激光光强扰动对相干场成像降质影响理论研究

激光相干场成像系统发射多束激光,经大气传输对远程目标成像,大气湍流引起的激光束光强扰动是影响成像质量的一个关键因素.本文从湍流引起的激光束光强扰动对回波解调信号的影响关系入手,建立了激光回波光强扰动因子对相位闭合系数和成像频谱分量的降质传函理论模型;基于三光束激光相干场成像系统仿真验证了理论模型的有效性.研究表明激光相干场成像频谱分量和成像像质主要受三光束相位闭合求解算法中第二光束光强扰动影响.该研究揭示了激光回波光强扰动对成像像质的影响机理,对于分析大气湍流等引起的光强扰动降质效应和合理分配多光束光强稳定性以提高成像质量具有理论指导意义.     

1.54 THz激光成像实验与物质穿透特性

 用1.54 THz的波导型辉光放电激励的大功率连续波氰化氘（DCN）激光系统,进行了1.54THz激光成像实验研究和多种物质的穿透特性研究。利用简单的被测物体的2维扫描光学系统进行了连续波1.54 THz激光物体穿透成像,通过测量穿透光的不同强度清楚地识别了放入信封的塑料胸卡和金属硬币的位置和形状。实验中对不同物质进行了1.54 THz激光穿透特性测量,得到了多种不同物质的吸收系数。     

漫透射成像法激光强度时空分布测量装置

 提出用CCD漫透射成像法测量激光强度时空分布和激光功率,给出了测量原理, 简要叙述了装置总体结构,介绍了测量装置各部分,给出了散射屏的散射特性,重点分析了光路布局、镜头焦距、光圈、景深、滤光片的参数选择,介绍了数据处理软件,给出了激光强度分布测量实验结果。结果表明：漫透射成像法测量激光强度时空分布是可行的,该装置测量强度分布分辨力高达5 mm;测量功率准确、可靠,测量不确定度小于6%,使用方便,实现了在小空间内对大光斑进行功率和强度分布的同时准确测量。     

Laser Doppler imaging through tissues phantoms by using self-mixing interferometry with a laser diode

Laser Doppler imaging has been widely used for the evaluation of cutaneous blood flow. We report on how the self-mixing interferometry configuration with a laser diode is explored for what is believed to be the first time to generate flow maps. The experiment was carried out by sensing the laser intensity power spectrum at each pixel as the laser was scanned over a model that mimics the properties of skin and circulating blood.     

Position sensor based on slit imaging

A position sensor based on slit imaging is proposed and its measurement principle is described.An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system.A magnified image of the detection double slit is formed on a bi-cell detector.The position of the imaging slit is obtained by detecting light intensity on two parts of the bi-cell detector.In experiments,the feasibility of the sensor was verified.The repeatability was less than 40 nm.     

Research on a flash imaging lidar based on a multiple-streak tube

A flash imaging lidar based on a multiple-streak tube is presented in this paper; a fiber remapping optics maps light from an area in the focal plane of an imaging lens to multiple rows of fibers on the streak tube’s photocathode. The lidar system contains a multiple-streak tube, laser, transmitting and receiving telescope, remapping optical fibers, and CCD to capture stripe images from the streak tube’s phosphor screen. Data processing yields 48 × 48-pixel intensity and range images for each laser pulse. An experiment to test the property of this lidar is carried out in the laboratory; the intensity images and range images are gained by image remapping, and the range sampling is 0.21 m. Field test imagery demonstrated the capability of the flash lidar system to image a building 705 m away.     

Superresolution vibrational imaging by simultaneous detection of Raman and hyper-Raman scattering

We have developed a superresolution vibrational imaging method by simultaneous detection of Raman and hyper-Raman scattering. Raman and hyper-Raman images obtained with the same laser spot carry independent information on the sample spatial distribution, owing to different signal dependence (linear in Raman and quadratic in hyper-Raman) on the incident light intensity. This information can be quantitatively analyzed to recover the incident light intensity distribution at the focal plane. A superresolution vibrational image is then derived by the constrained deconvolution of the images by the obtained incident light intensity distribution. This method has been applied to a TiO? nanostructure and the obtained superresolution image was compared with a scanning electron microscopy image. The spatial resolution achieved by the present method is evaluated to be 160 nm, which is more than twice better than the diffraction limited resolution.     

