应用激光微小光斑进行颗粒分析

目前已有多种颗粒分析的方法,它们都有各自的特点,本文介绍一种应用激光微小光斑进行颗粒分析的技术,该方法应用聚焦光斑直径与被测样品平均颗粒粒径相近的激光光斑,使其落在样品颗粒上,在后向获取信号,经处理得到样品颗粒分析的结果,它适用于河道与港口水样品的泥沙分析,也可以应用在类似的场合。     

粉末倍频纵向位置效应的研究

基于Kurtz粉末倍频测试原理,在固定的基频光波入射方向下,通过改变探头相对于样品的纵向距离,对粉末倍频(SHG)纵向位置效应进行了研究。实验结果及数据拟合表明,在一定的粉末粒径和粉末堆积厚度下,碘酸钾晶体粉末和尿素晶体粉末的相对倍频光I~(2ω)均随探测距离S成指数衰减,碘酸钾粉末与尿素粉末的二次谐波信号的相对大小不随探测距离变化,且在5.8%的标准误差范围内,测得碘酸钾粉末倍频效应是尿素粉末倍频效应的6.8倍。     

激光烧结成型用复合尼龙粉末的制备及性能测试

介绍了尼龙粉末材料的激光烧结成型技术研究现状,研制开发了一种适用于激光烧结快速成型的复合尼龙粉末材料(CPP1),并对其主要性能进行了测试;在优化的工艺实验条件下,制作了激光烧结成型尼龙件,进行了力学性能测试,其强度接近国外同类产品水平,韧性高于国外水平,可以满足新产品开发的要求.     

粉末材料激光烧结过程温度场的测试系统

介绍了粉末材料的激光烧结成型技术,对粉末材料激光烧结成型的加热过程进行了分析,在此基础上研制了一种适合于粉末材料激光烧结成型过程温度场的测试系统,利用红外测温仪测量粉末表层温度,利用热电偶测量粉末内部温度,测量结果由计算机打印输出.     

一种粉末倍频的实验装置研究

为了研究非线性材料的倍频效果,提出了一种粉末倍频（SHG）测量装置,它采用光纤光谱仪来代替一般的光电倍增管,同时测量出基频光和倍频光的光信号,既克服了光源的波动,又大大减小了噪声的影响,增强了测试的可靠性。通过与其他方法的测量结果比较,很好地验证了装置的可行性。     

CCD中的激光光斑阴影现象及机理

对CCD相机在激光辐照下的暂时性失真问题进行了研究.用532 nm连续激光辐照以线阵CCD为图像传感器的Piranha HS-41-02K30相机进行了实验,实验发现,激光光斑和3个与其大小、形状皆相似的暗斑同时、等间距地出现于感光阵列方向上.这些暗斑即为CCD相机在激光辐照下的一种暂时性失真现象,本文称这3个暗斑为光斑阴影.根据实验数据分析了这一现象的规律和产生机理.分析认为,CCD图像传感器4个并行读出电路因共用同一偏置源而相互影响是产生光斑阴影现象的内在机制.推导了共偏置并行电路信号之间相互影响的关系式,由得到的关系式可知,降低公共偏置源与并行读出电路公共节点之间的电阻可减弱上述阴影失真现象;而用4个电压源分别为并行读出电路提供偏置,可以消除这种光斑阴影现象.本文推导的共偏置并行电路影响关系式不仅可解释阴影现象,也可为设计CCD器件时减弱或消除阴影失真提供借鉴.     

外场激光光斑中心检测算法研究

激光光斑中心检测是光学测量中常用的关键技术。检测算法的精度及速度直接影响了测量的精度及速度。针对外场环境下干扰较强的特点,研究了重心法、Hough变换法以及圆拟合算法,通过理论分析与实验,提出一种改进的激光光斑中心检测算法,提高了中心检测的精度、速度及抗干扰性,可用于外场环境的实时光学测量。     

高斯拟合光斑定位算法推导及性能探讨

为了解决混凝土结构挠度测量中参考点精确定位的问题,推导了高斯光斑的拟合算法,证明了参数克拉美-罗下界的存在,并利用莱文贝格-马夸特方法优化了相应参数。实验结果表明,基于非线性参数优化的高斯拟合光斑定位算法在信噪比为40 dB时,其中心提取的均方根误差衰减为0。随着对比度的降低,3种测试方法的提取精度会变差。在对比度降至原图像的25%之前,基于非线性参数优化的高斯拟合光斑定位算法的鲁棒性优于其他算法,但当对比度继续下降时,这一优势将消失。因此,在对比度良好的情况下,该算法不仅可以保证精度而且可以较好地提高鲁棒性。     

