Investigation of positioning algorithm and method for increasing the linear measurement range for four-quadrant detector

The paper studied the relationship between the light spot position and the output voltage in the case of laser spot which is in the four-quadrant (4Q) detector whose shape is circle or elliptic, energy distribution uniform or Gaussian. The study is based on add–subtract algorithm, diagonal algorithm and difference over sum (Δ/∑) algorithm. By using methods of polynomial fitting it can get a simple polynomial expression to enhance measuring speed and the simulation error is given. A method of using Binary Optics Elements (BOE) to shape the laser beam in the 4Q detector to square light spot with uniform intensity distribution is proposed to expand linear measurement range. The simulation result is verified for a circular spot with Gaussian energy distribution.     

Measurement of a broad range of Gaussian laser beam diameters using various periodic and aperiodic rulings

A novel analytical approach is proposed for an accurate estimation of a broad range of Gaussian laser beam diameters. The new approach, based on the Fourier transform and the convolution operations, is used to study the performance of most recently proposed periodic and aperiodic rulings. Further, for applications that require extremely small beam diameter measurements, a new Ronchi-like ruling is proposed; while for applications requiring large beam diameters measurements, various aperiodic non-Ronchi rulings are proposed. Furthermore, for spot-size measurement applications, which range from very small to very large beam diameters, a new single aperiodic exponential ruling is proposed. This new ruling eliminates the necessity of using a large number of rulings for measuring a broad range of beam diameters.     

Effective Rayleigh range of Gaussian array beams propagating through atmospheric turbulence

The analytical expressions for the effective Rayleigh range z_R of Gaussian array beams in turbulence for both coherent and incoherent combinations are derived. It is shown that z_R of Gaussian array beams propagating through atmospheric turbulence depends on the strength of turbulence, the array beam parameters and the type of beam combination. For the coherent combination z_R decreases due to turbulence. However, for the incoherent combination there exists a maximum of z_R as the strength of turbulence varies. The z_R of coherently combined Gaussian array beams is larger than that of incoherently combined Gaussian array beams, but for the coherent combination case z_R is more sensitive to turbulence than that for the incoherent combination case. The larger the beam number is, the longer z_R is, and the more z_R is affected by turbulence. For the coherent combination z_R is not monotonic versus the relative beam separation distance, and the effect of turbulence on z_R is appreciable within a certain range of the relative beam separation distance.     

Flattop beam illumination for 3D imaging ladar with simple optical devices in the wide distance range

We have developed an illumination optical system for 3D imaging ladar (laser detection and ranging) which forms flattop beam shape by transformation of the Gaussian beam in the wide distance range. The illumination is achieved by beam division and recombination using a prism and a negative powered lens. The optimum condition of the transformation by the optical system is derived. It is confirmed that the flattop distribution can be formed in the wide range of the propagation distance from 1 to 1000 m. The experimental result with the prototype is in good agreement with the calculation result.     

激光测距机发射光学系统透射特性研究

为分析激光测距机发射光学系统透射特性对测距性能的影响,利用光线追迹公式和部分偏振光理论,得出了激光测距机发射光学系统透射率的定量解析式。针对发射光学系统特例,定量分析了其透射率与入射激光束偏振参量和几何光学参量间的关系。结果表明：随着入射角增加,激光束偏振参量对发射光学系统透射特性将产生较明显影响,当激光器发射的激光脉冲是随机的部分偏振光时将引起测距机发射激光脉冲能量的随机变化。     

Free-spectral range tunable Fabry-Perot filter with superimposed fiber Bragg gratings

A novel free-spectral range (FSR) tunable Fabry-Perot filter (FPF) with two superimposed fiber Bragg gratings (SFBGs) is proposed and experimentally demonstrated. The SFBGs, initially uniform in period with slightly different Bragg wavelengths, were glued onto the lateral surface of a specially-designed cantilever beam and linearly chirped by beam bending-induced strain gradient. As a result, their reflection bands overlap and a grating-based FPF with a tunable FSR is formed. A continuously tunable FSR of 0.1-0.5 nm has been achieved in the experiment.     

Resolution enhancement with improved range Doppler algorithm in high numerical aperture OCT

The improved range Doppler algorithm is proposed to abate the trade-off between resolutions and depth of focus in spectral domain optical coherence tomography.By considering the finite beam width and the shape of the wavefronts produced by the Gaussian beam,a physical diffraction model is presented to simulate the light propagation process in the sample.The two-dimensional processing of the spectrum data is decomposed into two one-dimensional processings of Stolt transform and matched filter.Experimental results show that image reconstruction can be achieved.The transverse and axial resolutions are both improved significantly,especially in the out-of-focus range,and the resolutions are almost equivalent throughout the entire region of interest.     