Measurement of micro weld joint position based on magneto-optical imaging

In a laser butt joint welding process,it is required that the laser beam focus should be controlled to follow the weld joint path accurately.Small focus wandering off the weld joint may result in insufficient penetration or unacceptable welds.Recognition of joint position offset,which describes the deviation between the laser beam focus and the weld joint,is important for adjusting the laser beam focus and obtaining high quality welds.A new method based on the magneto-optical(MO)imaging is applied to measure the micro weld joint whose gap is less than 0.2 mm.The weldments are excited by an external magnetic field,and an MO sensor based on principle of Faraday magneto effect is used to capture the weld joint images.A sequence of MO images which are tested under different magnetic field intensities and different weld joint widths are acquired.By analyzing the MO image characteristics and extracting the weld joint features,the influence of magnetic field intensity and weld joint width on the MO images and detection of weld joint position is observed and summarized.     

Acoustically modulated speckle imaging of biological tissues

A video laser speckle imaging technique yields images with contrast based on the mechanical properties of a tissue. Fluctuations of laser speckle patterns induced by acoustically driving the tissue at various frequencies in the 0-30-Hz range encode the mechanical strain of the tissue. At each acoustic frequency and within the camera acquisition time, each camera pixel integrates a temporally fluctuating speckle intensity whose variance encodes the mechanical strain in response to the acoustic modulation. The magnitude and the frequency dependence of this strain provide mechanical information about the tissue and are the contrast mechanism for images.     

一种改进激光偏振主动成像的建模及理论分析

提出一种改进激光偏振主动成像的实验方法,给出实验装置原理图,详细分析实验装置的成像原理。在分析目标Mueller矩阵测量方法的基础上,给出改进后激光偏振成像装置偏振度和强度的计算公式,从理论上证明了该方法的可行性。然后针对实验仪器的要求分析了实验装置存在的误差,以及Cassegrain望远镜对目标散射光的消偏现象。该方法与利用双旋转波片技术（DRRT）测量目标散射光的偏振度和强度相比可以降低对实验装置的精度要求,同时可以提高测量速度,不需要进行16次测量,只需1次就可以测量出目标散射光的偏振度和强度,进而得到偏振度和强度图像。     

Color imaging in photorefractive crystals

Color phase-conjugate imaging is demonstrated using a multi-colored laser beam. Speed of response, size of the image, clarity of the image, and the intensity of the image are investigated. Color images are stored and recalled without crosstalk between different colors.     

非线性介质对粒子场同轴全息成像的影响

 通过理论分析和实验验证,研究了非线性折射率介质对粒子场同轴全息成像的影响。利用粒子场同轴夫琅和费全息记录和光束在非线性介质中传输的波动方程,得出了光波的复振幅和强度分布。数值模拟了介质在线性和非线性时全息记录的情况,并进行了实验验证。结果表明：光波经非线性介质传输后,全息干板记录到粒子场的再现图像,这为高功率激光应用于全息照相提供参考,原因是高功率脉冲激光聚焦易击穿介质产生非线性传输。     

Fluorescence lifetime imaging with a low-repetition-rate passively mode-locked diode-pumped Nd:YVO4 oscillator

We report a wide-field fluorescence lifetime imaging microscope based on a low-repetition-rate (3.7-MHz) passively mode-locked diode-pumped laser source. This inexpensive and compact laser source operating in the visible and UV range can excite a wide range of fluorophores of biological interest. We demonstrate that the power of this laser source is highly sufficient for studying biological systems with low quantum yields (autofluorescence of tissues and stained living cells). The maximum measurable lifetime is also strongly increased with this laser source, as fluorescence intensity measurement can occur 250 ns after the excitation pulse.     

天基激光告警系统成像特征及信噪比研究

目标成像特征和信噪比是天基激光告警系统优化设计、目标检测及攻击事件判定的重要依据.在介绍告警系统结构的基础上,分析计算了攻击激光成像光斑的情况,并进行了实验验证,讨论了系统的背景光噪声环境,计算了入瞳处的背景光辐照度,推导了系统成像信噪比公式,并得到了攻击激光成像信噪比.结果表明:攻击激光在正入射情况下的理论光斑直径约...     

