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.

A Method of Insulator’s NSDD Measurement and Its Device Based on Laser Transmission Principle

Accuracy measurement of the Non-soluble Deposit Density (NSDD) on the insulator surface is very important for the transmission line anti-pollution flashover works. A method to measure the NSDD on double sheds porcelain insulator surface based on laser transmission principle is proposed in this paper. Laser unit and luminous intensity sensor are installed between the up and down surface of the double sheds porcelain insulators, two glass tablets are put between the double sheds. The contamination on the glass tablets will influence the luminous intensity that reaches the intensity sensor. The luminous signal is changed to electrical signal, and the insulator’s NSDD could be obtained based on the difference of luminous intensity. The device can be used in online monitoring of the insulator's NSDD condition on the insulator surface.

Energy and flux measurements of laser-induced silver plasma ions by using Faraday cup

Silver(Ag)plasma has been generated by employing Nd:YAG laser(532 nm,6 ns)laser irradiation.The energy and flux of ions have been evaluated by using Faraday cup(FC)using time of flight(TOF)measurements.The dual peak signals of fast and slow Ag plasma ions have been identified.Both energy and flux of fast and slow ions tend to increase with increasing irradiance from 7 GW cm-2 to 17.9 GW cm-2 at all distances of FC from the target surface.Similarly a decreasing trend of energies and flux of ions has been observed with increasing distance of FC from the target.The maximum value of flux of the fast component is21.2×10^(10) cm^(-2),whereas for slow ions the maximum energy and flux values are 8.8 keV,8.2×10^(10) cm^(-2) respectively.For the analysis of plume expansion dynamics,the angular distribution of ion flux measurement has also been performed.The overall analysis of both spatial and angular distributions of Ag ions revealed that the maximum flux of Ag plasma ions has been observed at an optimal angle of~15°.In order to confirm the ion acceleration by ambipolar field,the self-generated electric field(SGEF)measurements have also been performed by electric probe;these SGEF measurements tend to increase by increasing laser irradiance.The maximum value of 232 V m^(-1) has been obtained at a maximum laser irradiance of 17.9 GW cm^(-2).

A Self-Mixing Microvibration Measurement System of a π-Phase Shifted DFB Fiber Laser

Recently, with the rapid development of precision machining, microvibration measurement is required for the manufacturing and installation of parts and components. In this paper, a self-mixing microvibration measurement system of a π-phase shifted Distributed feedback (DFB) fiber laser is introduced. An all-fiberized configuration Er3+-Yb3+ co-doped DFB fiber laser was used as light source, in which an active π-phase shifted fiber Bragg grating (FBG) was wrote on Er3+-Yb3+ co-doped fiber. Using this, it can easily get a single-mode lasing with narrow linewidth. Experimental results demonstrate that the amplitude of vibration can be achieved down to λ/5 without any modulation parts while utilizing the reflecting mirror. It is in good agreement with the theoretical analysis and very helpful in proving sensitivity and stability of the measurement system. In addition, remote vibration measurement with a distance of 20 km is also realized with this system.

Light intensity distribution of a new type of contact laser scalpel

The emergent light distribution of a new type of contact laser scalpel is measured in three different states using a light sensor. The relationship between the angle and the light intensity is analyzed. The results show that the strongest light is emitted from two sides and the front of the scalpel. The light from the front mainly plays a role of cutting. The light from two sides contributes to stanch the wound so as to remain a clear visual field during the surgery. It also helps to increase the cutting efficiency.

Numerical Study of the Threshold Intensity Dependence on Wavelength in Laser Spark Ignition of Molecular Hydrogen Combustion

A numerical investigation of laser wavelength dependence on the threshold intensity of spark ignition in molecular hydrogen over a wide pressure range is presented. A modified electron cascade model (Gamal et al., 1993) is applied under the experimental conditions that carried out by Phuoc (2000) to determine the threshold intensity dependence on gas pressure for spark ignition in hydrogen combustion using two laser wavelengths namely;1064 nm and 532 nm. The model involves the solution of the time dependent Boltzmann equation for the electron energy distribution function (EEDF) and a set of rate equations that describe the change of the formed excited molecules population. The model takes into account most of the physical processes that expected to occur in the interaction region. The results showed good agreement between the calculated thresholds for spark ignition and those measured ones for both wavelengths, where the threshold intensities corresponding to the short wavelength (532 nm) are found to be higher than those calculated for the longer one (1064 nm). This result indicates the depletion of the high density of low energy electrons generated through multi-photon ionization at the short wavelength via electron diffusion and vibrational excitation. The study of the EEDF and its parameters (viz, the temporal evolution of: the electron density, ionization rate electron mean energy, …) revealed the important role played by each physical process to the spark ignition as a function of both laser wavelength and gas pressure. More over the study of the time variation of the EEDF explains the characteristics of the ignited spark at the two wavelengths for the tested pressure values.

