Wide-field prime focus corrector for the Anglo-Australian telescope

A wide-field (2°) prime focus corrector has been designed and built for the Anglo-Australian Telescope. The corrector incorporates an atmospheric dispersion compensator for the spectral range 365-1014 nm. A four-element lens system is the basis of the corrector, and it provides a satisfactory state of correction over a full field of 2°. The design of the lens system is described. The choice of layout is related directly to the intrinsic properties of each component.     

Vacuum-system design for the large-scale cryogenic gravitational wave telescope

The large-scale cryogenic gravitational wave telescope (LCGT) requires ultra-high vacuum tubes which the laser beams pass through. Two 3-km vacuum tubes are kept in ∼10⁻⁷ Pa of vacuum pressure so as to reduce scattering-effects due to residual gas molecules. The stainless-steel material with electro-chemical buffing is the most available for use as long tubes of 1 m in diameter. To reduce noises due to scattered light from the surface of tubes, a lot of baffles are inserted into the tubes.     

A synthetic aperture telescope based on a pair of gratings

A synthetic aperture is an effective approach to enhancement of the resolution of telescopes. In this paper, a new method to improve the resolution by using a pair of gratings is proposed. It allows collection of parts of the light diffracted from the object which could not previously reach the imaging device. This method improves the resolution and light energy utilization ratio of telescopes without introducing new chromatic aberration. An experiment for resolution testing was carried out and the feasibility and availability of the method were verified.     

A solid state microdosimeter based on a monolithic silicon telescope

A monolithic silicon telescope, consisting of a DeltaE and an E stage-detector ( approximately 1.9 microm and 500 microm thick, respectively), was coupled to a polyethylene converter in order to investigate the feasibility of a solid state microdosimeter with respect to the field-funnelling effect. This work discusses the preliminary results of an analytical approach for the correction of a spectrum measured with this silicon-based microdosimeter for tissue-equivalence and geometrical effects. The device was irradiated with 2.7 MeV monoenergetic neutrons at the INFN-Laboratori Nazionali di Legnaro (Legnaro, Italy). The non tissue-equivalence of silicon was corrected by exploiting the signals generated in the E-stage. The correction for the sensitive volume geometry was optimised by taking into account the track length distribution of the recoil-protons generated in the converter. The derived dose distribution of the energy imparted per event was compared to the one measured with a cylindrical tissue-equivalent proportional counter (TEPC). The agreement is satisfactory.     

Millimeter wave reimaging optics for the 100 m Green Bank telescope

Large bolometer arrays capable of operating at millimeter wavelengths are being built for astronomical use. For optimal sensitivity, high-quality optics with wide fields of view are needed. We report on the design of reimaging optics for use on the 100-m Green Bank telescope with a 64-element bolometer array.     

Wind profiling based on the optical beam intensity statistics in a turbulent atmosphere

Reconstruction of the wind profile from the statistics of intensity fluctuations of an optical beam propagating in a turbulent atmosphere is considered. The equations for the spatiotemporal correlation function and the spectrum of weak intensity fluctuations of a Gaussian beam are obtained. The algorithms of wind profile retrieval from the spatiotemporal intensity spectrum are described and the results of end-to-end computer experiments on wind profiling based on the developed algorithms are presented. It is shown that the developed algorithms allow retrieval of the wind profile from the turbulent optical beam intensity fluctuations with acceptable accuracy in many practically feasible laser measurements set up in the atmosphere.     

SENTIRAD—An innovative personal radiation detector based on a scintillation detector and a silicon photomultiplier

The alarming personal radiation detector (PRD) is a device intended for Homeland Security (HLS) applications. This portable device is designed to be worn or carried by security personnel to detect photon-emitting radioactive materials for the purpose of crime prevention. PRD is required to meet the scope of specifications defined by various HLS standards for radiation detection. It is mandatory that the device be sensitive and simultaneously small, pocket-sized, of robust mechanical design and carriable on the user's body. To serve these specialized purposes and requirements, we developed the SENTIRAD, a new radiation detector designed to meet the performance criteria established for counterterrorist applications. SENTIRAD is the first commercially available PRD based on a CsI(Tl) scintillation crystal that is optically coupled with a silicon photomultiplier (SiPM) serving as a light sensor. The rapidly developing technology of SiPM, a multipixel semiconductor photodiode that operates in Geiger mode, has been thoroughly investigated in previous studies. This paper presents the design considerations, constraints and radiological performance relating to the SENTIRAD radiation sensor.     