CO2激光外差接收的实时强度成像

利用国内的元器件建立了声光调制CO_2激光外差接收系统,并进行了实验室内静止目标的实时强度成像,成像距离3m,成像视场7°× 5°,像素128×98,4个颜色梯度显示像强度.     

Pulse-shape-free method for long-range three-dimensional active imaging with high linear accuracy

We present a three-dimensional (3D) imaging method employing linear increasing gain to encode flying time of photons into intensity information. This method obtains both the reflectivity and the depth of scene from only two two-dimensional (2D) images. High linear accuracy between the depth and the intensity information is independent of the laser pulse shape. We demonstrated <1 m linear depth accuracies with two different kinds of laser pulse shape and a 3D scene reconstruction with supperresolution depth mapping when the targets are 800-1100 m away.     

带宽对强光束非线性成像的抑制效应

 宽频带激光驱动器中光束的传输与常规的窄带系统有很大区别。数值分析了宽带激光的成像这一非线性传输现象,并与窄带激光的成像特性进行了比较,发现宽带激光的热像位置和窄带激光基本相同,但宽带激光的热像强度比窄带激光低很多,说明宽带激光能很好地抑制非线性成像的形成。此外,通过改变脉冲啁啾和脉冲宽度两种方式分别揭示了带宽对非线性成像和光束匀滑的影响,发现不同带宽情形下热像的位置基本相同,均处于共轭位置处;热像的光强和热像处光束的调制对比度随着啁啾值的增大而降低,随脉冲宽度的增大而增大。由于受到群速度色散效应的作用,带宽能够阻碍热像的形成,并提高光束的匀滑度。     

Application of the laser generated focused-Lamb wave for non-contact imaging of defects in plate

The laser generation method of focused-Lamb wave is expected to have high defect-detection ability with advantages of non-contact testing. In this method, the laser beam is illuminated on the surface of the object through an arrayed-arc slit, and then the energy of the generated Lamb wave is concentrated on the focus point of arc. This focusing effect enables the concentration of higher wave intensity on the focus with better S/N ratio of signal, and has better spatial resolution compared to the conventional line arrayed method. This paper describes a 2-D imaging system using this laser generated, focused-Lamb wave combined with its detection by the air-coupled transducer. This technique is fully non-contact so it can be easily applied for the automatic inspection. The effectiveness of the proposed method was verified by experiments on a 1-mm thick aluminum plate with artificial drill-hole defect with diameters of 1mm. The 2-D image of was constructed by scanning and the result showed that the location and size of defects were clearly detected.     

强激光场下原子超快动力学过程中的能量交换

利用三维经典系综模型,研究了整个系综两电子(Ar原子为例)从激光场吸收的能量对激光参数(波长、激光强度和椭偏率)的依赖关系.结果显示,当激光强度固定,波长增加时,整个系综两电子从激光场吸收的能量整体呈上升趋势,但不同强度下趋势略有差异.在较低强度时整个系综两电子从激光场吸收的能量对波长的依赖关系呈现持续平稳增加的趋势,在较高强度时呈现先缓慢减小再快速增大的趋势.对强度的依赖关系在不同波长时呈现两个有趣的交叉点.对椭偏率的依赖关系在较低强度时呈现先逐渐减小再缓慢增大的趋势;在中等强度时呈现一个“阶梯型”即先缓慢增大再逐渐减小最后缓慢增大;在更高强度时呈现先逐渐增大再逐渐减小的趋势.为了解释整个系综两电子从激光场吸收的能量对激光参数的依赖关系,把整个系综的动力学过程分为双电离、单电离、受挫单电离和受挫双电离4种通道.然后分析各个通道的特征及其如何主导整个系综两电子从激光场吸收的能量的变化趋势.分析结果表明,整个系综两电子从激光场吸收的能量对波长、激光强度和椭偏率的依赖均是由于某种通道主导整个系综两电子从激光场吸收的能量的结果.