核磁共振中的超辐射现象-辐射阻尼

在强磁场、高灵敏度和高浓度的条件下，质子自旋磁化强度在核磁共振检测线圈中产生的感应电流能将磁化强度本身驱回平衡态，该现象被称为辐射阻尼，其本质是无线电频段的超辐射。本文综述了近年来在核磁共振领域中得到充分研究的辐射阻尼效应，并用超辐射的观点进行了必要的讨论。     

核磁共振中的超辐射现象—辐射阻尼

在强磁场、高灵敏度和高浓度的条件下,质子自旋磁化强度在核磁共振检测线圈中产生的感应电流能将磁化强度本身驱回平衡态,该现象被称为辐射阻尼,其本质是无线电频段的超辐射。本文综述了近年来在核磁共振领域中得到充分研究的辐射阻尼效应,并用超辐射的观点进行了必要的讨论。     

辐射与发光 辐射测量与装置

O432．1 2005020877 辐射计校准技术的研究=Research of calibration of radi- ometers[刊,中]／王学新(西安应用光学所．陕西,西安 (710065)),杨照金…//应用光学.-2004,25(5)．-18-21 介绍了使用标准辐射计校准探测器的基本原理,对提 高光谱分辨率所用的标准选择问题作了讨论。通过讨论, 解决了如何选择探测器和辐射源的同题。通过探测器和     

辐射与发光 辐射测量与装置

O432．1 2005053222 绝对辐射计预测辐射电补偿的快速测量方法=Rapid measurement method of absolute radiometer by using fore- cast radiation in electrically heating compensationE刊,中]／ 禹秉熙(中科院长春光机所应用光学国家重点实验室．吉     

辐射与发光 辐射测量与装置

TH765.2 2006031857全天候气象专用B波段紫外辐照计的研制=Developmentof special meteorological UV-B radiometer for all-cli mate[刊,中]/张保洲(北京师范大学天文系,北京市重点应用光学实验室.北京(100875)) ,王术军…∥计量学报.—2006 ,27(1) .—25-27 ,38研制了一种可全天候应用的B波段紫外辐照度及紫外指数测试系统,着重介绍其主要技术环节及性能,与国内现用的同类仪器进行了性能比对,分析了仪器试观测的结果。证明该仪器在带外杂光、余弦响应、温度控制等方面具有优良的性能,软件功能齐全,操作方便。图3表1参6(杨妹清)辐射与…     

辐射与发光 辐射测量与装置

TH765．21 2005064029 国产紫外总日射表性能测试(Ⅱ):室外测试及国外同类产 品比较=Intercomparsion of China-made UV pyranometers (Ⅱ)——outdoor test and interecomparsion with foreign UV pyranometers[刊,中]/汤洁(中国气象科学研究院．北 京(100081)),王炳忠…∥太阳能学报．-2005,26(3)．- 313-320     

谈谈辐射

对辐射的认识是不断深化的。大家知道,处在不同温度和环境下的物体,都以电磁辐射形式发出能量,这被称为热辐射,能吸收全部外来辐射而毫无反射的理想热辐射体称为“黑体”。在黑体辐射中,存在各种波长     

沟道辐射

最近,人们发现,带电轻粒子在晶体沟道中运动发射与相干韧致辐射既有联系又有本质区别的新的辐射—沟道辐射。这种强度大、单色性好、高度定向且极化的辐射具有重要的理论和实验研究价值。本文讨论了沟道辐射的主要特征、实验进展状况、结果和装置及其可能的应用。并与其他有关辐射现象作了比较。     

辐射与发光 辐射测量与装置

O432．1 2005042456 利用Σ-△型模数转换器解决光辐射定标中弱信号测量的设计难题=Solution to the problem of weak signal meas- urement in radiometric calibration based on Σ-△ ADC[刊, 中]／李照洲(中科院安徽光机所遥感研究室．安徽,合肥 (230031)),郑小兵…／／光学技术．-2005,31(2)．-272- 275,278 采用一种低噪声高精度△-Σ型模数转换器(ADC),解决了多波段绝对辐亮度标准探测器中弱信号高精度测量     

沟道辐射

最近,人们发现,带电轻粒子在晶体沟道中运动发射与相干韧致辐射既有联系又有本质区别的新的辐射—沟道辐射。这种强度大、单色性好、高度定向且极化的辐射具有重要的理论和实验研究价值。本文讨论了沟道辐射的主要特征、实验进展状况、结果和装置及其可能的应用。并与其他有关辐射现象作了比较。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.