Mode-locked laser cavities with a single prism for dispersion compensation

We demonstrate the use of a single prism for adjustable dispersion compensation in a mode-locked laser cavity, instead of the standard approach with a prism pair. A simple model based on the prism-pair configuration is presented to determine the group-velocity dispersion by use of ray optics to trace the wavelength-dependent optical axes through the cavity. We experimentally demonstrated this concept with a passively mode-locked diode-pumped Nd:glass laser producing 200-fs pulses with a 200-mW average output power, using only one intracavity prism. The advantages of such a cavity design are simple alignment, reduced loss, and lossless wavelength tunability This technique can be generalized to other angularly dispersive elements such as prismatic output couplers.     

Scanning delay line with a rotating-parallelogram prism for low-coherence interferometry

We describe a fast scanning optical delay line for low-coherence interferometry that has good linearity, a high duty cycle, and a continuously adjustable scan range. The delay line consists of a rotating-parallelogram prism with the rotation axis tilted with respect to the incident beam and two motionless mirrors. The delay line is well suited for nearly simultaneous distance measurements at two different depths, which is useful for making absolute and differential distance measurements.     

NOmarski棱镜的优化设计

Nomarski棱镜广泛应用于微计量检测系统,其应用特点在于将一束偏振光分解为两束振动方向彼此垂直的偏振光,从而形成干涉成像.在构成的微分干涉相衬显微镜系统中,系统相干面的位置可以通过Nomarski棱镜的结构参数来决定.本文根据相干平面与系统物镜焦面重合的准则,建立了棱镜各参数间的关系模型.在分析Nomarski棱镜各参数关系基础上,利用计算机模拟了棱镜各参数的优化设计,绘制了相应参数间的关系曲线,为棱镜的设计提供了理论依据.     

聚碳酸酯在汽车和航空透明材料领域应用的研究进展

概述了聚碳酸酯在汽车及航天透明材料领域的应用性能优势,介绍了聚碳酸酯材料在汽车和航空透明材料领域中的应用研究进展.聚碳酸酯作为优良的工程塑料,具有传统无机玻璃不可比拟的众多优势,因而在汽车和航空材料领域的应用将日趋广泛,并将随着聚碳酸酯合成及应用技术的发展逐渐占据主导地位.     

Influence of reprocessing on properties of polycarbonate

The influence of reprocessing by injection moulding on properties of polycarbonate has been studied. It was found that reprocessing does not affect the tensile strength, flexural strength and flexural modulus of the polycarbonate material. Fracture parameters such as fracture toughness and the material resistance to crack propagation, also showed no variation with the number of reprocessing cycles, although both were strongly dependent on sample width. Dynamic mechanical analysis (DMA) also indicated that reprocessing has no significant effect upon dynamic mechanical properties of polycarbonate. Results further indicated that the glass transition temperature of polycarbonate is not affected by reprocessing, only the range over which it occurs seems to be broadened by reprocessing due to increase in molecular weight with number of reprocessing cycles.     

Finite prism analysis of plates and shells

The finite prism technique introduced by Zienkiewicz and Too⁴ is extended to include 12-node prism elements and, more importantly, a novel offset beam element. The use of 12-node prism elements enables parabolic strain distributions to be simulated, this being useful for structures which have strongly tapered cross-sections. The offset beam element is used to simulate flexure and torsion of a beam whose centroid is offset from the main structure. The element is specified completely at the nodes of adjacent prism elements and so is not really an ‘element’ in the usual sense. The analysis is applied to thin and thick plates and to shells, with and without edge beams. It is shown to be more versatile than the finite strip method and it requires smaller computer resources than the finite element method. Experimental verification of the analysis is obtained by comparison with measurements for a double-T bridge deck tested by Loo¹⁴.     

Trichroic prism assembly for separating and recombining colors in a compact projection display

A trichroic prism assembly design, believed to be new, is proposed and demonstrated. This new design has the advantages of low s- and p-polarization dependence in the reflectance spectra of the optical coatings. Hence it can be used for both color separation and color recombination with polarization change. This new trichroic prism assembly is especially useful in a compact color projector employing reflective liquid-crystal light valves.     

Use of radiation and hybrid modes to increase the accuracy in the determination of the refractive indices of rutile

A new method to correlate prism and substrate refractive indices is presented and applied to the determination of rutile refractive indices, both ordinary and extraordinary, at different wavelengths in the visible and the near infrared. The method exploits radiation modes and, when the sample structure allows it, hybrid modes. An accuracy of approximately 2 x 10(-4) was achieved without the need of any specific preparation of the samples. The method exhibits a good versatility since it can be exploited for the determination of the refractive index of a coupling prism when the substrate index is known and vice versa.     

