitable for the inspection of single-crystal components because the high elastic anisotropy of single-crystal materials causes directional variation in ultrasonic waves. In this paper, a model of wave propagation in anisotropic material is used to correct an ultrasonic imaging algorithm and is applied to a single-crystal test specimen. For this correctedalgorithm, the orientation of the crystal in a specimen must be known before the inspection. Using the same ultrasonic array to measure the orientation and perform the defect inspection offers the most practical solution. Therefore, potential crystallographic orientation methods using 2-D ultrasonic arrays are also developed and evaluated.     

Synthesis and characterization of fluorine-containing hydroxyapatite by a pH-cycling method

Different fluorine-containing hydroxyapatite (FHA) powders were synthesized through a pH-cycling method by varying sodium fluoride (NaF) concentration in hydroxyapatite (HA) suspensions. The powders were then calcined at 1200 C for 1 h. Both uncalcined and calcined powders were characterized using X-ray diffraction (XRD), Fourier transform infra-red (FTIR), and F-electrode. It was discovered that fluorine incorporation increased with the fluorine content in the initial solution and the number of pH cycles employed. A relatively low fluorine incorporation efficiency, 60%, was attained for most of the FHA samples, and it did not vary significantly after calcination. It was also revealed that the FHA particles produced by the pH-cycling method were inhomogeneous. They were a mixture of hydroxyapatite and F-rich apatite (or FA) particles. After calcination, however, these FHA particles were homogenized and became single phased FHA.     

Structural characterization of silicon-substituted hydroxyapatite synthesized by a hydrothermal method

Silicon-substituted hydroxyapatite (Si-HA) was prepared successfully by hydrothermal method. The crystalline phase, microstructure, chemical composition, morphology and thermal stability of Si-HA were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results show that the substitution of the silicate groups for the phosphate groups causes some OH^- loss to maintain the charge balance and changes the lattice parameters of HA. Furthermore, the substitution of the silicate groups restrains the growth of Si-HA crystal. DSC analysis shows that the small amount of silicon incorporates into HA lattice does not influence the thermal stability of HA.     

Synthesis of CoPt nanoparticles by a modified polyol method: characterization and magnetic properties

CoPt nanoparticles with an average size of 3?nm and narrow distribution were synthesized by chemical reduction of Co(CH(3)COO)(2) and Pt(acac)(2) by polyethyleneglycol-200. The as-prepared nanoparticles have a disordered fcc structure which transformed after thermal treatment to an ordered fct structure, which results in coercivity up to 6?kOe at room temperature and 9?kOe at 5?K because of the high magnetocrystalline anisotropy of the tetragonal structure [Formula: see text].     

Mechanical behaviour of a two-phase material from the behaviour of its components: Interface modelling by finite element method

In this paper, the principle of a solution for “thermal” connection between two solids is analyzed. We shows results given by the solution applied to the mechanical behaviour of a γ/γ′ two-phase material and to “artificial” structures obtained from modern techniques for epitaxial deposit. It appears that the use of a true or fictitious thermal loading constitutes a simple “connection” procedure, but is particularly coherent with the mechanics of two-phase crystalline materials with different lattice parameters. It would be interesting to apply the model to real structures, with misfit and interfacial dislocations.     

A novel method for reducing the dimensionality in a sensor array

Specific types of gas sensors are normally produced by adding different dopants to a common substrate. The advancement of technology has made the fabrication of many dopants and consequently various sensors possible. As a result, in each family of gas sensors, one can find tens of different sensors which are only slightly different in the spectrum of response to various volatile compounds. The wide variety of available gas sensors creates a selection problem for any specific application. Sensor selection/reduction becomes even more important when cost and technology limitations are issues of concern. Accordingly, a methodology by which one can tailor a sensor array to a specific need is highly desirable. In this paper, a novel method is introduced to address this task using data from an electronic nose that uses polymer gas sensors. This method has been delineated based on the geometry of eigenvectors in Karhunen-Loeve expansion. The methodology is general and therefore suitable for many other feature selection problems     

Annealing effect on the photoluminescence properties of ZnO nanorod array prepared by a PLD-assistant wet chemical method

Well-aligned ZnO nanorod arrays were synthesized by a wet chemical method on the glass substrate with ZnO thin film as seed layer prepared by pulsed laser deposition. The effect of annealing temperature on the luminescence characteristics was investigated. As the annealing temperature increased, the photoluminescence properties show a general enhancing tendency. The nanorod array with high ultraviolet emission and negligible visible light emission (designated by the photoluminescence intensity ratio of ultraviolet to visible emission of 66.4) is obtained by annealing the sample at 700 °C for 1 h. Based on the results of X-ray photoelectron spectroscopy and photoluminescence spectra, the mechanisms of visible emission were discussed.