动态激光衍射法测量细丝直径

基于夫琅禾费衍射理论和巴比涅互补原理,提出了利用激光衍射对细丝直径进行动态测量的方法.该方法具有测量精度高、速度快、非接触、使用方便且易于微机联接实现自动化测量等优点.     

利用Matlab实现RGB三基色法测量细丝直径

基于衍射原理,实现RGB三基色法测量细丝直径。先通过实验得到细丝衍射图像,然后利用Matlab编写程序及设计界面处理RGB图像,最终计算出细丝直径。测量结果与其他方法相比具有测量精度高、速度快、非接触、使用方便等特点。     

金属光学性质对高精度丝径测量中偏振效应的影响

本文主要研究金属细丝的光学性质对高精度丝径测量中偏振效应的影响,由振动平行和垂直于细丝轴线的偏振光的夫琅和费衍射图样得到的丝径值不相同,理论分析表明:这种丝径的差值与金属复数折射率的虚部近似成正比关系增大,而与它的实部无关,一些实验结果与理论分析符合得很好。     

圆柱体的空间圆锥光反射、折射与衍射

用准直或会聚激光束倾斜照射圆柱体时,其反射光、透射光(柱体透明时)、衍射光(柱体较细时)的叠加将形成以光束入射点为顶点的空间圆锥形光面(空间光锥),并且在垂直于柱体轴线方向的观察平面上投影成一圆形光环.空间光锥的形成与所选圆柱体材料及其粗细无关,只要其表面具有一定反射能力即可.空间光锥的锥角等于入射光束主光轴与圆柱体轴线夹角的2倍,与圆柱体和照射光束的直径大小及光波长无关.给出了对光纤及不同直径大小的玻璃和金属圆柱体的实验观察结果,并利用矢量图解法对其进行了详细地理论分析.进而得出,通常所谓单丝衍射图样,实际上是细丝的衍射和其表面的反射光场的叠加图样,对于透明细丝,还包括其透射光场的贡献.圆柱体的这种空间圆锥光反射和衍射原理有可能用于光束定位、成形、表面检测以及三维面形测量等 关键词： 圆柱体 空间光锥 投影光环     

高精度丝径测量中的偏振效应

本文主要研究光束偏振方向对高精度丝径测量的影响,将给出简要的实验结果:钢丝直径的实测值随光振动方向与细丝轴线的夹角呈正弦变化;振动平行细丝轴线的偏振光的实测值比垂直的小0.36μm;钢质狭缝宽度测量结果则与钢丝情况相反。在此基础上着重对这种影响进行了理论分析。计及细丝表面反射和不同偏振方向光波反射时产生的不同位相变化,细丝的夫琅和费衍射图也发生了微小的改变,致使直径测量值不同。由此对钢丝的分析表明：光振动平行千丝轴时的直径理论值比季直的小0.33μm，与实验值0．36μm。相差0．03μm；光振动平行缝边时的宽匿理论值比垂直的大0．19μm，与其实验值0．21μm相差0，02μm。它们都接近或小于仪器的测量误差0．04μm，理论与实验符合得很好．     

测量线胀系数的一种新方法

给出测量金属线胀系数的一种新方法。本文根据夫琅和费衍射原理，利用CCD来测量金属体随温度升高的伸长量，对黄铜的线胀系数进行了测量。     

光的衍射法测量金属的线胀系数

给出测量金属线胀系数的一种新方法．利用光的衍射法可以较精确地测量长度变化这一特点，对黄铜的线胀系数进行了测量．     

细丝Fresnel衍射光强分布函数的推导

本文给出了Ｆｒｅｓｎｅｌ积分的函数解，并推导出细丝Ｆｒｅｓｎｅｌ衍射的光强分布函数。     

数字激光散斑照相技术测金属杨氏模量

介绍了利用数字激光散斑照相技术测量了金属细丝的杨氏模量的方法.该方法将激光散斑随着金属丝的伸长而变化的过程用数字记录设备(CCD)拍摄下来,通过计算机程序对采集到的图像进行处理,并获得2张激光散斑图的干涉条纹,从而得到金属细丝伸长量并计算出相应的杨氏模量.该技术能够实现金属材料杨氏模量的自动测量,保证了测量过程的快速稳定,提高了测量精确度.     

微细金属丝在空气中的自然对流换热的实验研究

对直径分别39.9～350.1 μm的微细金属丝水平和垂直放置在空气中时的自然对流换热系数进行了实验测量.实验中对细丝采用焦耳加热.并通过标定金属丝电阻与温度的关系,精确测定了金属细丝的表面平均温度.将测得的实验值与经典关联式的预测值进行了比较,实验结果表明:随着细丝直径的减小,实验值与理论计算值的差别越来越大.这可能由于尺度的缩小,使得细丝的边缘效应加强,边界层变薄,从而强化了换热;水平放置的细丝表面的自然对流换热要强于垂直放置的细丝,这是由于竖丝表面受到流体的冲刷作用,边界层厚度大于横丝表面边界层厚度的缘故.     

