瑞利散射多普勒测风激光雷达的校准

 在进行实际风速测量之前,对于新研制的测风激光雷达系统进行校准,可以验证并提高风速测量的准确性。根据瑞利散射多普勒激光雷达的测量原理,提出了利用瑞利散射谱和米散射谱之间的关系,采用运动硬目标实现对瑞利散射多普勒测风激光雷达进行校准的方法。设计了对瑞利散射多普勒测风激光雷达进行校准的实验系统,并给出了详细的校准步骤。     

相干瑞利散射海水水下温度测量技术的理论研究

海水水下温度的快速大范围测量是海洋监测的重要内容,在民用和军事领域都有着至关重要的意义,本文提出了采用相干瑞利散射方法测量海水水下温度的新方法:用宽带高速光电探测器接收本振激光和海水后向瑞利散射光相干产生的差频信号,进行傅里叶变换分析获取海水瑞利散射展宽谱,从而反演海水温度,首先从海水的热力学特性出发,对利用瑞利散射谱测量海水水下温度的基本原理进行了理论研究和软件模拟;然后对采用相干探测测量海水瑞利散射谱的测量方法进行了理论分析和软件模拟;在此基础上对瑞利散射海水水下温度测量精度进行了分析,得出当水体瑞利散射频谱半宽度测量精度为1 MHz时,测温精度约为0.35 K。     

Experimental study on the surface stress measurement with Rayleigh wave detection technique

In this paper, experimental study on the surface stress measurement of a metallic material based on the Rayleigh wave acoustoelastic theory is introduced. A Rayleigh wave acoustoelastic formula deduced by Husson is optimized to estimate the surface stress of the material. Two micro Rayleigh wave transducers with 5 MHz frequency one of which is used for acoustic pulse emitter and another for receiver are used to determine the time of flight of Rayleigh wave propagating in a certain distance along the surface of the material. The difference in time of flight between two ultrasonic signals obtained in stressed and unstressed object surface is identified by the digital correlation method. A specimen made of Q235 steel and applied with tensile load is used for calibration to obtain the acoustoelastic coefficients of Q235 steel. Furthermore, some principal factors which may result in errors in the experiment are discussed and some measurements are proposed to prevent these errors. Finally the surface stress of a cantilever beam is detected by the Rayleigh wave acoustoelastic technique and the experimental result is well compared with the theoretical value.     

Evaluation of a liquid ionization chamber for relative dosimetry in small and large fields of radiotherapy photon beams

Commissioning and quality assurance of radiotherapy linear accelerators require measurement of the absorbed dose to water, and a wide range of detectors are available for absolute and relative dosimetry in megavoltage beams.In this paper, the PTW microLion isooctane-filled ionization chamber has been tested to perform relative measurements in a 6 MV photon beam from a linear accelerator. Output factors, percent depth dose and dose profiles have been obtained for small and large fields. These quantities have been compared with those from usual detectors in the routine practice. In order to carry out a more realistic comparison, an uncertainty analysis has been developed, taking type A and B uncertainties into account.The results present microLion as a good option when high spatial resolution is needed, thanks to its reduced sensitive volume. The liquid filling also provides a high signal compared to other detectors, like that based on air filling. Furthermore, the relative response of microLion when field size is varied suggests that this detector has energy dependence, since it is appreciated an over-response for small fields and an under-response for the large ones. This effect is more obvious for field sizes wider than 20 × 20 cm², where the differences in percent depth dose at great depths exceed the uncertainties estimated in this study.     

Ultraviolet filtered Rayleigh scattering temperature measurements with a mercury filter

We report the development of ultraviolet filtered Rayleigh scattering as a diagnostic tool for measurements of gas properties. A frequency-tripled narrow-linewidth Ti:sapphire laser illuminates a sample, and Rayleigh scattered light is imaged through a mercury-vapor absorption filter. Working in the ultraviolet improves the signal-to-noise ratio compared with that previously obtained in the visible as the result of an enhanced scattering cross section as well as the nearly ideal properties of the mercury filter. Tuning the laser through the absorption notch of the filter is a means of probing the scattering line shape, which contains temperature information. Temperature measurements of air are shown to have uncertainties of less than 3%.     