CCD系统线性动态范围的标定

 提出了一种标定CCD图像采集系统动态范围的实用方法。利用尖劈形成一列光强逐级衰减的标定光源,结合插值法给出CAS-512A CCD系统的线性动态范围。可用于强激光领域中CAS-512A CCD图像采集系统的实用线性动态范围的标定。     

Fast Gaussian wavepacket transforms and Gaussian beams for the Schrödinger equation

This paper introduces a wavepacket-transform-based Gaussian beam method for solving the Schrödinger equation. We focus on addressing two computational issues of the Gaussian beam method: how to generate a Gaussian beam representation for general initial conditions and how to perform long time propagation for any finite period of time. To address the first question, we introduce fast Gaussian wavepacket transforms and develop on top of them an efficient initialization algorithm for general initial conditions. Based on this new initialization algorithm, we address the second question by reinitializing the beam representation when the beams become too wide. Numerical examples in one, two, and three dimensions demonstrate the efficiency and accuracy of the proposed algorithms. The methodology can be readily generalized to deal with other semi-classical quantum mechanical problems.     

A spectral interferometric method to measure thickness with large range

We present a spectral interferometric method to measure the thickness of an optical plate or a film with a single layer. The system is based on the Michelson interferometer configuration, and the spectral interference signal of a broadband light source is recorded by a spectrometer. The optical path difference (OPD) between two interfering beams can be obtained by Fourier transform from the spectral interferogram. Gaussian fitting is used to find the exact peak of fringe to enhance the precision of the measurements. When the sample is inserted into the sample beam, the film’s thickness can be calculated by comparing the change of OPD, provided that the sample group refractive index is known. Only a single measurement is needed to determine a film’s thickness after the initial OPD of the system is calibrated. As no moving parts are required, the system has good stability. In particular, a large range of thicknesses, from micrometers up to several millimeters, can be measured. Such a large range is valuable for optical measurements. For demonstration, we measured the thicknesses of preservative film, cover glass and carrier glass, which were 9.6 ± 0.55, 156.1 ± 0.75, 1008.44 ± 0.96 μm, respectively.     

Analysis of detectable range of multiple-slit streak tube imaging lidar

Multiple-slit streak tube imaging lidar is a promising flash imaging system. Its detectable range, affected by the detection of the unit sensitivity, operating mode, and visibility, are critical factors for the system design and applications. In order to discuss the lidar range measurement performance, a lidar equation based on the Lambert law is analyzed, and the relationship between the lidar detectable range and the emission power is simulated at different levels of visibility; the result shows that the detectable range of lidar developed in our laboratory reaches 2,500 m for a 23 km visibility. Outfield experiments were carried out to evaluate the system performance; a clear stripe image for a target located 1386 m away was gained under the condition of 15 km visibility. Finally, parameters that affect the lidar detectable range are discussed, and relevant methods to improve the lidar performance are proposed.     

单水听器波导不变量被动测距

本文主要讨论利用声场干涉现象由单水听器被动测距的可行性及测距性能,为此提出了单水听器波导不变量被动测距方法,通过提取LOFAR图上干涉条纹、使用简正波模型计算波导不变量、频域相关法估计相对速度,最后依据干涉条纹方程得到声源距离估计量。数值仿真和海上实验结果验证了单水听器被动测距的可行性,并具备一定测距性能,在3 dB信噪比环境中,对于7 km处的运动声源,平均测距误差小于5%。本文方法具有设备简单、易于推广至阵列信号处理等特点,为声纳信号处理环境宽容性的提高及环境适配声纳的设计开拓了思路。     

Formation of expanded smooth quasi-Bessel beam range due to the transformation of the Gaussian beam in absorbing axicon

The quasi-Bessel beam range produced by an absorbing axicon is investigated. It is shown that when an incident Gaussian beam is used, the absorbing axicon stretches (with respect to transparent axicon case) the uniform on-axis light intensity distribution length, as well as expanding the quasi-Bessel beam range. In addition, the peak of axial light distribution is shifted from the axicon tip. As a result any spatial modulation formed due to the bluntness of the tip is reduced close to the on-axis intensity peak, which becomes more smooth and uniform.     

计算机制全息图改造激光波面和模式

以变换椭圆高斯光束为圆对称高斯光束为例,本文给出了用计算机制全息图作为变换元件改造激光波面和模式的理论和方法.推导出产生计算机制全息图的数学方程.制作出计算机制全息图,并得出了实验结果.     

