Multi-Laser Beams Measuring System for High Precision Detection on Displacement of Wind Fields

A novel multi-laser beams measuring system （MLBM） for high precision detection on displacement of flow fields based on laser backscatter was designed and studied. MLBM has many advantages, such as simple structure, high stability, and no limitation of the monochromaticity of laser. By circumventing the strong influence of atmospheric backscattering on the high sensitivity of target echo detection, high precision detection on backscatter density of laser by signal processing was achieved. Furthermore, the signal densities of various distances were extracted by time sampling and precise frequency control of digital circuit. Finally, the MLBM system including devices integrated of emitting and reviving equipments and program was obtained. Detection experiments showed that our system has high precision and the measurement error could be controlled within 5% to 10%.

Digital Cross-Correlation Detection of Multi-Laser Beams Measuring System for Wind Field Detection

A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finite impulse response （FIR） digital filter. The processing of backscatter signals using single-pulse and three-pulse cross-correlation detection methods is depicted in detail. From calculation results, the multi-pulse cross-correlation detection could effectively improve signal-to-noise ratio （SNR）. Finally, both wind velocity and direction are determined by the peak-delay method based on the correlation function which shows high measuring precision and high SNR of the MLBM system with the assistance of the digital cross- correlation detection.

Laser guiding of cold molecules in a hollow optical fiber and continuous-wave cold molecular beam generation

A novel scheme for guiding arbitrary buffer-gas cooled neutral molecules in a hollow optical fiber （HOF） using a red-detuned HEll mode is proposed and analysed theoretically. We give the electromagnetic field distribution of the HEll mode in the HOF and calculate the optical potential of an 12 molecule, and study the molecule guiding mechanism using a classical Monte Carlo simulation. Using a 6 kW input laser, an S-shape HOF with a 2 cm curvature radius for both bends, and an input molecular beam with a transverse temperature of 0.5 K and longitudinal temperature of 5 K, we obtain a guiding efficiency of -0.126% for the scheme, and the transverse and longitudinal temperatures of the guided molecular beam are 1.9 mK and 0.5 K, respectively.

2-D localization system utilizing M-sequence encoded laser beam scanning

In this paper, as the active position measurement system, a novel method for a two-dimensional localization system using M-sequence signal is proposed. The feature of this system is to realize a position measurement only by scanning the encoded laser beams from fixing points to a measurement field, and by observing it. First, both the system configuration and encoding method were practically considered, and an order and an initial value of M-sequence signal were selected for encoding. This method is based on discrete angle measurement therefore the resolution has its own limitation. To overcome this limitation, analogue phase shift detecting method was introduced. System design was performed and applied to position measurement experiments. The experimental results show that the measurement error of the analogue method is 1/3 of that of the discrete method.

Numerical investigation of multi-beam laser heterodyne measurement with ultra-precision for linear expansion coefficient of metal based on oscillating mirror modulation

This paper proposes a novel method of multi-beam laser heterodyne measurement for metal linear expansion coefficient. Based on the Doppler effect and heterodyne technology, the information is loaded of length variation to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain many values of length variation caused by temperature variation after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, it can obtain length variation accurately, and eventually obtain the value of linear expansion coefficient of metal by the calculation. This novel method is used to simulate measurement for linear expansion coefficient of metal rod under different temperatures by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.4%.

Novel Method for Spatial Angle Measurement Based on Rotating Planar Laser Beams

Spatial angle measurement, especially the measurement of horizontal and vertical angle, is a basic method used for industrial large-scale coordinate measurement. As main equipments in use, both theodolites and laser trackers can provide very high accuracy for spatial angle measurement. However, their industrial applications are limited by low level of automation and poor parallelism. For the purpose of improving measurement efficiency, a lot of studies have been conducted and several alternative methods have been proposed. Unfortunately, all these means are either low precision or too expensive. In this paper, a novel method of spatial angle measurement based on two rotating planar laser beams is proposed and demonstrated. Photoelectric receivers placed on measured points are used to receive the rotating planner laser signals transmitted by laser transmitters. The scanning time intervals of laser planes were measured, and then measured point＇s horizontal/vertical angles can be calculated. Laser plane＇s angle parameters are utilized to establish the abstract geometric model of transmitter. Calculating formulas of receiver＇s horizontal/vertical angles have been derived. Measurement equations＇ solvability conditions and judgment method of imaginary solutions are also presented after analyzing. Proposed method for spatial angle measurement is experimentally verified through a platform consisting of one laser transmitter and one optical receiver. The transmitters used in new method are only responsible for providing rotating light plane signals carrying angle information. Receivers automatically measure scanning time of laser planes and upload data to the workstation to calculate horizontal angle and vertical angle. Simultaneous measurement of multiple receivers can be realized since there is no human intervention in measurement process .Spatial angle measurement result indicates that the repeatable accuracy of new method is better than 10＂. Proposed method can improve measurement＇s automation degree and speed while ensuring measurement accuracy.

