Observation of nonequilibrium radiation behind strong shock waves in low-density air

Nonequilibrium radiation phenomena behind strong shock waves in low-density air are observed by using a couple of CCD camera systems in a shock tube experiment. The simultaneous observation for total radiation and its spectral radiation is carried out in order to elucidate spaced-ependent contribution of an individual radiation spectrum to the total radiation intensity. The results are shown for the shock velocity range from 9.0 km/s to 12.1 km/s at the initial pressure 13.3 Pa. Wavelength range is selected from 300 nm to 445 nm to investigate mainly the contributions from UV radiation. It is found that the band spectra due to the molecular species N₂⁺ and CN mainly contribute to the first-peak, while the spectra due to the atomic species O⁺ and N mainly contribute to the formation of the second-peak. It is also found that the Balmer series in H spectra strongly contributes to the second-peak. The radiation along the tube wall surfaces is composed of the same constituents as those around the tube axis as well as the spectra coming from the impurities.     

Continuous-wave 1.55 microm diode-pumped surface emitting semiconductor laser for broadband multiplex spectroscopy

A room-temperature-operating vertical external cavity surface emitting laser is applied around 1550 nm to intracavity laser absorption spectroscopy analyzed by time-resolved Fourier-transform interferometry. At an equivalent path length of 15 km, the high-resolution spectrum of the semiconductor disk laser emission covers 17 nm simultaneously. A noise-equivalent absorption coefficient at 1 s averaging equal to 1.5 x 10(-10) cm(-1)Hz(-1/2) per spectral element is reported for 65 km, the longest path length employed.     

高超声速再入试验的辐射光谱定量测量

利用膨胀管对宽度为45 mm和90 mm的半圆柱模型进行了地球再入高超声速流动试验,再入速度为8 km/s。试验利用配有ICCD相机的光谱仪,测量了具有空间分辨的激波后辐射光谱,光谱范围为250~550 nm,得到了沿流体方向的激波辐射轮廓线。分析发现在该光谱范围内辐射主要为CN(B-X)带系分子光谱。利用卤钨灯对该波段光谱进行定标,得到了激波层辐射的绝对辐射亮度。通过采用两种模型辐射亮度对模型宽度归一化后发现,绕流场高温气体辐射存在较强的自吸收现象,同时观测到了绕流场激波的三维效应。通过实验发现,CN(B-X)Δv=0带系的3-3振动带系385.2 nm波长位置和0-0带系388.4 nm波长位置辐亮度之比随着流场靠近模型边缘而逐渐下降,这表明激波层内辐射的动态非平衡特征。     

Brightness temperature of synchronic exoplanets measured by infrared photometry from the ground: Method and perspective

We explore a method to measure the temperature at the surface of “hot Jupiter” type exoplanets by relative photometry in the infrared at around 10 μm in N spectral band. The method is described and validated by numerical simulations. Thermal radiation from an exoplanet and its parent star are analysed. Geometrical configurations of extra-solar planet rotating synchronously around parent star are explored for a feasibility study of the detection. A Jupiter size planet in orbit at 0.025 astronomical unit from Sun-like parent star should have a harmonic signature of up to 0.2% in amplitude with a period of the planets orbital duration. Such a signature is difficult to detect when making absolute measurements, but by differential methods of analyses, and using a radiative transfer model to take into account background sky contribution of the Earth’s atmosphere, this relative accuracy can be reached. Some results of simulations of observation are also presented.     

Radiation gas dynamics of Martian space vehicles

The calculation data on convective and radiation heating of the Pathfinder space vehicle (SV) during entry into the Martian atmosphere at an angle of attack are presented. Comparison with the results of calculations of convective heating of the frontal surface of the Pathfinder SV in the axisymmetric statement is carried out. The data on the radiation heating of the Pathfinder SV entering the Martian atmosphere at an angle of attack have been obtained for the first time. The analysis of the spectral composition of the thermal radiation reaching the surface of the space vehicle is carried out; this makes it possible to mark the change of modes of the radiation heating.     

