A high-performance polarimeter for medium-energy neutrons

A polarimeter for medium-energy neutrons is described. This polarimeter uses the analyzing power of n–p scattering which is typically +0.50 for laboratory neutron scattering angles near 20° in the energy range from 50 MeV to 1 GeV. Hydrocarbon organic scintillators are employed as “active” scatterers. Calibration data for the analyzing power and the efficiency of the polarimeter are presented.     

Polarized radiance distribution measurement of skylight. II. Experiment and data

Measurements of the skylight polarized radiance distribution were performed at different measurement sites, atmospheric conditions, and three wavelengths with our newly developed Polarization Radiance Distribution Camera System (RADS-IIP), an analyzer-type Stokes polarimeter. Three Stokes parameters of skylight (I, Q, U), the degree of polarization, and the plane of polarization are presented in image format. The Arago point and neutral lines have been observed with RADS-IIP. Qualitatively, the dependence of the intensity and polarization data on wavelength, solar zenith angle, and surface albedo is in agreement with the results from computations based on a plane-parallel Rayleigh atmospheric model.     

Rotating-polarizer polarimeter for accurate retardance measurement

We demonstrate an automated polarimeter based on a rotating polarizer for the measurement of linear retardance independent of laser power and detector gain. The retardance is found when a curve is fitted to a unique normalization of the intensity response of the polarimeter over a range of input polarizer orientations. The performance of this polarimeter is optimal for measurements of quarter-wave retardance and minimal for half-wave retardance. Uncertainties are demonstrated by measurements on six stable double Fresnel rhombs of nominal quarter-wave retardance, yielding expanded uncertainties between 0.031 degrees and 0.067 degrees . The accuracy has also been verified by blind comparisons with interferometric and modified null retardance measurement techniques.     

Inline fiber-optic polarization analyzers for sensor application

Theoretical and experimental investigations of a new type of inline fiber-optic polarization analyzer are described in this paper. The discussed devices are based on a polarimeter, as well as a Sagnac interferometer configuration, and give the possibility to detect the full polarization changes. Detection of the polarization state as well as its degree in real time by the systems containing a standard single-mode fiber and application of appropriate modulation technique is a new property of the arrangement. The comparison of the described systems based on experimental device investigation is also presented in this paper.     

Multiphase microwave dielectrics

Several types of multiphase ceramic materials with excellent microwave (MW) dielectric properties have been considered. Studied materials were based on complex niobates and titanates with various crystal structures in which very high values of the MW quality factors (Q) can be attained. Slight compositional changes in the complex oxide systems have been shown to induce rather combined effect on the cation arrangement of separate crystal phases as well as on the microstructure and phase composition of multiphase ceramic materials. As a consequence, the ways to tailor MW dielectric parameters of the ceramics through a proper adjustment of both structure and distribution of enclosed phases have been presented and discussed. The examples of the multiphase MW dielectrics with enhanced properties have also been presented.     

Ground-based full-sky imaging polarimetry of rapidly changing skies and its use for polarimetric cloud detection

For elimination of the shortcomings of imaging polarimeters that take the necessary three pictures sequentially through linear-polarization filters, a three-lens, three-camera, full-sky imaging polarimeter was designed that takes the required pictures simultaneously. With this polarimeter, celestial polarization patterns can be measured even if rapid temporal changes occur in the sky: under cloudy sky conditions, or immediately after sunrise or prior to sunset. One of the possible applications of our polarimeter is the ground-based detection of clouds. With use of the additional information of the degree and the angle of polarization patterns of cloudy skies measured in the red (650 nm), green (550 nm), and blue (450 nm) spectral ranges, improved algorithms of radiometric cloud detection can be offered. We present a combined radiometric and polarimetric algorithm that performs the detection of clouds more efficiently and reliably as compared with an exclusively radiometric cloud-detection algorithm. The advantages and the limits of three-lens, three-camera, full-sky imaging polarimeters as well as the possibilities of improving our polarimetric cloud detection method are discussed briefly.     

Nanosphere monolayer-templated, ion-assisted nanofeature etching in dielectric materials: a numerical simulation of nanoscale ion flux topography

The results of numerical simulations of nanometer precision distributions of microscopic ion fluxes in ion-assisted etching of nanoscale features on the surfaces of dielectric materials using a self-assembled monolayer of spherical nanoparticles as a mask are presented. It is shown that the ion fluxes to the substrate and nanosphere surfaces can be effectively controlled by the plasma parameters and the external bias applied to the substrate. By proper adjustment of these parameters, the ion flux can be focused onto the areas uncovered by the nanospheres. Under certain conditions, the ion flux distributions feature sophisticated hexagonal patterns, which may lead to very different nanofeature etching profiles. The results presented are generic and suggest viable ways to overcome some of the limitations of the existing plasma-assisted nanolithography.     