Increase in the modulation of an acoustic wave scattered from weakly stable vibrational states of bubbles

A theoretical analysis is made of the mechanism for nonlinear diagnostics of gas inclusions in a liquid. It is shown that the modulation of the scattered acoustic wave amplitude increases appreciably near critical values of the pump field corresponding to weakly stable bubble states. Pis’ma Zh. Tekh. Fiz. 24, 18–23 (August 26, 1998)     

Probing the wave fronts based on autocorrelation

We proposed an easy method for probing the wave fronts via a typical Fourier transform system. An amplitude only spatial light modulator (SLM) was set on the front focal plane of a Fourier lens to control the wave front transmittance. A CCD was set on the back focal plane of the Fourier lens to record the intensity patterns. The Fourier transform of the intensity pattern is the autocorrelation of the wave front passing through the SLM. When we choose suitable pixels of the SLM to permit the wave front passing through, the information from the wave front illuminating the pixels can be directly extracted from the Fourier transform of the diffraction intensity pattern without complicated calculations. The complex amplitude of the wave front illuminated on the SLM can be probed using the above-mentioned method. The simulation results certifying our theory were also given.     

Effect of telescope alignment on a stellar interferometer

For a ground-based stellar interferometer, we investigate the effect of wave-front distortions that are due to telescope alignment errors and other factors. We apply the results to the IR/Optical Telescope Array (IOTA) interferometer. We present the computational method used in our simulation program to calculate explicitly the wave-front shape from an arbitrarily misaligned telescope. We calculate the wave-front shape and variance for a suite of misalignment conditions and interpret these results to find allowable tolerances on the positions and tilts of the telescope mirrors. We calculate the expected Strehl ratios from a total of ten types of factor, including telescope alignment, that are expected to be important in a real interferometer. Ranking the expected wave-front perturbations, we find that three of them, the wave-front curvature from atmospheric turbulence, the servo system time constant, and the flatness of the relay optics surfaces, are more significant than the telescope alignment factor. We compare observational experience at IOTA with our model estimate of the overall Strehl ratio in the visual and the infrared, finding moderately good agreement and, more important, a guide for future instrumental improvements.     

"猫眼"系统中离焦量的变化对回波功率的影响

阐述了“猫眼效应”的基本原理，给出了离焦时的“猫眼”模型，采用光线追迹的方法着重分析了离焦时“猫眼”系统的回波功率的变化情况。通过分析可看出，后向移动光敏面的可调制范围远远大于前向移动光敏面的可调制范围，这使得应用“猫眼”系统后向离焦量的改变，来改变回波功率的大小，使其能传递信息成为可能。     

Surface-roughness measurement based on the intensity correlation function of scattered light under speckle-pattern illumination

The statistical properties of speckle patterns generated from a rough surface under a fully developed static speckle-pattern illumination are examined. The roughness dependence of the intensity autocorrelation function is studied and utilized to characterize typical engineering surfaces with anisotropic roughness. The speckle patterns under investigation are recorded by use of a CCD technique and are then analyzed by digital image processing algorithms to obtain a parameter that describes the surface roughness. It is shown that an in-process surface inspection can be achieved by this method.     

Location of the elevation axis in a large optical telescope

Proposed designs for the next generation of large optical telescopes favor a tripod or quadrupod secondary support, and a primary supported from the back, but it is not yet clear whether the elevation axis should be in front of the primary or behind it. A study is described of the effect of elevation-axis location on key performance parameters (fundamental frequency, blockage, and wind-induced secondary decenter) for a 30-m Cassegrain telescope with amount configuration that is typical of the new designs. For a fast (e.g., f/1) primary, the best location for the elevation axis is behind the primary. The penalty for moving the elevation axis in front of the primary is roughly a 40% decrease in fundamental frequency and a corresponding reduction in the control bandwidth for pointing and optical alignment.     