Ultrafast photoionization of ions and molecules by orthogonally polarized intense laser pulses: Effects of the time delay

We present the photoelectron momentum distributions(PMDs) and the photoelectron angular distributions(PADs) of He+ ions, aligned H2+ molecules and N2 molecules by intense orthogonally polarized laser pulses. Simulations are performed by numerically solving the corresponding two-dimensional time-dependent Schr?dinger equations(TDSEs) within the single-electron approximation frame. Photoelectron momentum distributions and photoelectron angular distributions present different patterns with the time delays Td, illustrating the dependences of the PMDs and PADs on the time delays by orthogonally polarized laser pulses. The evolution of the electron wavepackets can be employed to describe the intensity of the PADs from the TDSE simulations for N2 molecules.

Internal and near-surface fields for a chiral sphere under arbitrary laser beam illumination

A general scheme for the investigation of scattering by a chiral sphere under arbitrary monochromatic laser beam illumination is presented. The scattered and internal fields are expanded by using appropriate spherical vector wave functions, and their expansion coefficients are determined by the boundary conditions and the projection method. Targeting multiple incidence forms such as Gaussian beam, Hermite–Gaussian beam, doughnut mode beam and zero-order Bessel beam, the influence and propagation of near-surface intensity field for a chiral sphere are analyzed. These properties are very important for studying the properties of chiral media, and for manipulating the optical tweezers and super-resolution imaging of particles.

The intensity distribution and thermal stability of InnoSlab laser

Partially end-pumped slab laser is an innovative solid state laser, namely InnoSlab. Combining the hybrid resonator with partially end-pumping, the output power can be scaled with high beam quality. In this paper, the output intensity distributions are simulated by coordinate transformation fast Fourier transform (FFT) algorithm, comparing the thermal lens influence. As the simulated curves showed, the output mode is still good when the thermal lens effect is strong, indicating the good thermal stability of InnoSlab laser. Such a new kind of laser can be designed and optimized on the base of this simulation.

THE MEASUREMENT OF INTENSE PULSED CURRENT IN RAMAN FREE ELECTRON LASER

The Free Electron Laser(FEL), for its ideal optical medium that is the flee electron which in vacuum has no bound energy level, has demonstrated its potential in tunable frequency and ultra-high power application fields.After basic mechanisms of FEL are verified, in research enthusiasm has naturally been transferred from theory to experiment, from proving to how to consummate the present

The momentum distributions of triatomic molecular ion H_(3)^(2+) by intense laser pulses

We investigate theoretically the photoionization of triatomic molecular ion H_(3)^(2+) by numerically solving the two-dimensional time-dependent Schrödinger equations under Bohn-Oppenheimer approximation.The results show that the photoelectron momentum distributions(PMDs)of H_(3)^(2+) with different initial states are strongly dependent on the laser ellipticities and molecular orbital symmetry,and the PMDs of degenerate electronic states E^(±)are mirror images.Also,for degenerate electronic states E^(±),vortex structures appear in the PMDs by the counter-rotating circularly polarized laser pulses as the time delay between the two pulses increases,which can be explained by multicenter ionization and ultrafast photoionization model.

All-optical clock recovery for 40 Gbaud NRZ-QPSK signals using amplified feedback DFB laser diode

An all-optical clock recovery scheme based on monolithic amplified feedback DFB laser （AFL） diode is proposed for nonreturn-to-zero （NRZ） quadrature phase shift keying （QPSK） format signals. By using a preprocessing stage, clock recovery （CR） is successfully demonstrated for 40-Gbaud NRZ-QPSK signals based on this scheme. The dependence of the timing jitter of the recovered clock on the optical power of the injected signal is investigated. A minimum timing jitter of 362.8 fs （integrated within a frequency range from 10 Hz to 10 MHz） is obtained.