Design and initial performance of SHARP, a polarimeter for the SHARC-II camera at the Caltech Submillimeter Observatory

We have developed a foreoptics module that converts the Submillimeter High Angular Resolution Camera generation II (SHARC-II) camera at the Caltech Submillimeter Observatory into a sensitive imaging polarimeter at wavelengths of 350 and 450 microm. We refer to this module as "SHARP." SHARP splits the incident radiation into two orthogonally polarized beams that are then reimaged onto opposite ends of the 32 x 12 pixel detector array in SHARC-II. A rotating half-wave plate is used just upstream from the polarization-splitting optics. The effect of SHARP is to convert SHARC-II into a dual-beam 12 x 12 pixel polarimeter. A novel feature of SHARP's design is the use of a crossed grid in a submillimeter polarimeter. Here we describe the detailed optical design of SHARP and present results of tests carried out during our first few observing runs. At 350 microm, the beam size (9 arc sec), throughput (75%), and instrumental polarization (<1%) are all very close to our design goals.     

Snapshot imaging polarimeter using modified Savart polariscopes

In this paper, based on the combination of two modified Savart polariscopes, we present a snapshot imaging polarimeter and show that the carrier frequency is two times higher than that of the snapshot imaging polarimeter using two conventional Savart polariscopes. The signal-to-noise ratio and the spatial resolution of imagery in each channel are improved due to the increase of the carrier frequency when we filter the channels to recover the Stokes vector images. Moreover, compared with conventional imaging polarimetry, the remarkable advantage of the proposed instrument is that it is also simple, compact, miniature, snapshotted, and static (no moving parts). To demonstrate the feasibility of the proposed snapshot imaging polarimeter, the numerical simulation of a design example is presented in detail.     

Optical Heterodyne Polarimeter for Studying Space-and Time-dependent State of Polarization of Light

Abstract

This paper describes an optical heterodyne polarimeter with a photodetector array by which the space- and time-dependent state of polarization (SOP) of light can be determined. Since no optical components for polarization control are used, the time response of the polarimeter is free from such components, but is basically limited to the frequency bandwidth of the photodetector array used. The signal and local oscillator beams are coherently photomixed to generate a beat photocurrent at every pixel of the photodetector array. The orthogonal linearly polarized two-frequency components of the local oscillator beam are superimposed with their respective counterpart orthogonally decomposed components of the elliptically polarized signal beam. The generated beat-photocurrent offers the significant physical parameters required for the determination of the space- and time-dependent SOP. The performance principle of the polarimeter is explained and confirmed experimentally.     

高碾压混凝土坝智能碾压理论研究

给出了高碾压混凝土坝智能碾压的概念及实现过程,提出了大坝实时监控和智能反馈控制的原理;在实时分析压实指标的基础上,建立了大坝压实质量多元回归模型,进而提出了碾压混凝土坝压实度全仓面实时评价方法;实现了施工过程中碾压机工作性态的自适应调整,确保碾压机速度、激振力、碾压遍数和压实厚度等全过程达标,可有效保证碾压质量,提高施工效率,为碾压混凝土坝建设质量控制提供了一条新的途径。     

Two-dimensional polarimeter with a charge-coupled-device image sensor and a piezoelastic modulator

We present the first measurements and scientific observations of the solar photosphere obtained with a new two-dimensional polarimeter based on piezoelastic modulators and synchronous demodulation in a CCD imager. This instrument, which is developed for precision solar-vector polarimetry, contains a specially masked CCD that has every second row covered with an opaque mask. During exposure the charges are shifted back and forth between covered and light-sensitive rows synchronized with the modulation. In this way Stokes I and one of the other Stokes parameters can be recorded. Since the charge shifting is performed at frequencies well above the seeing frequencies and both polarization states are measured with the same pixel, highly sensitive and accurate polarimetry is achieved. We have tested the instrument in laboratory conditions as well as at three solar telescopes.     

对两面临空矿段的控制爆破

对于某露天矿开采两面临空矿段的控制爆破,采取了以下措施:①利用地形、地物的优势合理地选取爆破参数和布孔;②精确计算每孔装药量,并进行适当调整;③利用两面临空条件,设计起爆网路及延时间隔时间,巧妙地利用起爆时差使爆破产生的反作用力互相抵消。这些措施确保了施工安全及爆破质量,获得了满意的效果。     

High-resolution birefringence imaging in three-dimensional stressed models by fourier polarimetry

