Polarization Beam Splitting in Optical Fibre Couplers Due to Form Birefringence

Abstract

Polarization dependent corrections to the scalar coupling coefficients of the fundamental modes on two identical optical fibres are calculated from scalar supermode fields corrected up to first order in weak coupling. The method applies to arbitrary refractive-index profiles.     

Theoretical Modelling of Thulium-sensitized Holmium Continuous-wave Fibre Lasers

Abstract

Theoretical modelling is described which estimates the performance of thulium-sensitized holmium-doped c.w. fluoride fibre lasers at 2020 nm. This model takes into account the mechanisms of cross-relaxation and energy transfer to describe the laser operation. The model uses an iteration technique together with our own measured transition data and shows good agreement with experimental results. This model also provides data for the optimum parameters of the fibre for the configuration of an efficient fibre laser system.     

Influence of Colour Couplers on the Adsorption of Spectral Sensitizing Agents

The spectral sensitivity of a spectrally sensitized emulsion is in many cases altered by the addition of colour couplers. This alteration is mainly due to a partial desorption of the sensitizing agent. Two possible cases of interaction between the colour coupler and the sensitizer hare been studied.

1. The colour coupler itself is not adsorbed on the surface of the silver halide but forms micelles in the gelatin phase. These micelles act as dissolving agents and desorb the sensitizing agent from the surface of the silver halide crystals. The isotherm, giving the amount of sensitizer solubilised by the colour coupler as a function of the amount still adsorbed on the silver halide crystals, has two different saturation levels.

2. The colour coupler is adsorbed In this case the colour coupler and the sensitizing agent scarcely disturb the adsorption of each other A multilayer adsorption is believed to take place     

Spectral Filtering of Light Possessing Non-gaussian Statistics

Abstract

We have used a heterodyne detection technique to observe the intensity fluctuations and statistics of non-Gaussian scattered light, formed by illuminating a rotating ground-glass screen with a tightly focused laser beam. This type of light field contains the characteristic ‘glints’ commonly observed with laser radar systems. It is demonstrated both theoretically and experimentally that the statistics of the fluctuating intensity are significantly altered by spectral filtering of the light. In the limit, when the filter bandwidth becomes much narrower than the overall spectral linewidth of the scattered light, the distribution of intensities tends to that expected for complex Gaussian field statistics (i.e. a negative exponential). We compare this behaviour with that obtained by other workers for spectral filtering within the linewidth of light from a single-mode laser.     

Generation of Supercontinuum and Spectrum Broadening in Holey Fibers Subjected to Radiation from Continuous Femtosecond Visible and Infrared Lasers

Supercontinuum generation in holey fibers manufactured at the University of Bath (Great Britain) and at the Institute of Radioengineering and Electronics of the Russian Academy of Sciences is produced through use of a Ti:sapphire femtosecond laser. Broadening of the radiation spectrum of a Cr:forsterite femtosecond laser ( = 1250 nm) is observed in these fiber samples. The present study is part of a program intended for the creation of an optical femtosecond synthesizer stabilized relative to a methane optical frequency standard ( = 3390 nm).     

Wood Fibre Reinforced Polypropylene Composites: Effect of Fibre Geometry and Coupling Agent on Physico-Mechanical Properties

Wood fibre reinforced polypropylene composites at fibre content 50% by weight have been prepared and different types of wood fibres (hard wood fibre, soft wood fibre, long wood fibre and wood chips) were treated with coupling agent (MAH-PP) to increase the interfacial adhesion with the matrix to improve the dispersion of the particles and to decrease the water sorption properties of the final composite.The present study investigated the tensile, flexural, charpy impact and impact properties of wood fibre reinforced polypropylene composites as a function of coupling agent and fibre length and structure.From the results it is observed that wood chips-PP composites showed better tensile and flexural properties comparative with the other wood fibre-PP composites with the addition of 5%MAH-PP, which is around 65% and 50% for tensile strength and flexural strength respectively. Hard wood fibre-PP composites showed better impact characteristic values comparative to other wood fibre-PP composites with the addition of 5%MAH-PP and damping index decreased about to 60%. Charpy impact strength also increased up to 60% with the addition of 5%MAH-PP for long wood fibre-PP composites. Water absorption and scanning electron microscopy of the composites are also investigated.     