Simulation of bubble motion in a compressible liquid based on the three dimensional wave equation

A simulation model for bubble motion in a compressible liquid is developed based on the linear wave equation. At the initial stage, the bubble is assumed to be spherical and the wave equation is simplified as a one dimensional ordinary equation in the radial direction through the prophase approximation. When time becomes much larger than that required for a disturbance to travel across the bubble at the speed of the sound, the obtained integral equation is approximated by keeping the term of the first order in terms of the characteristic Mach number, through the anaphase approximation. An equation is introduced to unify the approximations in these two phases, which is then used over the entire simulation period. The problem at each time step is solved by a three dimensional boundary element method. The convergence study has been first taken with meshes and time steps. Comparison is made with the analytical solution for spherical bubble in compressible liquid and good agreement is found. Further comparison is made for a bubble in an incoming acoustic wave. Extensive simulations are then made for a bubble in various conditions, including the cases with solid boundary effect, free surface effect, buoyancy effect, as well as for interactions between bubbles.     

Engineering calculation of the characteristics of a filtration-combustion wave based on a one-dimensional two-temperature model

The authors present a method for determining the characteristics of a filtration-combustion wave that uses physically substantiated simplifications of a one-dimensional two-temperature model of filtration flow with Arrhenius kinetics. Explicit, physically transparent dependences for the ignition temperature, wave velocity, and maximum skeleton temperature are obtained. A brief review of and a comparison with other one-dimensional methods and with a numerical calculation are given. This method is shown to be superior to more cumbersome analytical two-temperature methods in accuracy. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 3, pp. 424–432, May–June, 1998.     

Kalman filter tracking in a Cherenkov neutrino telescope

The reconstruction of tracks in underwater Cherenkov neutrino telescopes is strongly complicated due to large background counting rate originates from ⁴⁰K beta decay and to the electromagnetic showers accompanying high energy muons together with the effects of light propagation in the water, in particular the photon scattering. These two effects lead to a non-linear problem with a non-Gaussian measurement noise. A method for track reconstruction based on Kalman filter approach in this situation is presented. We use Gaussian Sum Filter algorithm to take into account non-Gaussian process noise. While usual Kalman filter estimators based on linear least-square method are optimal in case all observations are Gaussian distributed, the Gaussian Sum Filter offers a better treatment of non-Gaussian process noise and/or measurement errors when these are modeled by Gaussian mixtures. As an example of the application, the results of muon track reconstruction in NEMO underwater neutrino telescope are presented as well as the comparison of its capability with other standard track reconstruction methods.     

A combined neutron and gamma-ray multiplicity counter based on liquid scintillation detectors

Multiplicity counters for neutron assay have been extensively used in materials control and accountability for nonproliferation and nuclear safeguards. Typically, neutron coincidence counters are utilized in these fields. In this work, we present a measurement system that makes use not only of neutron (n) multiplicity counting but also of gamma-ray (γ) multiplicity counting and the combined higher-order multiples containing both neutrons and gamma rays. The benefit of this approach is in using both particle types available from the sample, leading to a reduction in measurement times compared with single-particle measurements. We present measurement results of n, γ, nn, nγ, γγ, nnn, nnγ, nγγ and γγγ multiples emitted by Mixed-Oxide (MOX) samples measured at Idaho National Laboratory (INL). The MOX measurement is compared to initial validation of the detection system done using a ²⁵²Cf source. The dual radiation measuring system proposed here uses extra measurables to improve the statistics when compared to a neutron-only system and allows for extended analysis and interpretation of sample parameters. New challenges such as the effect of very high intrinsic gamma-ray sources in the case of MOX samples are discussed. Successful measurements of multiple rates can be performed also when using high-Z shielding.     

3D散乱数据点分段二次逼近的曲面拟合

为进一步提高曲面重构的保形性及高效性,提出了一种自动构建光顺三角曲面的方法．该法首先通过构建三角形元覆盖边界域来构建一张曲面近似粗网,然后从点集中不断添加新点直至达到指定的容差,在每个插入数据点处构造C1连续的分片二次逼近面片,最终整体的C¹曲面由各三角形上的曲面片拼合而成．最后给出了该方法在真实点集上的运用结果并与其他方法所构造的逼近曲面形状进行了比较,结果表明,该方法对密集3D散乱数据点建模有效,生成的曲面质量高,误差小．该方法也适用于数据精简．     

High-frequency surface wave radar based on a sea floating antenna concept

The concept of sea floating antenna array is to replace a conventional coastal receive unit by a sea floating array, constituted of a set of receive buoys. Waves and wind introduce movements of buoys in the array which generate disturbances in the array radiation pattern. In this paper, compensation methods for vertical and horizontal displacements are presented. This paper introduces algorithms for both displacements which are tested following different sea states. Then, these algorithms can be combined in series, providing a simple method to optimise the radiation pattern of the deformed array.