On the Scattering Matrix of Multimode Fibres for Polarization Recovery by Phase Conjugation

Abstract

A phenomenological model for the scattering matrix of a long mode-scrambling optical fibre is derived, predicting incomplete polarization information recovery using a single-polarization phase-conjugating mirror at the fibre output, in agreement with some recent experimental findings.     

CTP激光光源及技术分析

激光技术对于计算机直接制版CTP来讲尤为关键。本文从电磁波谱、激光器的组成和激光器的类型三个方面对激光技术作一介绍,使广大印刷工业者对激光技术有进一步的了解。然后介绍了现在CTP领域常用激光光源,并对各种光源技术进行比较分析。     

Range-dependent Optical Feedback Effects on the Multimode Spectrum of Laser Diodes

Abstract

Weak optical feedback from diffusely-reflecting objects can dramatically affect the optical spectrum of homogeneously-broadened laser diodes operated near the lasing threshold. Switching between two or more oscillation modes can be controlled by as little as 1 nW of optical feedback power. The modulation effects on the optical spectrum and total power output depend on the phase of the returned light, and the strength of the effect has a range dependency that is useful for metrology applications. In the present work, experimental and theoretical analyses of these phenomena are presented, and a simple metrology tool for position sensing and remote surface profiling is proposed.     

高能超声分散纳米晶须的数值和物理模拟

为研究高能超声处理制备纳米复合材料过程中纳米增强相在熔体中的分散过程,采用甘油为介质分别进行了数值模拟以及物理模拟。数值模拟结果表明,当超声作用于甘油中时,甘油中会形成中心-底面-壁面-中心的环形流动,变幅杆探头端面边缘附近甘油流体存在最大的流动速度,且随着超声功率的增大,流体运动速度增大。物理模拟实验结果显示,高能超声作用下甘油的实际运动行为与数值模拟结果相符合,存在环形流动;此外,高能超声作用下甘油中存在明显的空化效应;纳米晶须在超声作用下于甘油中分散良好,且随着超声功率的增大,达到充分分散所需时间变短。     

Some High Intensity Flash Light Sources of the Luminescent Tube Type

The design and performance of vacuum flash tubes of the cathode ray tube type are described in which short-duration impulses of a high-energy electron beam are used to excite a phosphor screen and thus to produce luminescent radiation pulses of high intensity. Triode type tubes are shown which may be operated with 2kW pulses, and a diode type tube is described where the screen may be energized with I MW pulses. Either single-pulse radiation or trains of pulses with short pulse intervals can be produced, the duration of an individual radiation pulse ranging from about 0.1 microsec to the order of 100 microsec according to the rated value of the respective flash tube. The spectrum of the radiation is continuous with a form of the spectral curve depending on the type of phosphor used for the screen.     

Nd：碲酸盐玻璃的光谱和激光性质

对比了各种激光玻璃的光谱性质，指出碲酸盐玻璃是一咱理想的激光介质，并资产在室温下实现了钛宝石激光器泵浦了Ｎｄ：碲酸盐块体玻璃的激光发射，激光阈值４．２０ｍＪ，斜率效率１４．７％。     

医用激光源的工作参数和检测过程中的注意事项

本文结合实际检测工作,介绍了医用激光源的分类、参数以及操作时需注意的地方.     

Confinement of Electrons to the Centre of a Laser Focus Via the Ponderomotive Potential

Abstract

The use of the ponderomotive potential to focus electrons into the centre of a laser focus, as discussed by Phillips and Sanderson in 1966, is examined for modern laser conditions. For a laser focus with a minimum along the beam axis, an electron is confined to the centre of the focus. Electron trajectories are obtained by solving the classical equations of motion in the presence of the ponderomotive potential. A method of creating a focus with a minimum at the centre is also discussed.     

Finite Element Analysis of Laser Cut Edge Beam Section for High Stress Intensity Structural Assessment

This research has analyzed the stability of laser cut-edges in the location of high stress intensity of a structural beam. The cut-edge characteristic properties formed during laser-cutting processing have been over prolonged periods determined to have beneficial effects on fatigue life. During this study two high strength steel grades S355MC and DP600 have been examined. Optimal fatigue lives were attained by minimizing the laser cut-edge surface damage, maintaining the formation of shallow striations and by controlling the near edge microstructural deformations during the cutting process. This was validated using a bespoke component in which was tested under four-point loading in which there is a area of stress concentration forming a localized plastic zone. The importance of this region is critical due to the fact that it is the area that influences the fatigue life of the structure. Predicting the lives to crack initiation was determined through FE analysis which is based on the use of E–N cut-edge fatigue data.     

湍流大气中激光强度和相位的统计特性

运用激光大气传播双随机场模型、等概率密度椭圆方法和引入“椭圆度”参数研究了湍流大气中传播激光光场的强度和相位的概率分布,得到了椭圆高斯分布散射光场的相位和光强的概率密度函数解析式以及弱湍流起伏区域的光波相位差概率密度函数解析式。     

直方图法在雷达故障数据统计分析中的应用

提出了直方图的绘制方法、步骤以及主要类型,运用此方法在雷达故障数据统计中进行分析应用,为雷达装备维修提供重要依据.     

New Method for Optical Pumping of a Solid State Laser through the Use of Light Fibres

The present work is concerned with the theoretical design and investigation of a new system for optical pumping of solid state lasers. The originality of the new system lies in the use of optical fibres to transmit the light from its source to the laser-active material, thus allowing complete spatial separation of the two. The degree of uniformity achieved in illuminating the surface of the laser material is theoretically investigated and is shown to be very high. The efficiency of the system is also examined and the resulting advantages and disadvantages are pointed out. The possibilities for the realization of such a system are discussed and various ways of construction are proposed.     

On the Characterization of Polychromatic Sources That Generate the Same Intensity at the Output Plane

For general dispersive optical systems, the relationship that must be satisfied by all the cross-spectrally pure planar sources that generate identical intensity distributions at the output plane is derived. Also, a number of polychromatic planar sources producing the same intensity at the output plane are presented.     

Spectral Shift of Quantum-Cascade Laser Emission under the Action of Control Voltage

Technical Physics Letters - Spectral redistribution of the intensity of short- and long-wavelength emission components within gain bandwidth of a 7- to 8-μm quantum-cascade laser under the...     

表面形貌与位置对激光位移传感器接收光强的影响

根据被测物体表面反射模型，从理论上分析了表面形貌及其位置对激光位移传感器物镜接收光功率的影响。通过计算机模拟的方法，优化了传感器的入射角     

A Comparison of Q-Switched and Intensity Modulated Laser Pulses for Ultrasonic NDT

The purpose of this work was to investigate the potential of intensity modulated laser pulses for ultrasonic signal enhancement in NDT using a numerical model. Q-switched lasers produce broadband ultrasound which is susceptible to measurement noise. Intensity modulation can alleviate this problem by focussing the ultrasonic energy into a band centered around the modulation frequency. Ultrasonic waveforms and their DFTs are considered here in both aluminum and steel for a wide range of observation angles, for Q-switched laser pulses and for a 1 MHz intensity modulated laser pulse. These waveforms are useful to NDT researchers becauses they indicate what kinds of signals can be expected from unflawed materials. It is found that P waves are not as easily enhanced by modulation as are SV or Rayleigh surface waves. The time window which should be used to measure ultrasonic signals produced by intensity modulated laser pulses is determined.