飞秒激光与金膜作用的脉冲累积效应

采用1kHz飞秒激光（脉宽148fs,中心波长775nm）对石英衬底的金膜的烧蚀过程进行了研究．单脉冲与多脉冲的烧蚀阈值可以通过烧蚀点的直径平方与所用的激光能流的关系曲线获得．通过累积能流和烧蚀脉冲数的关系,可以得到金膜的脉冲累积因子．采用飞秒激光加工材料的一些特点可以合理解释单脉冲阈值附近获得的一些实验现象．     

纤维增强攻坚战斗部在混凝土中爆炸威力试验研究

为考核纤维增强攻坚战斗部在混凝土中的爆炸毁伤效应,对裸装药、复合材料壳体、钢壳体装药在混凝土靶中的爆炸破坏效应进行了对比试验研究。试验结果表明,同样装药情况下,裸装药爆炸产生的破坏区域大于复合壳体及钢壳体装药;复合材料壳体装药在阻抗匹配方面要比钢壳体装药好,更利于爆炸冲击波的传播;同样装药情况下,复合材料壳体装药爆炸对靶体爆炸驱动有效能量大于钢壳体装药。     

Drift of an Optical Fibre Gyroscope Caused by the Faraday Effect and Its Reduction by Use of a Polarizing Fibre

The drift of fibre gyroscopes caused by a magnetic field via the Faraday effect is formulated in a simple model with a polarizing fibre as a sensing loop. It is found that polarizing fibre, which has a extremely large loss difference between two polarization modes, can make the drift less than that with polarization-maintaining fibre. In this case, the drift is inversely proportional to the square of the loss difference. Although currently available polarizing fibre must be improved to have a larger loss difference, by using such a polarizing fibre or an absolute single-polarization fibre, we can reduce the requirement for shielding the magnetic field and/or the way of winding the sensing loop. The use of these fibres is attractive for applications that demand ultra-low drift, for example, geophysical applications.     

化学处理对熔石英表面抗激光损伤阈值的影响

分析了HF酸腐蚀时间对熔石英抗激光损伤阈值的影响.用浓度为4%的HF酸腐蚀15min后,测得熔石英抗激光损伤阈值提高了53.1%,并对其机理作了分析.激光损伤实验使用波长为355nm,脉宽为10ns,频率为3Hz的Nd:YAG调Q激光器测试系统.当泵浦激光辐照熔石英样品表面时,后表面比前表面更容易发生激光诱导损伤,HF酸腐蚀的程度对前后表面抗激光损伤阈值比基本没有影响.对实验样品在HF酸腐蚀前后表面粗糙度的测量结果表明,HF酸腐蚀时间较短时实验样品表面粗糙度基本无变化,如果选用的样品存在较多的表面及亚表面缺陷,当HF酸腐蚀去除掉重沉积层后,表面粗糙度将急剧上升.     

不同化学蚀刻法对石英基片激光损伤阈值的影响

为提高三倍频光学元件的表面损伤阈值,采用了不同方式对石英基片进行酸蚀刻,利用原子力显微镜观测了基片蚀刻前后的表面微观形貌,并在激光损伤测量装置上进行了R:1方式的阈值测试,比较分析了蚀刻前后基片激光损伤阈值和表面形貌的变化,并比较了不同抛光质量石英基片蚀刻效果的差异.通过实验研究,总结了不同蚀刻方式的优缺点,研究表明酸蚀刻法可以有效提高石英基片激光损伤阈值.     

Characterization of Frequency Stability: Effect of RF Filtering

This paper shows that the RF filtering of a signal generated by an oscillator affects the characterization of the frequency stability in a manner that differs from the filtering of the phase of this signal. The effect on both the frequency domain and the time domain measurement is considered. It is shown that the spectral density of the phase fluctuations of the filtered signal is a function of the spectral densities of the amplitude fluctuations and of the phase fluctuations of the original signal. The corresponding expression for the two-sample variance (Allan variance) is then also a function of these two contributions. Detailed calculation is made for the case of a signal with frequency stability limited by white phase noise and filtered by a first-order, low-pass filter. It is found that the frequency stability is improved by more filtering if the cutoff frequency, fc, is higher than the signal frequency, f0, as is the case for phase filtering. However, the stability will degrade with more filtering if fc < f0. An optimum frequency stability is reached when fc = f0/?2. Experimental measurements confirm these theoretical predictions.     