Cascaded Random Raman Fiber Laser With Low RIN and Wide Wavelength Tunability

Cascaded random Raman fiber lasers(CRRFLs)have been used as a new platform for designing high power and wavelength-agile laser sources.Recently,CRRFL pumped by ytterbium-doped random fiber laser(YRFL)has shown both high power output and low relative intensity noise(RIN).Here,by using a wavelength-and bandwidth-tunable point reflector in YRFL,we experimentally investigate the impacts of YRFL on the spectral and RIN properties of the CRRFL.We verify that the bandwidth of the point reflector in YRFL determines the bandwidth and temporal stability of YRFL.It is found that with an increase in the bandwidth of the point reflector in YRFL from 0.2 nm to 1.4 nm,CRRFL with higher spectral purity and lower RIN can be achieved due to better temporal stability of YRFL pump.By broadening the point reflector’s bandwidth to 1.4 nm,the lasing power,spectral purity,and RIN of the 4th-order random lasing at 1349 nm can reach 3.03 W,96.34%,and–115.19 dB/Hz,respectively.For comparison,the spectral purity and RIN of the 4th-order random lasing with the point reflector’s bandwidth of 0.2 nm are only 91.20%and–107.99 dB/Hz,respectively.Also,we realize a wavelength widely tunable CRRFL pumped by a wavelength-tunable YRFL.This work provides a new platform for the development of ideal distributed Raman amplification pump sources based on CRRFLs with both good temporal stability and wide wavelength tunability,which is of great importance in applications of optical fiber communication and distributed sensing.

Optical diagnostics of laser beam quality for the Beijing Free Electron Laser (BFEL)

FEL has some advantages: its wavelength is tunable in a wide range; light beam quality is good and it has an ultra-short pulse construction. So it is applied in the fields of material, nonlinear optics and biomedicine. BFEL operated successfully, making China become a country having infrared FEL by using RF linear accelerator following America, Netherlands and France. A saturation oscillation was made at the end of

折反式激光粒度测量方法

激光粒度仪因其快速、非接触等优点被广泛应用于各领域的粒度分布测量,但颗粒散射光的角分布与粒度大小关系复杂。为了获得不同粒度下的相对精度一致,通常会造成粒度分布测量范围小、无法满足宽分布粒度测量要求等问题。根据Mie散射近似的菲涅尔原理,提出采用折反式光路,将颗粒散射信号由分光镜分成两束,经两组组合式镜头和2个光电探测器分别采集透射和反射的散射信号,信号组合后经反演得到颗粒粒度分布,从而提高了可测粒度范围。采用两种标准粒子及其混合物进行了实验,结果表明,单种标准粒子测量结果的体积中位径D50的测量相对误差都不大于7.9%;对混合粒子也能够得到正确的峰值分布。

基于激光雷达数据的塔里木河下游胡杨种群空间分布格局和种内竞争关系

【目的】分析胡杨种群在干旱区不同地下水埋深梯度下的空间分布格局及种内竞争强度变化,探究种群空间结构对干旱环境的响应特征。【方法】在塔里木河下游3个断面处离河道1 000 m的范围内等距离布设15个50 m×50 m天然胡杨林样地,利用地面激光雷达(TLS)获取树木三维结构数据,并通过聚集指数(R)、丛生指数(I)、点格局函数g(r)等空间分布指标以及竞争指数(CI),分析空间分布格局和种内竞争强度。【结果】1)R和I指数表明,在下游不同地下水埋深梯度下,胡杨种群空间分布格局整体上呈聚集分布。2)各样地内在0~25 m半径r距离获取的g(r)函数值分析表明,大部分样地胡杨在r<5 m距离内基本呈现聚集分布格局,在r>5 m距离呈随机分布格局。随着地下水埋深增加,树木聚集分布的距离r会缩小。3)点格局函数g_(12)(r)结果表明,不同龄级胡杨树分布格局存在差异,中龄树主要呈聚集分布,其他龄级树呈随机分布;中龄树与幼龄树、成熟树之间存在正关联性,表现出相互促进关系,而其他龄级树木之间未呈现显著关联性。4)平均CI指数随离河道距离增大呈递减趋势,单木CI随胸径增大逐渐递减。【结论】塔里木河下游胡杨种群在小尺度上呈聚集分布格局,随着尺度的增加主要呈现随机分布特征。随离河道距离增大和地下水位逐步降低,导致树木密度降低和种内平均竞争强度变弱,树木呈衰退趋势。