选择激光烧结粉末的参数分析

选择激光烧结粉末生成三维零件，是90年代发展起来的崭新的制造技术。本文从激光系统、扫描系统和粉末系统三个方面对粉末的烧结参数进行了分析，为这些参数的优化提供了理论依据。     

基于MATLAB的激光光斑图像处理算法

提出了一种基于MATLAB的激光光斑图像处理仿真算法.在MATLAB环境下,首先对采集到的光斑图像进行平滑滤波、亮度调节、阈值分割和边缘检测等图像处理,确定出光斑区域并得到边缘点的位置信息,再根据最小二乘法进行圆拟合进而计算得到光斑中心点的坐标.仿真结果表明,该算法能够快速、准确地得到光斑中心位置点,且达到很高的测量精...     

High second harmonic generation signal from muscles and fascia pig's muscles using the two-photon laser scanning microscope

I have provided update to our two photon laser scanning microscope by adding new technique which enables us to simultaneously measured the second harmonic generation signals in the forward and backward directions; in the meantime, one can measure the two photon excitations fluorescence if the materials produce fluorescence. In the present work, the fascia muscles, muscles of pig and pig's skin were used. I found that these materials produced high second harmonic generation signal in both directions. These measurements show that the second harmonic generation strongly depends on the state of the polarization of the laser light and the orientation of the dipole moment in the molecules that interact with the laser light. It is therefore advantageous to control the laser's state of polarization, to maximize second harmonic generation. The novelty of this work is to establish new multi-functional technique by combing three platforms of laser scanning microscopy – the fluorescence microscopy, harmonic generation microscopy and polarizing microscopy in which one can use the second harmonic imaging to investigate the true architecture of the sensitive samples and the samples which do not produce auto-fluorescence. Moreover investigation of the new sample needs to look at all details of the true architecture of the sample. Thereby the sample will be exposed to the laser radiation more than the well-known sample, and that will cause photo-bleaching and photo-damage. Since the second harmonic generation does not undergo from photo-bleaching and photo-damage it will be the promising technique for investigating the sensitive and new samples. Then one can move to acquire fluorescence images after good investigation of the true architecture of the sample by the SH imaging.     

Second harmonic generation imaging of the deep shade plant Selaginella erythropus using multifunctional two‐photon laser scanning microscopy

Background : Multifunctional two‐photon laser scanning microscopy provides attractive advantages over conventional two‐photon laser scanning microscopy. For the first time, simultaneous measurement of the second harmonic generation (SHG) signals in the forward and backward directions and two photon excitation fluorescence were achieved from the deep shade plant Selaginella erythropus. Results : These measurements show that the S. erythropus leaves produce high SHG signals in both directions and the SHG signals strongly depend on the laser's status of polarization and the orientation of the dipole moment in the molecules that interact with the laser light. The novelty of this work is (1) uncovering the unusual structure of S. erythropus leaves, including diverse chloroplasts, various cell types and micromophology, which are consistent with observations from general electron microscopy; and (2) using the multifunctional two‐photon laser scanning microscopy by combining three platforms of laser scanning microscopy, fluorescence microscopy, harmonic generation microscopy and polarizing microscopy for detecting the SHG signals in the forward and backward directions, as well as two photon excitation fluorescence. Conclusions : With the multifunctional two‐photon laser scanning microscopy, one can use noninvasive SHG imaging to reveal the true architecture of the sample, without photodamage or photobleaching, by utilizing the fact that the SHG is known to leave no energy deposition on the interacting matter because of the SHG virtual energy conservation characteristic.     