High-performance nonscanning Fourier-transform spectrometer that uses a Wollaston prism array

A high-performance nonscanning Fourier-transform spectrometer is reported that is composed mainly of a Wollaston prism array and a two-dimensional photodetector array. It is a substantial improvement over existing Wollaston prism based nonscanning Fourier-transform spectrometers because it offers finer spectral resolution and smaller size. Such spectrometers will find important applications in remote chemical and biological sensing, environmental monitoring, medical diagnosis, etc. Experimental results are consistent with theoretical analyses.     

Image inversion and magnification by negative index prisms

A Dove prism and an anamorphic prism pair are investigated in negative index imaging systems. An equilateral triangular prism with refractive index of -1 operates as a negative index Dove prism that inverts as well as images the incident field. A negative index anamorphic prism pair acts as a negative index imaging system with magnification. The relationship between achievable magnification and aberrations is discussed. Both prism systems can be implemented by using negative index photonic crystals, and their performance is demonstrated numerically by the finite-difference time-domain method. These negative index prism structures enhance the functionalities of negative index flat lenses and broaden the applications of negative index materials.     

Heterogeneous nucleation of crazes below notches in glassy polymers

A slip-line field study of craze initiation at plastic zone tips below notches in polycarbonate has been carried out over a wide temperature range. Combination of the critical values of hydrostatic tension with Yee's temperature data for bulk modulus leads to a calculated critical elastic dilation in the region beyond the zone tip that is nearly temperature-independent. Microscopic investigation, however, shows strong evidence that crazes in polycarbonate and other glassy resins initiate at micrometre-size foreign particles. Assuming that the foreign particle is a rigid adherent sphere, a stress analysis for the particle situated on the elastic side of the elastoplastic boundary has been effected; the particle is found to raise the hydrostatic tension over the value in the homogeneous field by 104%. In view of this analysis the polycarbonate experimental results suggest a temperature-independent, critical local elastic dilation of greater than 2% as a crazing criterion. Based on these results it may be suspected that all crazes — surface or internal — in glassy polymers, except at crack tips, are heterogeneously nucleated at impurity sites.     

一种高灵敏度传感器：—四棱镜光点检测器

本文介绍一种用于激光准直高精度直线度测量的高灵敏度光电信号检测器,该检测器根据激光束腰处聚焦光斑点小的特点,采用一种四棱镜光点会聚式检测器来接收激光束信息,它的检测灵敏度比传统的四棱镜式四象限位敏传感器高出一个数量级以上;该检测器对激光束平行漂移与角漂移表现出不同的检出特征,因而尤适合于做为激光束漂移补偿检测和直线度误差检测;该检测器还具有结构简单、使用方便等优点。     

Numerical study on load-bearing capabilities of beam-like lattice structures with three different unit cells

The design and analysis of lattice structures manufactured using additive manufacturing technique is a new approach to create lightweight high-strength components. However, it is difficult for engineers to choose the proper unit cell for a certain function structure and loading case. In this paper, three beam-like lattice structures with triangular prism, square prism and hexagonal prism were designed, manufactured by SLM process using AlSi10Mg and tested. The mechanical performances of lattice structures with equal relative density, equal base area and height, and equal length for all unit cells were conducted by finite element analysis (FEA). It was found that effective Young’s modulus is proportional to relative density, but with different affecting levels. When the lattice structures are designed with the same relative density or the same side lengths, the effective Young’s modulus of lattice structure with triangular prism exhibits the maximum value for both cases. When the lattice structures are designed with the same base areas for all unit cells, the effective Young’s modulus of lattice structures with square prism presents the maximum. FEA results also show that the maximum stress of lattice structures with triangular prisms in each comparison is at the lowest level and the stiffness-to-mass ratio remains at the maximum value, showing the overwhelming advantages in terms of mechanical strength. The excellent agreements between numerical results and experimental tests reveal the validity of FEA methods applied. The results in this work provide an explicit guideline to fabricate beam-like lattice structures with the best tensile and bending capabilities.     

Dove prism with increased throughput for implementation in a rotational-shearing interferometer

An analytical expression is derived for the tilt introduced into a wave front by a Dove prism with manufacturing errors in the prism's base angles and pyramidal angle. We found that the tilt decreases when the base angles are increased above the values of traditional design. The increase in the length-aperture ratio of a prism is detrimental to the prism's performance. However, a Dove prism with a widened aperture increases throughput and maintains a manageable prism weight for implementation in a rotational shearing interferometer. Thus we propose a Dove prism designed with a widened aperture to increase throughput in a rotational shearing interferometer and with larger base angles to minimize the wave-front tilt introduced by manufacturing errors. Experimental results implemented in a rotational shearing interferometer demonstrate the feasibility of this design.     