Techniques trend analysis of propagating laser beam quality measurement

Different methods of measuring a propagating laser beam quality are summarized.The disadvantages in traditional way in measuring a laser beam quality is analyzed and the insufficiencies of the Shack-Hartmannin method which is commonly using wave front technique at present is pointed out.Finally,the transmission intensity equation based(TIE-based)measuring way in a laser beam quality evaluation and the corresponding advantages are discussed,which is believed to be a deve-l oping trend in laser beam evaluation.

STUDY ON THE OPTICAL FLAT PROFILE HIGH PRECISION MEASURING TECHNOLOGY IN THE METHOD OF LASER DATUM

The physical datum method that uses the laser beam as the physical datum is proposed.A high accuracy of the straight movement on the line above 0.01 μm/100 mm is achieved through applying the method of the closed loop feedback control that uses the laser beam as the datum.The measuring accuracy above 0.05 μm is obtained by applying the self making electric eddy displacement sensor to detect the geometric accuracy of the optical flat.It proves that the laser beam datum method can achieve the high accurcy of the straight movement and has the huge advantage.

Beam guiding system geometric arrangement in the target area of high-power laser drivers

With the increasing number of laser beams, the main difficulty in arranging beam guiding systems(BGSs) involves determining the corresponding relationships between the output and input ports to realize the identified light path length of all beams. Given the basic constraints of geometric arrangement, a BGS model is established, and a base-line algorithm is proposed to address the difficulty mentioned above. Boundary conditions of target area and target chamber are discussed to increase the number of laser beams, and a maximum value exists for a specific target area. Finally, the compatibility of a cylindrical hohlraum target chamber with a spherical hohlraum is analyzed, and a moveable final optics assembly is proposed to execute the switch between the two different targets.

Proton Acceleration with Nano-Scale Micro-Structured Target by Circularly Polarized Laser Pulse

Two dimensional particle-in-cell simulations are taken to study the interaction of a circularly polarized laser pulse with a nano-scale micro-structured target. The protons which are doped in the rear side of the target experience the electrostatic fields caused by both the radiation pressure driven shock and the target normal sheath at the rear side of the target. A quasimonoenergetic proton bunch with central energy of about 11MeV and energy spread of ＆#8710; ε/ε about 0.18 is achieved by using a 3.45×1019 W/cm2, 66fs laser pulse. A comparison with the case of linearly polarized laser pulse and the same target condition is considered.

Faraday-rotation self-interference method for electron beam duration measurement in the laser wakefield accelerator

Real-time single-shot measurement of the femtosecond electron beam duration in laser wakefield accelerators is discussed for both experimental design and theoretical analysis that combines polarimetry and interferometry.The probe pulse polarization is rotated by the azimuthal magnetic field of the electron beam and then introduced into a Michelson-type interferometer for self-interference. The electron beam duration is obtained from the region size of the interference fringes, which is independent of the pulse width of the probe laser. Using a larger magnification system or incident angle, the measurement resolution can be less than 1 fs.

Improvement of Beam Energy Measurement System for BES-III

The beam energy measurement system is significant and profit for both BES-III detector and BEPC-II accelerator. The detection of the high energy scattering photons is realized by virtue of the Compton backscattering principle. Many advanced techniques and precise instruments are employed to acquire the highly accurate measurement of positron/electron beam energy. During five years’ running period, in order to satisfy the requirement of data taking and enhance the capacity of measurement itself, the upgradation of system is continued, which involves the components reformation of laser and optics subsystem, replacement of view-port of the laser to vacuum insertion subsystem, the usage of electric cooling system for high purity germanium detector, and the refinement of data acquisition and processing subsystem. The upgrading of system guarantees the smooth and effective measuring of beam energy at BEPC-II and accommodates the accurate offline energy values for further physics analysis at BES-III.

Determination of the focused beam waist of lasers with weak measurements

In this Letter, a method for detecting the focused beam waist of lasers is proposed by using weak measurements based on the so-called weak-value amplification. We establish a propagation model to describe the quantitative relation between the beam waist and the amplified shift of the spin Hall effect of light(SHEL), which is sensitive to the variation of the beam waist. We experimentally measure the amplified shift corresponding to a different beam waist and the experimental data agrees well with theoretical calculation. These results confirm the rationality and feasibility of our method.

Precise measurement of the micron-scale spot of ultrashort laser pulse based on film scanning

A novel and precise micron-scale nanosecond laser spot measurement based on film-scanning method is presented. The method can be used to measure the spot size, beam profile, and intensity distribution of the pulse. The central spot radius of the pulsed Bessel beams with pulse width of 25 ns is measured to be 94.86 ± 5 μm in our experiment through the analysis of the digital image by film scanning, and the result is consistent with the theoretical value of 92.33 μm. Compared with charge-coupled device/complementary metal oxide semiconductor （CCD/CMOS） laser beam profilers, the film-scanning method shows higher measurement accuracy, single shot ultrashort pulse measurable, larger measurable size, and wider measurable wavelength range.