SLM铺粉设备的误差分析及控制方法

自行设计、制造了一套铺粉装置。介绍了该铺粉装置的主要组成和工作原理;重点分析了铺粉装置的误差来源:如刮板刃口的直线度和运动误差、成型缸活塞运动误差、基板平面与推动丝杠轴线的垂直度等。提出了误差的计算方法,重点论述了刮板运动误差的放大效应,给出了计算公式。实践表明:可以通过采用专业高精度线性模组等措施控制、消除误差。     

激光自动对焦中离焦量的探测与计算方法

根据激光光线聚焦状态不同对应被测面上激光光斑形状不同的特点,通过引入辅助激光束,分析了调焦CCD采集的激光光斑图像信息,进而根据光斑形状及半径等信息确定被测面对焦状态。针对实验中每隔相同离焦距离采集的一系列光斑图像,提出了相应的图像处理方案,以提取所需光斑半径信息,进而进行光斑半径与离焦量转换。实验结果表明,光斑半径与离焦量呈线性关系,最大线性范围灵敏度为2.342像素/μm,最高可实现0.43μm分辨率。     

基于旁瓣光束衍射反演的强激光远场焦斑测量方法

针对大型激光装置使用纹影法无法实现旁瓣光束弱信号区域光强分布精确测量的问题,提出了基于旁瓣光束衍射反演的纹影法强激光远场焦斑测量方法.采用逆向推演间接测量的研究方法,沿光路传播逆方向推导,以旁瓣光束衍射光强图像和相位图像作为输入,通过计算获得未遮挡前旁瓣光束远场焦斑分布.相比传统基于纹影的远场焦斑测量方法,本文的主要改...     

提高外场脉冲激光光斑测量距离的有效方法

介绍了提高外场脉冲激光光斑测量距离的两个关键技术:CCD电子快门预测和背景相减技术, 并给出了提高白天外场脉冲激光光斑的测量距离的试验效果,在激光制导武器系统和激光告警系统的研制中都有重要的意义.影响白天外场对脉冲激光光斑的测量距离的主要原因是激光光斑被淹没在阳光照射的背景里,不能提取光斑图像.设法让电子快门的触发脉冲在每个激光脉冲到来前的固定时间间隔产生,保证CCD捕捉到光斑的全部能量,从而可以使CCD输出最亮的光斑图像.另一方面,在激光没有照射时,采集一帧图像作为背景, 让激光照到靶板后的图像与背景图像相减,结果只在光斑照到的位置处有不同.在相减后的图像中,使激光光斑突出.试验证明采用本文介绍的技术明显地提高了外场脉冲激光光斑测量距离.     

Orientation effect of electropolishing characteristics of 316L stainless steel fabricated by laser powder bed fusion

Frontiers of Mechanical Engineering - 3D metal printing process has attracted increasing attention in recent years due to advantages, such as flexibility and rapid prototyping. This study aims to...     

Spectral characteristics of autofluorescence and second harmonic generation from ex vivo human skin induced by femtosecond laser and visible lasers

The spectral properties of one-photon, two-photon excited autofluorescence and second harmonic generation (SHG) from ex vivo human skin induced by a femtosecond (fs) laser and three visible lasers in backscattering geometry are systematically investigated. Our experimental results indicate that peak position of autofluorescence spectra from the dermis and epidermis shift toward long wavelengths, and the fluorescent intensity decreases when the excitation wavelength increases due to an effect of the excitation wavelength on autofluorescence signals. However, the intensity of the SHG signal in collagen has the maximal value of 800 nm excitation wavelength. This may be the result that the energy of the SHG signal is in resonance with an electronic absorption band. The two-photon excited autofluorescence and SHG intensity all obey a quadratical dependence on the excitation power. Compared with the two-photon excited fluorescence and SHG, the one-photon excited fluorescence in the dermis and epidermis exhibits different spectral characteristics. The investigation of the spectral characteristics of autofluorescence and SHG from ex vivo human skin can provide new insights into morphologic structures and biochemical components of tissues, which are vital for improving the application of laser-induced autofluorescence and SHG spectroscopy technique for noninvasive in vivo tissue diagnostics.     

Linear rugosity concept of crystalline surfaces by using the unidirectional laser oblique illumination (ULOI) technique.

The study of the I(phi) curves obtained with Unidirectional Laser Oblique Illumination describes the roughness of a crystal as a combination of straight edges in different directions, which generate the concept of linear rugosity. In the present work, a model of the crystalline surface based on this concept is introduced. Diffraction gratings as well as metallic surfaces subjected to different metallographic procedures are analyzed. The theoretical results are compared with experimental values obtained in samples of Fe and Zn using an objective of 16x. Both values, theoretical and experimental, are in total concordance.