Research in absolute calibration of single photon detectors by means of correlated photons

There are two general methods in radiometric calibration of detectors, one is based on radiation sources and the other based on detectors. Because the two methods need to establish a primary standard of high precision and a transfer chain, precision of the standard will be reduced by extension of the chain. A new calibration method of detectors can be realized by using correlated photons generated in spontaneous parametric down-conversion (SPDC) effect of nonlinear crystal, without needing transfer chain. Using 351.1-nm output of a tunable laser to pump β-barium borate (BBO) crystal, an absolute calibration experimental system of single photon detectors based on correlated photons is performed. The quantum efficiency of photomultiplier (PMT) at 702.2 nm is measured by the setup. Advantages of this method over traditional methods are also pointed out by comparison.     

Quantum efficiency calibration of opto-electronic detector by means of correlated photons method

A new calibration method of detectors can be realized by using correlated photons generated in spontaneous parametric down-conversion (SPDC) effect of nonlinear crystal.An absolute calibration system of detector quantum efficiency is performed.And its principle and experimental setup are introduced.A continuouswave (CW) ultraviolet (351 nm),diode-pumped,frequency-doubled,and solid-state laser is used to pump BBO crystal.The quantum efficiencies of the photomultiplier at 633,702,and 789 nm are measured respectively.The coincidence peaks are observed using coincidence circuit.Some measurement factors including the filter bandwidth of trigger channel,the detector position alignment and polarization of the pump light are analyzed.The uncertainties of this calibration method are also analyzed,and the relative uncertainties of total calibration are less than 5.8%.The accuracy of this method could be improved in the future.     

Optical measurement of acoustic pressure amplitudes-at the sensitivity limits of Rayleigh scattering

Rayleigh scattering is a measurement technique applicable for the determination of density distributions in various technical or natural flows. The current sensitivity limits of the Rayleigh scattering technique were investigated experimentally. It is shown that it is possible to measure density oscillations caused by acoustic pressure oscillations noninvasively and directly. Acoustical standing waves in a rectangular duct were investigated using Rayleigh scattering and compared to microphone measurements. The comparison showed a sensitivity of the Rayleigh scattering technique of 75 Pa (7·10(-4) kg/m(3)) and a precision of 14 Pa (1·10(-4) kg/m(3)). Therefore, it was also shown that Rayleigh scattering is applicable for acoustic measurements.     

Soot sublimation studies in a premixed flat flame using laser-induced incandescence (LII) and elastic light scattering (ELS)

Laser-induced incandescence (LII) as a diagnostic technique is based on rapid heating of soot particles to temperatures of several thousand Kelvin and subsequent detection of the thermal radiation from the laser-heated particles. At such high temperatures, soot sublimation effects must be considered when estimating uncertainties in LII measurements. In this work we have investigated the use of various laser fluences in LII using a Nd:YAG laser at 1,064 nm. Using another Nd:YAG laser at 532 nm, the elastic light scattering (ELS) signal from soot particles heated by the 1,064-nm laser was monitored. This approach makes it possible to determine at which fluence of the LII laser soot sublimation starts to become visible as a decrease in the ELS signal. By performing the measurements at various heights in a premixed sooting flat ethylene/air flame, the fluence threshold above which the ELS signal decreased was found to be higher at the lower flame heights corresponding to younger, smaller and less aggregated particles. The results from this work indicate that the different fluence thresholds for sublimation may be explained by a lower absorption function E(m) for the younger soot particles.     

Application of 30-MHz acoustic scattering to the study of human red blood cells

A technique for simultaneously measuring the scattering amplitude of individual particles at two angles is applied to human red blood cells. Using a Rayleigh scattering model, the density and compressibility of the cells may be determined given a priori knowledge of their volume. A calibration method relying on measurements of the bulk properties of particle suspensions is described. Red cell properties in hypotonic and hypertonic hosts are compared with a homogeneous mixture model, and a linear relation between hemoglobin content and scattering amplitude at a 90 deg scattering angle is established.     

