激光光强分布测量中面阵CCD信号畸变的校正

当面阵ＣＣＤ用于激光能量空间分布测量时，由于ＣＣＤ探测器光电响应非线性、光电响应非均匀性等因素影响，必然使信号产生畸变。本文通过理论分析与实验对畸变进行了校正，收到了良好的效果。     

Measurement of Atmospheric Turbulence Induced Intensity Fluctuations in a Laser Beam

We report measurements of the statistical properties of the intensity fluctuations in a He/Ne laser beam which had propagated 1·125 km through the earth's atmosphere. The beam size was such that the beam propagated as a spherical wave, and atmospheric conditions such that most measurements were made in the ‘saturation’ region (β₀ ～ 1-4). We found (1) that the variance of the intensity was considerably larger than that previously reported for plane wave propagation, and (2) that the probability distribution of the intensity and the derived moments were close to the K-distribution and its moments. The origin and significance of the K-distribution in atmospheric propagation is considered. Photon counting techniques were used for all measurements.     

Knife Gauge for Measurement of the Intensity Distribution in a Beam of Optical Radiation

A method of measuring the distribution of the intensity of optical radiation in space is described. The method consists in measurement of the power reflected from a specially shaped knife that moves perpendicular to the direction of propagation of the beam or that passes through a moving diaphragm provided with a hole.     

The Intensity Distribution of a Gaussian Schell-model Beam Focused by an Aperture Lens

Abstract

Starting from the generalized Huygens-Fresnel diffraction integral, we study the intensity distribution of a Gaussian Schell-model (GSM) beam diffracted at an aperture lens. A great number of numerical calculations have been performed to illustrate the focused field characteristics. Isophote diagrams are given for systems of different Fresnel numbers, which focus GSM beams, and the related analysis is presented.     

声强空间分布及水听器灵敏度标定误差分析

在非开阔水域中采用比测法标定水听器灵敏度时,声源附近的声强空间分布因多途声波相干叠加呈现分层特点,引起水听器灵敏度标定结果存在系统性误差.声场仿真和垂直阵实测证实了声强分层现象,解释了在非消声水池中进行水听器灵敏度标定试验的误差成因.提出在消声水池或开阔水域进行灵敏度标定试验,并将水听器和标准小球同深度布设,可消除声强...     

激光光束中微粒散射的散射光能分布研究

文章通过对角散射粒度分析方法的数学建模,研究了处于激光光束中的微小颗粒对光的散射能量分布,研究表明,在微粒粒径较大(d＞5λ/π),沿着光入射方向上的正向±π/4和负向±π4范围内,具有最大的散射能量分布,但这一结果并不适用于小粒径微粒.     

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.     

Intensity Fluctuations in a Two-mode Ring Laser

Intensity fluctuations in a two-mode ring laser with zero detuning are derived using a noise amplification rate-equation model. Both approximate and exact forms of the gain saturation are treated. Steady-state distributions of the intensity are derived analytically permitting calculation of the mean and normalized variance. Numerical solutions yield the time-dependent evolution of these quantities from initial input noise. Recently derived mode competition effects, such as a steady state value of } for the normalized variance (rather than zero as in a conventional laser) and negative correlations between the intensity fluctuations of the two modes, appear more simply here and their statistical origin is explained.     

Influence of Conversion Nonlinearity of a Bolometer on the Results of Measuring Nonuniformity of the Intensity Distribution of Laser Radiation

A derivation is given of the dependence of the nonuniformity coefficient of the intensity distribution of laser radiation, measured using a profile bolometer transducer, on the nonlinearity of the bolometer conversion characteristic and the effective power level or effective specific energy. The random error of the measured coefficient is estimated.     

Deposition of Laser Mirrors by Laser Beam Evaporation

A 200W c.w. CO₂ laser has been used to evaporate thin multilayer films of HfO₂-SiO₂ and ZrO₂-SiO₂. Higher values of laser damage resistance were found compared to similar layers produced by electron-beam evaporation.     

Neural Networks-Based Real-Time Determination of the Laser Beam Spatial Profile and Vibrational-to-Translational Relaxation Time Within Pulsed Photoacoustics

This paper concerns with the possibilities of computational intelligence application for simultaneous determination of the laser beam spatial profile and vibrational-to-translational relaxation time of the polyatomic molecules in gases by pulsed photoacoustics. Results regarding the application of neural computing through the use of feed-forward multilayer perception networks are presented. Feed-forward multilayer perception networks are trained in an offline batch training regime to estimate simultaneously, and in real-time, the laser beam spatial profile (profile shape class) and the vibrational-to-translational relaxation time from given (theoretical) photoacoustic signals. The proposed method significantly shortens the time required for the simultaneous determination of the laser beam spatial profile and relaxation time and has the advantage of accurately calculating the aforementioned quantities.     

Surface Hardening of Alloy Steels Using a High Intensity Electron Beam

Energy sources such as electron or laser beams have been extensively used for materials processing. Surface hardening is an established process used in industry. A combination of nitriding and electron beam treatment is used to modify alloy steel with nominal composition (wt.%) of 0.42% C, 0.96% Cr, 0.6% Mn, 0.37% Si, balance Fe. The hardness of the hardened layer varies in the range 800-850 HV. The high hardness is due to a refined microstructure consisting of a -solid solution (nitrous martensite) and γ - solid solution (nitrous austenite) and dispersed fine nitride precipitates. The wear resistance the of electron beam treated layer is double that of the ion nitrided specimens.