空化现象对水导激光微水束稳定性的影响研究

为了探寻空化现象对水导激光微水束稳定性影响,利用计算流体动力学的方法,分别在不考虑空化和考虑空化的情况下,对从典型喷嘴出射的水射流进行了数值模拟分析,研究了空化现象的产生机理及对微水束稳定性的影响。结果表明,在入口直径为0.1 mm、圆柱段长径比为1、上边缘锐利的喷嘴结构下,随着入口压力从0.2 MPa增大到16 MPa,水射流与喷嘴壁面分离后再次附着的长度逐渐增大,并且空化会导致该长度延长;在入口压力小于6 MPa的情况下,不考虑空化的水射流在稳定后会贴着喷嘴壁面流下,而添加空化模型使得水束形成翻转流。该研究对设计满足水导激光工艺的喷嘴结构有着重要的参考价值。

Stochastic resonance for signal-modulated pump noise in a single-mode laser

By adopting the gain-noise model of the single-mode laser in which with bias and periodical signals serve as inputs. combining with the effect of coloured pump） noise, we use the linear approximation method to calculate the power spectrum and signal-to-noise ratio （SNR） of the laser intensity under the condition of pump noise and quantum noise cross-related in the form of δ function. It is found that with the change of pump noise correlation time. both SNR and the output power will occur stochastic resonance （SR）. If the bias signal α is very small, changing the intensities of pump noise and quantum noise respectively does not lead to the appearance of SR in the SNR： while α increases to a certain number, SR appears.

高能激光短距离传输光束质量测量仿真与实验研究

准确测量光束质量对于高能激光系统性能的评估至关重要,相比传统的远距离传输测量后再修正的方法,短距离传输后的光束质量更接近激光系统出口处的真实情况。建立激光短距离传输模型,采用多层相位屏法,分析空气湍流等因素对激光远场光斑形态和光束质量的影响。结果表明,在20 m的较短传输路径上,风速、空气相对湿度、功率等影响热晕效应的因素对光束质量影响较小,常规条件范围内,光束质量因子β值劣化不超过15%,而空气湍流效应对高能激光光束质量的影响较明显,随着空气湍流强度C_(n)^(2)由1×10^(-18)m^(-2/3)增大到1×10^(-12)m^(-2/3),β值从1.0848增大至8.9933;湍流强度对不同口径激光光束的光束质量影响也不尽相同,口径越大,受湍流强度影响越大。文中搭建实物光路,使用700 mm口径平行光管进行验证,在C_(n)^(2)<1×10^(-14)m^(-2/3)的情况下,测得2.63,与模拟结果相符,实验中还发现,可以通过搅散空气的方法来减小湍流强度。实验结果表明:将空气湍流强度控制在1×10^(-14)m^(-2/3)以下,光束质量因子不小于3的高能激光系统光束质量测量偏差小于5%,为大口径激光系统出口光束质量测量提供一种解决方案。

基于光束分析的高功率激光切割头光路优化

20mm碳钢亮面是万瓦切割能力验证的典型板材,采用超音速单层1.2孔径喷嘴,焦点在+12.5mm左右的离焦量,可以产生较好的切割效果,而此时激光切割头普遍存在喷嘴发烫,无法长期稳定切割的问题;通过对激光头进行光学软件模拟及光束分析仪实际测试,结果表明良好的切割效果不仅取决于聚焦光路长度,同时还与光路总长有密切关系;不同切割头内冷却及吸光装置不同,可能是光路相同情况下影响出射光束的主要原因。

基于三维激光扫描技术的液压支架顶梁变形量检测技术研究

液压支架的顶梁是支架的主要承载部件,在液压支架型式检验中,顶梁变形量是否超标是判定产品合格与否的主要技术指标之一。国内外液压支架进行定型检验时均需要测量顶梁变形量,以验证其顶梁结构强度。为解决液压支架顶梁变形量手工测量效率低、重复精度低等问题,基于三维激光扫描技术,提出了液压支架顶梁变形量检测的一种新方法,介绍了技术设计方案、成果分析以及测量结果验证,实现了液压支架顶梁变形量高精度、广适应性的检测,检测精度最高0.02 mm/m,能满足液压支架检验需求,还可以为液压支架检验及设计提供数据支持。

基于数学形态学的小孔径高斯光束光斑半径测量方法

为减小现有的激光光束光斑半径测量方法的测量误差,设计基于数学形态学的小孔径高斯光束光斑半径测量方法。对小孔径光斑几何特征进行划分,计算探测误差,获取光斑能量在探测器光敏面上的均匀分布函数,得到质心点到光斑轮廓点的距离。建立高斯光束光斑轮廓模型,获取位置轮廓的灵敏度,并计算其在某光斑点位的能量值,通过质心点的误差函数,得到光斑点的轮廓函数。基于数学形态学设计光斑半径测量方法,计算不同方向与尺度元素在对角线上的梯度幅值,得到激光光束光斑的半径长度。分析光照强度与发射角对测量精度的影响,实验结果显示:在该激光光束下,光照强度为80且发射角度为1.8时,测量误差最小。对比4种测量方法的测量误差,由数据可知,数学形态学的测量方法误差最小,可见该方法优于其他测量方法。