三维漫射光谱法检测猪肉嫩度的初步研究

猪肉是光的强散射物质,嫩度是评价猪肉品质优劣的重要标准之一,提出一种基于三维漫射光谱法的猪肉嫩度检测方式。将猪肉样本更多的散射信息引入光谱分析中。利用实验室搭建的数据采集系统,通过采集距光源入射点不同距离处的样本漫反射光信号构建了64个猪肉样本的三维漫射光谱。经过小波消噪处理后,利用多维偏最小二乘法(NPLS)建立了三维漫射光谱与猪肉嫩度之间的分析模型,模型的校正决定系数R2_Cal是0.883 1,校正标准差RMSEC是3.685 0N,预测决定系数R2_Pred是0.874 7,预测标准差RMSEP是3.9756N。实验结果表明, 与常规的漫反射光谱法相比,三维漫射光谱法所建立的猪肉嫩度NPLS模型具有更高的校正精度和预测稳健性,有望为猪肉嫩度及其他品质的快速检测提供一种新的途径。     

基于虚拟刻度原理对放射性体源效率刻度方法的发展

采用蒙特卡罗模拟计算的方法,标定能够适用于不同HPGe探测器上的体源虚拟点源位置,需要对点源、体源的探测效率进行模拟计算。通过²⁴¹Am、¹³⁷Cs、⁶⁰Co点源和体源研究了HPGe晶体尺寸、类型对它们的虚拟点源位置的影响,模拟结果表明²⁴¹Am虚拟点源位置随着探测器尺寸、类型的不同呈现明显的差异性,说明虚拟刻度原理对于探测器表面的小体积样品测量在低能区间是不可取的,最后采用¹³⁷Cs、⁶⁰Co源得出体源高度与虚拟点源位置的半经验公式。通过实验室两台HPGe探测系统对尺寸Φ70 mm×65 mm标准土壤体源的探测效率进行计算,与模拟探测效率值、虚拟点源效率表征结果对比分析,验证了拟合一组表征虚拟点源位置的半经验公式是可行的。实验结果表明,对γ能量区间在300～2 000 keV进行体源的虚拟刻度时,选择可靠的定标源即可建立体源和虚拟点源位置的关系。这为解决监测工作中样品与探测器之间重复进行探测效率校准的问题提供了新的途径。     

FNTD radiation dosimetry system enhanced with dual-color wide-field imaging

At high neutron and photon doses Fluorescent Nuclear Track Detectors (FNTDs) require operation in analog mode and the measurement results depend on individual crystal color center concentration (coloration). We describe a new method for radiation dosimetry using FNTDs, which includes non-destructive, automatic sensitivity calibration for each individual FNTD. In the method presented, confocal laser scanning fluorescent imaging of FNTDs is combined with dual-color wide field imaging of the FNTD. The calibration is achieved by measuring the color center concentration in the detector through fluorescence imaging and reducing the effect of diffuse reflection on the lapped surface of the FNTD by imaging with infra-red (IR) light. The dual-color imaging of FNTDs is shown to provide a good estimation of the detector sensitivity at high doses of photons and neutrons, where conventional track counting is impeded by track overlap.     

A new technique for measuring radon exposure at working places

A new technique has been developed based on passive diffusion sampling and alpha track detection for monitoring radon exposure at working places. It is based on a device to be turned on and off at monitoring sites to permit accurate measurements of timed exposures. This technique is useful for radioprotection applications on personal and area monitoring of radon volume activity: timed measurement intervals and addition of sequential exposures. Additionally, the device allows accurate calibration with the application of radon reference atmospheres. Calibration facilities have been realized which allow starting detector exposure only at stationary conditions to avoid effects of varying radon concentration during exposure of passive integrating detectors. The contribution of the initial transient to the overall exposure ranged from about 3% to 10% according to calibration protocol. Experimental data evidence better performances of this new technique with respect to other measuring devices for integrating measurements based on radon diffusion samplers and polymeric nuclear track detectors (CR-39, LR-115 and polycarbonate). A better accuracy of calibration factor is obtained. The technical apparatus is presented and preliminary results described.     

Suitability of laser Doppler velocimetry for the calibration of pressure microphones

The details of a new approach for absolute calibration of microphones, based on the direct measurement of acoustic particle velocity using laser Doppler velocimetry (LDV), are presented and discussed. The calibration technique is carried out inside a tube in which plane waves propagate and closed by a rigid termination. The method developed proposes to estimate the acoustic pressure with two velocity measurements and a physical model. Minimum theoretical uncertainties on the estimated pressure and minimum measurable pressure are calculated from the Cramer Rao bounds on the estimated acoustic velocity amplitude and phase. These uncertainties and the minimum measurable pressure help to optimize the experimental set up. Acoustic pressure estimations performed with LDV are compared with acoustic pressures obtained with a reference microphone. Measurements lead to a minimum bias of 0.006 dB and a minimum uncertainty of 0.013 dB on the acoustic pressure estimation for frequencies 1360 Hz and 680 Hz.     