基于飞秒激光等离子体丝诱导击穿光谱探测土壤重金属Cr元素含量

本文基于飞秒激光等离子体丝诱导击穿光谱对土壤重金属Cr元素含量进行了实验研究.利用荧光法对等离子体丝的长度进行测量,给出了在不同焦距聚焦透镜作用下土壤中Cr425.5 nm的谱线强度空间分布,实验给出了Cr元素的定标曲线.实验结果表明,土壤中Cr元素浓度分析测量的相对标准偏差小于5%,土壤中重金属Cr元素的检测极限为7.85 ppm.表明飞秒激光等离子体丝诱导击穿光谱技术在土壤重金属Cr元素含量的定量探测方面是完全可行的.     

Filamentation of ultrashort light pulses in a liquid scattering medium

We have studied filamentation of 1-ps laser pulses in a scattering medium (aqueous suspension of 2-μm polystyrene microspheres) and compared filamentation dynamics to that in pure water. Our results indicate that light scattering does not alter filamentation dynamics in general, but rather results in farther position of the nonlinear focus, shorter filament length, and the development of speckle structure in the peripheral part of the beam. The experimental observations are qualitatively reproduced by the numerical model which accounts for diffraction, self-focusing, multiphoton absorption, and light scattering introduced through a stochastic diffusion and diffraction term.     

The influence of divergence on the filament length during the propagation of intense ultra-short laser pulses

We have questioned the conventional criterion, which is the critical power for self-focusing, to predict the stopping position of a filament. Our experimental result suggests that during the filamentation process the plasma induces an additional diffraction of the laser beam. This is another crucial factor that may lead to the termination of the filament even if the power is still much higher than the critical power. This should be taken into account in order to estimate the end of the filament as well as its length. PACS 52.38.Hb; 42.65.Jx; 52.35.Mw     

CVD金刚石薄膜的应力研究

 利用X射线衍射研究了化学气相沉积的金刚石薄膜的应力情况。研究表明：热应力在研究范围内为压应力，本征应力是张应力。分析了薄膜厚度、生长温度、碳源浓度等实验参数对薄膜应力的影响。     

金属单层膜的小角X射线衍射强度的研究

本文对金属单层膜进行研究,在多种样品中没有发现X射线衍射峰.我们在基底上预先淀积一层重金属膜,然后再淀积所需样品,发现样品有较好的衍射峰产生.我们对此进行了探讨并提出了一个可能的理论定量解释.     

Control of lasing filament arrays in nonlinear liquid media

Multiple filamentation in a high concentration solution of coumarin 153 in ethanol is studied. It is shown that the output filament pattern may be controlled by placing diffractive elements (circular aperture, edge) in the input beam path. These filaments are formed in highly reproducible arrays along diffraction maxima corresponding to the element used. Experimental results are supported by numerical simulations. They confirm that diffraction-induced intensity gradients swamp modulational instability on the wavefront, forcing filaments to form along diffraction maxima. The effect of two-photon absorption by coumarin molecules on filament patterns is also investigated over a range of dye concentrations. Control results are finally exploited in the production of arrays of localized lasing filaments, which should open novel applications. The resultant lasing sources are mutually coherent and highly repeatable from shot-to-shot, as is shown by their far-field interference patterns. PACS 42.65.Tg; 52.38.Hb; 42.68.Ay     

Enhancement of third harmonic emission by interaction of two colored filament with droplet in air

Numerical simulations are performed to investigate the third harmonic emission from femtosecond laser filament, center of which is blocked by a droplet. It is shown that sudden stop of fundamental laser filament induced by the droplet leads to the enhancement of third harmonic emission. The diffraction on droplet leads to the increase of third harmonic energy in background reservoir which can be survived after the dissipation of filament.     

1kHz飞秒激光脉冲在空气中传输成丝的演化过程

利用高重复频率(１kHz)、低能量的飞秒激光脉冲研究激光脉冲在空气中传输成丝的演化过程.采用成像的方法观测飞秒激光脉冲在大气传输过程中光束截面上光强分布变化，以及大气等离子体通道对光强分布的反作用.实验结果表明，激光脉冲在传输过程中先形成双丝结构，再逐渐合并成单丝结构.实验结果与利用非线性薛定谔方程耦合多光子电离的数值模拟结果基本一致. 关键词： 飞秒激光脉冲 等离子体通道 成像     

Current transport in bistable granular structures

Electrical breakdown in GaAs Schottky diodes creates a granular filamentary structure of submicron dimensions between the contacts. The filament exhibits very fast (<2 nsec) electrical switching between stable resistance states. Irrespective of the contact metal, the filament becomes superconducting when in the low-resistance state. Electron transport in all the resistance states is intergrain tunneling between metallic inclusions and is governed by an activation energy. Switching is not based on metal transport.