高斯光束在对数型非线性介质中自诱导效应

从标量Helmholtz方程出发,推导了对数饱和非线性介质中光场满足的非线性Schr dinger方程(NLSE)。通过与梯度折射率下的光场满足的方程比较,发现高斯光束在对数型饱和非线性介质中可自诱导梯度折射率。利用数值计算,详细地讨论了自诱导梯度折射率对高斯光束传输特性的影响。发现高斯光束在其自诱导的梯度折射率的影响下,呈振荡形式的准稳定的传输。光束注入介质中的初始状态,直接影响着光束的振荡形式(先发散还是先聚焦)、振荡深度(幅度)、振荡周期。得到高斯光束形成孤子的条件,以及若使高斯光束在对数饱和非线性介质中保持小损耗、高稳定的传输,应该使光束在阈值(孤子条件)附近注入介质的结论。     

The backward phase flow and FBI-transform-based Eulerian Gaussian beams for the Schrödinger equation

We propose the backward phase flow method to implement the Fourier–Bros–Iagolnitzer (FBI)-transform-based Eulerian Gaussian beam method for solving the Schrödinger equation in the semi-classical regime. The idea of Eulerian Gaussian beams has been first proposed in [12]. In this paper we aim at two crucial computational issues of the Eulerian Gaussian beam method: how to carry out long-time beam propagation and how to compute beam ingredients rapidly in phase space. By virtue of the FBI transform, we address the first issue by introducing the reinitialization strategy into the Eulerian Gaussian beam framework. Essentially we reinitialize beam propagation by applying the FBI transform to wavefields at intermediate time steps when the beams become too wide. To address the second issue, inspired by the original phase flow method, we propose the backward phase flow method which allows us to compute beam ingredients rapidly. Numerical examples demonstrate the efficiency and accuracy of the proposed algorithms.     

大动态范围软X射线飞秒变像管

 为获得能够实际应用的飞秒时间分辨软X射线变像管,提出并完成了一种新的扫描变像管管型的理论设计。新管型采用五电极平面对称静电柱透镜,它易于对电子束进行强聚焦,且没有轴对称透镜的电子束聚焦交叉点,由此可以缩短变像管长度,减小渡越时间弥散和抑制空间电荷效应,从而提高动态范围和时间分辨率。通过模拟计算得到：在光电子初能量色散半高宽为1.6 eV、狭缝面积为10 mm×20 μm、时间分辨能力为500 fs时,软X射线变像管有用的动态范围约100倍。     

Two types of definitions for Rayleigh range

A comparison of the Rayleigh range between the two types of definitions (defined by the mean-squared beam width and the effective radius of curvature) is studied analytically and numerically, where the propagation of partially coherent beams both in free space and in atmospheric turbulence are considered. It is shown that the two types of the Rayleigh range definitions are consistent in free space. However, in turbulence the Rayleigh range defined by the mean-squared beam width is smaller than that defined by the effective radius of curvature. The main results obtained in this paper are illustrated by numerical calculation examples, where partially coherent Hermite–Gaussian (PCH–G) beams are considered.     

目标激光脉冲一维距离成像研究

根据激光雷达方程及粗糙面脉冲波束散射理论,提出了目标激光脉冲后向散射回波功率即激光一维距离像的计算表达式,并获得斜板、球和圆锥一维距离像的具体形式.数值计算结果与粗糙平板和圆锥激光脉冲回波强度实验数据比较,两者符合良好.数据分析表明,激光一维距离像曲线能够较好反映目标的纵向几何外形信息.我们着重讨论了入射激光脉冲宽度与目标径向尺寸对距离像的影响.上述研究可为激光波段的目标特征提取和识别提供理论依据.     

High dynamic range imaging method for interferometry

We demonstrate a method to easily and quickly extend the dynamic range imaging capabilities of the camera in a typical interferometric approach. The camera dynamic range is usually low and limited to 256 gray levels. Also, it is well known that one may have over or under-exposed regions in the interferogram (due to non-uniform illumination) which makes these image regions not reliable. In our proposed method it is not necessary to obtain or use the non-linear camera response curve in order to extend the camera dynamic range. We obtain a sequence of differently exposed interferograms, typically five or six; after that, we compute the corresponding normalized fringe patterns and modulation maps using a typical normalization method. These normalized patterns are combined through a temporal weighted average using as weights the corresponding modulation maps. We show a set of experimental results that prove the effectiveness of the proposed method.