Characteristics of the spatial spectrum of plasma irregularities excited at mid-latitudes by the high-power “Sura” facility

We present the results of analysis of the spectra of amplitude scintillations at a frequency of 150 MHz and a difference phase at frequencies of 150 and 400 MHz, which were obtained in the experiment on radio tomography of artificial ionospheric turbulence (AIT) excited by the mid-latitude high-power “Sura” heating facility [1]. We used the data on radio probing of the AIT region at a frequency of 150 MHz by signals from artificial satellites in near-polar circular orbits at altitudes of 1000 km above the Earth’s surface. The signals were received simultaneously at three spaced apart points located at distances of about 100–150 km from each other along the projection of the satellite trajectory onto the Earth’s surface. The analysis of the data shows that in the range of scales smaller than 0.5–1.0 km across the geomagnetic field, the AIT spatial spectrum can be described by the power-law function with the spectral index p_⊥ = 1.7–2.5. For irregularities with the same transverse scales, the spectral index in the direction of the magnetic field amounts to p_‖ = 5–7. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 8, pp. 722–730, August 2007     

UV spectral measurements at moderately high resolution and of OH resonance scattering resolved by polarization during the MANTRA 2002-2004 stratospheric balloon flights

A moderately high-resolution (<0.1 nm) grating spectrometer designed to measure the solar radiation in the spectral range 295-315 nm was flown on the MANTRA stratospheric balloon payloads of 2002 and 2004. The instrument measures both the direct sunlight and the radiation scattered by the atmosphere. The latter can be observed in two orthogonal polarization directions, at 90° from the solar azimuth and at several elevations above the horizon. As the OH molecule is the principal resonant scatterer in this spectral region, this permits the inference of both ozone and OH column amounts as well as limited profile information. This paper describes the instrument and its in-flight characterization, the basic data processing and the influence of several aspects of the flight profile. The direct sun measurements are analyzed both to characterize the spectrometer responsivity to scattered radiation and to estimate the ozone abundance at the flight altitude and above. An example of a high-resolution solar spectrum at 37 km altitude is presented and compared with others in the literature. The measured OH and Rayleigh-scattered spectra are used to derive OH radiation intensity measurements (the OH airglow), which are compared with others in the literature.     

Spectral excess attenuation of monomode optical fibers with sinusoidally perturbed core radius

The spectral excess attenuation caused by coupling between the guided HE₁₁ mode and radiation modes is calculated with the aid of the formula derived by Marcuse for the radiation loss of a monomode optical fiber with step-index profile and sinusoidally perturbed core radius. The pronounced minima and maxima of the spectral excess attenuation curve converge as the spatial frequency of the perturbation of the core radius increases. Even perturbation amplitudes as small as 0.01 μm may lead to excess attenuations of the order of 10 dB/km if the radiation wavelength does not coincide with an attenuation minimum. The spectral behavior of the excess attenuation can be utilized to design fibers which act as optical filters.     

白铜热氧化过程中光谱发射率特性研究

随着科技的发展,工业领域对白铜产品质量的要求日益提升;利用辐射测温技术对白铜在冶炼和加工时的温度进行精确测量,是决定产品质量的重要手段,因此研究白铜的光谱发射率特性就显得尤为重要。基于傅里叶红外光谱仪搭建的光谱发射率测量装置,测量了白铜在四个温度点（673,773,873和973 K）,波长范围2～22 μm内的光谱发射率,分别研究了波长、温度、加热时间和氧化对白铜光谱发射率的影响。研究发现,在氮气环境下白铜的光谱发射率随温度的升高而增加,随波长的增加而减少。当白铜暴露在空气环境中,随着温度的升高,其光谱发射率迅速增加。673 K时,白铜表面生成一层细微的氧化物颗粒,阻止白铜进一步氧化,这些氧化物颗粒的光谱发射率大于白铜基底,所以此温度下短波处的光谱发射率略微增加。773 K时,白铜表面氧化物的主要成分是Cu₂O,在实验过程中也观察到白铜表面逐渐变红的现象,这也是白铜在773 K温度下其光谱发射率迅速增加的原因。873 K时,白铜表面氧化物的种类和含量明显增多,氧化膜的厚度满足干涉效应条件,在白铜的光谱发射率曲线中可以明显地观察到干涉极值的演变,随着加热时间的增加,干涉极值逐渐向长波移动。随着温度的升高,白铜的抗氧化能力下降。973 K时,白铜表面的氧化程度最深,在XRD图中氧化物的峰值也最大,因此氧化1 h后由于干涉效应产生的干涉极值数最多。综上所述,波长、温度和氧化对白铜的光谱发射率有重要的影响,在运用辐射测温技术测量白铜温度时应充分考虑上述因素的影响。该研究丰富了白铜的光谱发射率数据,为辐射测温提供了真实可靠的数据支撑。     

Controlling the radiation spectrum of quantum-well heterostructure lasers by ultrasonic strain

The radiation of a semiconductor laser has been modulated in frequency by variable strain. The strain is excited by injecting bulk or surface ultrasonic waves. Dynamic and static analyses of the variations in the spectral characteristics of the radiation in the presence of sound are performed. A model is suggested and the data obtained are analyzed theoretically. The radiation frequency modulation in InGaAsP/InP heterostructures produced by surface waves is shown to be determined mainly by the band gap modulation of the active region.     