Recently several polarimetric techniques have been suggested, designed deliberately for automatic whole-field birefringence imaging in photoelastic models with essentially three-dimensional stresses. In general, these techniques are feasible for mapping three optical parameters that determine birefringence in a given case. However, the difficulty in attaining a high level of data accuracy over the whole image persists. There remains a problem of precise imaging in regions where the mutual interference of three given parameters inevitably causes accuracy deterioration. We show how to correct such imperfections in an imaging polarizer-sample-analyzer (PSA) Fourier polarimetry technique, as suggested earlier [Appl. Opt. 41, 644 (2001)]. The given technique (a method developed so that it maps the phase, the azimuth, and the ellipticity angles of an elliptic retarder) particularly fails to provide precise imaging in regions where the phase is either close to null or approaches pi-multiple values and in intervals where the ellipticity angle falls into the proximity of ?pi/4 values. These drawbacks can be successfully overcome by incorporation of a compensator into a PSA polarimeter arrangement. Although use of a compensator in the polarimeter makes the original technique more complicated, we demonstrate that the compensator allows two important issues to be resolved. First, it provides precise imaging for each of three optical parameters through the whole accessible intervals of the parameters regardless of the absolute value of the parameter. In addition, it gives a sign of phase that remains undefined in the PSA techniques. Theoretical considerations are presented and are followed by experimental data that illustrate the improved accuracy capabilities of the compensator-enhanced technique.     

Optical activity measurement by use of a balanced detector optical heterodyne interferometer

What we believe to be a novel amplitude sensitive optical heterodyne polarimeter in which a Zeeman laser is associated with balanced detector detection was set up. The aim was to measure the optical activity of a quartz crystal with a Cornu depolarizer at high accuracy. The features of this novel polarimeter, which include the use of a two-frequency laser that ensures the accuracy of the measurement, are discussed. Furthermore, the detection sensitivity of the optical activity of a quartz crystal was measured as 8.5x10(-10). To our knowledge, this is the highest sensitivity obtained for optical activity measurement of a quartz crystal when the error of the measurement is also analyzed.     

Measurements and simulations of polarization states of underwater light in clear oceanic waters

Polarization states of the underwater light field were measured by a hyperspectral and multiangular polarimeter and a video polarimeter under various atmospheric, surface, and water conditions, as well as solar and viewing geometries, in clear oceanic waters near Port Aransas, Texas. Some of the first comprehensive comparisons were made between the measured polarized light, including the degree and angle of linear polarization and linear Stokes parameters (Q and U), and those from Monte Carlo simulations that used concurrently measured water inherent optical properties and particle volume scattering functions as input. For selected wavelengths in the visible spectrum, measured and model-simulated polarization characteristics were found to be consistent in most cases. Measured degree and angle of linear polarization are found to be largely determined by an in-water single-scattering model. Model simulations suggest that the degree of linear polarization (DoLP) at horizontal viewing directions is highly dependent on the viewing azimuth angle for a low solar elevation. This implies that animals can use the DoLP signal for orientation.     

Full-field characterization of a twisted nematic liquid-crystal device using equivalence theorem of a unitary optical system

Based on the equivalence theorem of a unitary optical system, we proposed an analytical approach to characterize the cell parameters of a twisted nematic liquid-crystal device (TNLCD) with full-field resolution. The spatial distribution of three characteristic parameters of a TNLCD was measured by using a polarizer-sample-analyzer imaging polarimeter so that the untwisted phase retardation, cell thickness, and twisted angle of a TNLCD can be directly calculated through the explicit expressions as a function of the characteristic parameters. The measured results agree well with the given values. This method can be implemented for characterization of a TNLCD in the manufacturing process.     

全极化微波辐射计遥感海面风场的 关键技术和科学问题

全极化微波辐射计是一种新型的微波遥感器,它不但测量目标微波辐射信号的两个正交极化分量,并且测量两个正交极化分量的复相关量。这些相关信息对于表面微波辐射的各向异性更加敏感,这样就提供了测量海面风场的一种手段。 文章在介绍国内外全极化微波辐射计现状和特点的基础上,首先对于全极化微波辐射计遥感海面风场的原理及其影响因素进行分析;然后,从全极化微波辐射计的硬件设计和定标两个方面论述了硬件实现的关键技术问题;最后,对于风场反演的有关科学问题进行分析,重点论述了风场反演算法建立的关键,主要技术指标对于风场反演误差的影     

High-sensitivity two-dimensional thermal- and mechanical-stress-induced birefringence measurements in a Nd:YAG rod

A novel polarimeter for measuring the two-dimensional (2D) thermal- and mechanical-stress-induced birefringence in solid-state laser materials such as Nd:YAG is proposed. Using this device, we could sensitively measure the direction of the principal birefringence axis as well as the phase shift δ with sign when δ < π/4. The 2D thermal- and mechanical-stress-induced birefringence in a laser-diode-pumped Nd:YAG rod was successfully measured with the proposed polarimeter. We also found an active quarter-wave Nd:YAG phase retarder.