Design of a high-power Nd:YAG Q-switched laser cavity

An electro-optically Q-switched Nd:YAG laser resonator that uses two end prisms placed orthogonally perpendicular to each other has been designed. This configuration improves the stability of the resonator and does not alter the characteristics of the electro-optical Q switch. The outcoupling ratio of the cavity is optimized by a change in the azimuthal angle of a phase-matched Porro prism placed at one end of the cavity. The prism placed at the other end of the cavity is designed so that it introduces a phase change of II, regardless of its orientation and index of refraction, resulting in a more efficient and stable cavity.     

用Sol-Gel法在PC上制备有机-无机复合耐磨涂层

用ｓｏｌ－ｇｅｌ法在聚碳酸酯ＰＣ上制备一层耐磨涂层。该涂层为有机－无机复合网络,由γ—缩水甘油醚氧丙基三甲氧基硅烷（γ—ＧＰＴＭＳ）和金属醇盐Ｔｉ（ＯＣ２Ｈ５）４合成。采用浸涂工艺,热固化后可得到几微米厚的透明涂层。用３—氨丙基三乙氧基硅烷（３—ＡＰＳ）对ＰＣ表面进行处理,可使涂层与基体的结合力大大提高。涂层的基本骨架由Ｓｉ－Ｏ－Ｔｉ组成,能显著改善ＰＣ材料的耐磨性能。     

Low-loss deflection prism for a laser beam with Brewster angle

A low-loss deflection prism for a laser beam is proposed, and its various characteristics such as beam quality, transmittance, deflection angle, and polarization state are presented. The prism having a trapezoidal form is made from BK7 glass and is designed for a He-Ne laser beam. When a p-polarized beam is incident on the slant surface of the prism at the Brewster angle, the totally reflected and transmitted beam is deflected by 90 degrees, and the measured transmittance is nearly 98%. The theoretical transmittances of the proposed prism are compared with those of a Pellin-Broca prism.     

Determination of second-order derivatives of a skew ray with respect to the variables of its source ray in optical prism systems

The second-order derivative of a scalar function with respect to a variable vector is known as the Hessian matrix. We present a computational scheme based on the principles of differential geometry for determining the Hessian matrix of a skew ray as it travels through a prism system. A comparison of the proposed method and the conventional finite difference (FD) method is made at last. It is shown that the proposed method has a greater inherent accuracy than FD methods based on ray-tracing data. The proposed method not only provides a convenient means of investigating the wavefront shape within complex prism systems, but it also provides a potential basis for determining the higher order derivatives of a ray by further taking higher order differentiations.     

D.c. electrical conduction phenomena between two non-contacting stainless steel fibres in a polycarbonate matrix

Model two-fibre devices have been constructed to simulate the local electrical environment between neighbouring fibres in stainless steel fibre polycarbonate composites. The voltagecurrent characteristics of the device have been studied as a function of the shortest distance (gap length) between the fibres, arranged in T-configurations. From the device behaviour it is concluded that to explain the observed levels of resistivity in bulk composites (as low as a few ohms centimetres for 1% volume fraction of metal) gap levels must be <1 nm. Whilst the device resistance for larger gaps of several micrometres is too large to explain bulk resistivities of a few ohms centimetres in composites, it is nevertheless six orders of magnitude lower than one would expect if tabulated bulk resistivities of polycarbonate (2 × 10⁶ cm) obtained in the gap between fibres. Furthermore the lowest experimental estimate of the dielectric strength of the polycarbonate in the gaps, exceeds by a factor of ten or more the tabulated value for bulk polycarbonate. In the conclusion some tentative suggestions on the origin of these device size effects are presented. This involves consideration of the length and orientation of polymer chains in relation to the gaps and cross-linking effects.     

Impact of biofouling on diffusive gradient in thin film measurements in water

The technique of diffusive gradient in thin film (DGT) is commonly used to assess metal contamination in natural waters. In this paper, we assess the effect of biofouling on DGT measured labile concentrations in water and investigate whether an additional nuclepore polycarbonate membrane on the surface of DGT devices can limit biofilm growth. Simultaneous field deployments of DGT equipped with and without the additional membrane in a canal receiving wastewater were compared. The effect of the biofilm was also assessed in controlled laboratory experiments, completed by the experimental determination of several metals diffusion coefficients in the hydrogel and membrane systems. The biofilms effect was problematic only from the 10th day of accumulation. Accumulation of some elements is highly biased by the presence of a thick biofilm (Zn, Ni, Cd). The polycarbonate membrane improved the quantification of Cd and Ni but adversely affects the quantification of Cr and Co. A kinetic model is proposed to explain the biofilm role on the DGT measurement. Depending on the metals of interest, it is possible to limit bias due to biofilms by using an additional polycarbonate membrane.