Properties of Wood Fibre-Polypropylene Composites: Effect of Wood Fibre Source

This study examined the effect of type of wood fibre source on the physical and mechanical properties of wood fibre-polypropylene composites. Wood flour, fibres of heat-treated wood and pellets were used as sources of wood fibres in the manufacturing process. All studied wood fibre-polypropylene composites were made from 75% wood, 22% recycled polypropylene (PP) and 3% maleated polypropylene (MAPP). Wood fibre-polypropylene composites were compounded in a conical twin-screw extruder. Water absorption and thickness swelling were studied. Mechanical properties of the composites were characterised by tensile, flexural, and impact testing. Micromechanical deformation processes were investigated using scanning electron microscopy done on the fractured surfaces of broken samples. The durability of composites exposed to three accelerated cycles of water immersion, freezing and thawing was examined. The results showed that the density of the composites was a key factor governing water absorption and thickness swelling. A significant improvement in tensile strength, flexural strength, and Charpy impact strength was observed for composites reinforced with heat-treated fibre compared to composites reinforced with pellets and especially to wood flour reinforced composites. The flexural strength and dimensional stability performance reduced after exposure to freeze-thaw cycling for all composites, but the degree of these changes was dependent on the wood fibre source.     

Effect of Ni on Sintering Characteristics of Short Cast Iron Fibre

Nickel,as the carrier through which Fe atomsdiffuse,obviously enhances the densification ofsintered compact containing short cast iron fibre.When Ni content is above 4.5 wt-% there are someaustenites in microstructure at room temperature,discontinuous cementite networks at the interfacesbetween austenites and pearlites,free graphite pre-cipitated in austenite and pores andWidmannst(?)tten carbide precipitated in austenite.When Ni content is about 12 wt-%,it leads to de-crease in densification ratio and change in fracturemorphology of sintered compact from ductile tobrittle.     

激光在微电子器件制造中的应用

本文比较系统地介绍了激光在半导体微电子器件制造中的应用。对准分子激光器与光刻技术、激光图形发生,全息掩模与硅片检测、掩模缺陷激光修补与激光化学气相沉积,以及其它方面的一些激光应用作了比较详细的叙述。     

试样厚度对碳纤维复合材料拉伸力学性能的影响

本文对两种不同厚度的碳纤维复合材料进行了力学性能试验,并对其断裂过程及性能进行了对比分析。结果表明:厚度为1.40 mm的碳纤维复合材料比厚度为3.00 mm的碳纤维复合材料力学性能优越,其断裂后的纤维股比较细,纤维股完全发生断裂,贡献出其所有的应力;而厚度为3.00 mm的碳纤维复合材料断裂后的纤维股都比较粗,纤维辅层之间未能完全发挥到其极限应力。厚度为1.40 mm的碳纤维复合材料比厚度为3.00 mm的碳纤维复合材料的抗拉强度平均提高了65%;弹性模量提高了8.8%;延伸率提高了0.5%。     

层状黏土材料对导水纤维涂层脱附水性能的影响

涂层导水纤维是导水纤维复合薄膜材料的实现水分子可控缓释的关键,涂层材料中的添加剂选用层状黏土.本工作通过比较不同涂层导水纤维的渗水规律,研究了普通黏土、高岭土、膨润土三种黏土添加剂对导水纤维涂层脱附水性能的影响.实验采用Perkin Elmer Diamond SⅡ综合热分析仪、Cambridge Instrucment STEREOSCAN360扫描电镜、M30快速水分测定仪等检测设备,研究了不同涂层导水纤维的结构和持水能力以及涂层导水纤维的吸附和脱附水分子的规律.实验结果表明这三种黏土都能实现涂层导水纤维对水分子的可控缓释性,其中添加剂T(普通黏土)处理的涂层导水纤维在实现分子传水可控性上要优于其他两者.