Search for particles of cold nonbarion dark matter in the EDELWEISS-II experiment

The EDELWEISS-II experiment is aimed at direct detection of weakly interacting massive particles (WIMP) considered as main candidates for the role of nonbarion dark matter. In the experiment, a search for rare WIMP-Ge scattering events is performed using HPGe-detectors-bolometers at a temperature of 20 mK. Because of different ionization losses of recoil nuclei and electrons, the use of detectors allowing simultaneous measurement of phonon and ionization signals enables background events to be suppressed very efficiently. To suppress actively the remained source of events simulating the WIMP signature, namely, the surface events with incomplete charge collection, detectors with coplanar ring electrodes have been developed for the EDELWEISS-II facility. The experimental coefficient of suppression of all EDELWEISS-II background components with the help of calibration measurements allows 3500 kg⋅day statistics to be accumulated with the expected zero level of the background events in the region of search for the WIMP. This enables the spinindependent WIMP-nucleon scattering events to be registered given that their cross section is greater than 10^-45 cm² (10^-9 pb) predicted by a wide class of the SUSY models.     

Quantum information and microscopic measuring instruments

The consideration of measuring instruments as macroscopic bodies leads to neglect of the microscopic processes that occur during measurements. This disregard is not justified in general cases. As an example of measurements using microscopic instruments, the scattering of a photon by an electron with electron interference at two slits(Compton effect) was used. The amount of information that can be obtained in such a process is inversely proportional to the wavelength of the incident photon. At large photon wavelengths(soft measurements), the pure state of the electron can be disrupted by an arbitrarily small extent; accordingly, the amount of information extracted in such an experiment is also arbitrarily small. It is shown that the energy price for a bit obtained in such a measurement tends toward a constant value for increasing the photon wavelength. Microscopic instruments can be used in situations where energy costs for measurements are important.     

Electron loss spectra from a W(001)surface

A high resolution energy dispersion analysis of the electron loss spectra (ELS) from a W(001) surface has been done with a specular reflexion geometry. The non-dispersive ELS correlates well with a combination of the bulk and surface loss functions determined from recent optical data whereas the dispersive ELS showed significant differences. Multiple plasmon losses were demonstrated while for the interband losses a momentum selection method has been demonstrated to separate scattering in the surface region from that in the bulk.     

近红外漫反射光谱无损检测乳粉蛋白质的研究

利用近红外漫反射光谱技术对奶粉蛋白质含量的快速无损检测进行了研究。挑选来自国内不同地区的29种奶粉,以化学分析值作参比,采用偏最小二乘回归算法建立奶粉光谱信息和蛋白质含量的定量模型,预测均方根差(RMSEP)为0.687%。采用波长选择对模型进行优化后,波长点从1 558个减为11个,大大加快了运算速度,同时还在一定程度上提高了模型的精度。为了减小颗粒大小不均匀和粒子表面非特异性散射的影响,对光谱数据进行了标准正态变量(SNV)变换和多元散射校正(MSC),结果表明这两种方法是有效的,得到RMSEP减小了约37%。研究结果表明,近红外漫反射光谱测定奶粉中蛋白质含量实时、快速,能满足工业过程分析中的测量精度要求,为提高奶粉质量分析水平提供了新的途径。     

敦煌辐射校正场反射辐射偏振特性研究

卫星遥感器辐射校正场的地表反射辐射测量(例如地表反射率、地表辐亮度等)对卫星遥感器的在轨定标至关重要。由于地物光谱仪自身具有一定的偏振敏感性, 场地反射辐射的偏振特性将会引入偏振测量误差。采用基于偏振成像仪和塔吊的非定点测量方式以及基于偏振光谱仪和BRDF测量架的定点测量方式, 测量了敦煌场490 nm和670 nm波段场地反射辐射的多角度偏振分布和局地偏振均匀性。试验结果表明, 敦煌辐射校正场的反射辐射具有一定的偏振特性。偏振特性和波段有关, 490 nm波段偏振度明显大于670 nm波段。490 nm和670 nm波段的多角度偏振分布关于太阳主平面对称。在太阳主平面内, 前向散射区偏振度大于后向散射区, 并随天顶角变大而变大。两种测量方式获得了一致的偏振特性分布规律。获得了直径100 m区域的场地反射辐射局部均匀性, 均匀性在6%左右。研究场地反射辐射的偏振特性对于场地辐射探测方案的改进以及辐射测量精度的提高具有重要意义。