激光衍射法测定西格列他钠粒径分布

目的建立西格列他钠的粒径分布测定方法,为药物粒径测定的方法开发和质量控制提供参考。方法采用MALVERN Mastersizer 3000激光衍射粒度仪和AEROS干法进样器建立西格列他钠的粒径分布方法。背景测量持续时间7 s;样品测量持续时间7 s;遮光度0.5%~5%;样品分散气压0.4 MPa;进样速度60%;文丘里管类型为高能文丘里管;料斗间隙2.5 mm。结果3批样品粒径分布特征值d(0.1)在1.02~1.17μm,d(0.5)在5.94~6.69μm,d(0.9)在20.70~22.40μm,平均标准偏差(RSD)均小于1%。结论建立了西格列他钠的粒度测定方法,可为其他易引湿药物的干法粒径测定方法开发提供参考。

光加热光纤光栅阵列液位测量方法研究

安全可靠的液位测量是现代工业领域的重要技术需求之一,提出一种基于光加热光纤光栅阵列的液位测量方法,即利用泵浦光加热掺钴光纤,控制温度场,利用光栅阵列测量温度场分布,由于气液导热性能的差别,气液界面处温度突变,从而确定液位。实验中,将掺钴光纤与密集光栅阵列紧密固定在一起,将1.5 W的泵浦光输入衰减系数分别为0.71 dB/cm和0.28 dB/cm的掺钴光纤中,沿着光传播的方向,温度变化均呈指数函数衰减。液位测量的精度与范围由主要取决于泵浦光功率、掺钴光纤吸收系数,经对比最终选定0.28 dB/cm的掺钴光纤作为液位实验的加热光纤。实验测量了不同液位下的温度场分布,证明了利用测量温度分布来测量液位的可行性,液位变化范围0~88 mm以内的误差为2 mm。所提出的传感系统结构简单,成本低廉,在液位测量方面具有潜在的应用价值。

全风化花岗岩路堑边坡降雨侵蚀时空分布特征测试与评估

为了测试及评估全风化花岗岩路堑边坡降雨侵蚀时空分布特征,选取在建云南墨临高速公路某全风化花岗岩路堑边坡某段开展现场测试。首先结合三维激光扫描测试及电测量技术,获取边坡坡面形态特征参数及边坡电阻率剖面;然后引入高斯分布模型及分位数图示法实现边坡材料属性定义,通过电阻率差异映射边坡侵蚀状态。结果表明:边坡底部及坡中部(y=0~40 m)区域呈现大面积侵蚀特征,在各级边坡平台处则呈现多点集中高侵蚀特征,侵蚀影响深度达5 m左右;随着植被防护等措施的施加,大面积侵蚀特征变为多点集中侵蚀特征,评估结果与坡面形态信息具有较好的一致性。该研究成果对于该边坡降雨侵蚀灾害防治具有重要的实际意义,并对同类研究具有借鉴作用。

激光超声时频参数对裂纹试件的温度检测

为了实现对高温工作环境下含表面裂纹试件的温度测量,提出了利用激光超声瑞利波的时、频参数实现表面裂纹试件温度测量的新思路。采用稳态解作为瞬态初始值的温度加载方法,建立了293.15~743.15 K温度范围内结构钢的表面裂纹试件模型,分析了激光超声瑞利波与表面裂纹的相互作用。在时域上,利用瑞利反射、透射波的归一化峰值来定义反射率、透射率这两个时域参数,得出反射率和透射率都与温度成线性增长关系,反射率和透射率随温度的变化率分别为1.45×10^(-3)dB·K^(-1)和2.3×10^(-3)dB·K^(-1);在频域上,提出了瑞利波的小波时频分析(TFA)分布下超声能量强度的特征极值点关系法,得出在特征频率为2.4 MHz时,能量强度的特征极值随温度的线性增长率为2.56×10^(-4)dB·K^(-1);实验分析证明了仿真结果的可行性。时、频域的研究结果结合实验分析表明,利用时、频参数与温度的线性关系和变化率,可实现表面含裂纹的试件的温度测量表征。