A3铁、304钢和201钢光谱发射率

随着科学技术日新月异的发展,红外测量技术在遥感、辐射测温、红外隐身、农业、医疗等领域都展现出了重要的应用前景。在花样众多的辐射测量中,材料的发射率是重要的参数之一。为满足材料发射率数据的需求,根据一套自主研制的光谱发射率测量装置对A3铁、304钢以及201钢在不同温度下的光谱发射率进行了精确的测量,并对影响发射率的几个因素做了深入的探究。结果显示：这三种钢材的发射率随温度升高而变大,同等温度下A3铁的发射率要高于304钢和201钢,且材料中的铬含量会降低材料的发射率值。采用XRD分析了三种材料表面氧化后的成分,并探讨了表面成分变化对发射率的影响。结果表明：A3铁氧化后生成不稳定的四氧化三铁Fe₃O₄和氧化亚铁FeO,各种成分的相互转变会导致光谱发射率发生较大的变化,而304钢和201钢表面氧化后主要生成氧化铬,因而光谱发射率也相对比较稳定。另外使用辐射光叠加原理和Christiansen效应成功解释了三种材料的发射率在大约10 μm处出现极大值的现象。该研究极大地丰富了三种材料的光谱发射率数据,为辐射测量技术在三种材料中的应用提供了强有力的数据支撑。     

Acoustoelectronic interaction in InGaAsP/InP laser heterostructures

The dynamics of change in the spectral characteristics of the emission from a laser heterostructure due to an alternating strain induced by a surface acoustic wave is investigated. The spectral distributions of the laser radiation intensities are analyzed with the aim of elucidating the mechanisms responsible for the interactions occurring in the laser heterostructure. A model is proposed for describing the experimental data, and their theoretical analysis is performed. It is demonstrated that the acoustoelectronic interaction is dominant under the action of surface waves. The deviation of the observed frequency modulation of radiation is determined from a comparison of the theoretical calculations with experimental data.     

Influence of the Gaseous Medium on the Spectral Emission of Microplasma Obtained in Evaporating a Sample with the Aid of Laser Radiation

An investigation is made of the influence of air, oxigen, argon, and neon-helium atmosphere on the spatial distribution of the glow of microplasma, obtained in treating a brass sample with laser radiation and excited with the aid of a subsidiary synchronous discharge. The plasma's luminous zone, from which the spectral lines are recorded, extends when the inductance of the discharge circuit is lower and when an inert gaseous medium is used. The maxima of the intensities of the spectral lines with higher excitation energies appear at greater heights from the sample's surface.     

Internal distribution of radiation absorption in a semitransparent spherical particle

The internal distribution of spectral radiation absorption in a semitransparent spherical particle irradiated uniformly and isotropically is determined by the ray tracing method, and the detailed computation formulae for the internal spectral radiation absorption are deduced. The computed results show that the peak of internal volumetric spectral radiation absorption may locate at the interior shell of the particle. The dimensionless volumetric spectral radiation absorption is higher near the center for weakly absorbing or small spheres, but the dimensionless volumetric spectral radiation absorption is higher near the surface for strongly absorbing or large spheres. The corresponding physical interpretations of the internal spectral absorption distribution are given.     

Spectral emissivity modeling of steel 201 during the growth of oxidation film over the temperature range from 800 to 1100 K in air

This study explores the spectral emissivity modeling of steel 201 during the growth of oxidation film over the temperature range from 800 to 1100 K at 1.5 μm. The radiance coming from the specimen is received by an InGaAs photodiode detector. The specimen temperature is obtained by averaging the two platinum–rhodium thermocouples, which are tightly welded in the front surface of specimen near the measuring area viewed by the detector. The variation of spectral emissivity with the temperature is studied at a given heating time. The variation of spectral emissivity with the heating time is evaluated at a definite temperature. The strong oscillations of spectral emissivity are observed and discussed in detail, which originate from the interference effect between the radiation stemming from the oxidization film on the specimen surface and the radiation coming from the specimen surface. The measurement uncertainties of spectral emissivity contributed only by the surface oxidization are about 3.2–14.1%. At a given heating time, the variation of spectral emissivity with the temperature abides well by a simple analytic functional form. And at a definite temperature, the variation of spectral emissivity with the heating time can also be well reproduced by fitting except for the periodical oscillations.     

基于地面试验的嫦娥五号月球矿物光谱分析仪数据质量分析

探月工程三期项目将完成“绕、落、回”三个阶段中的采样返回任务,将在未来发射嫦娥五号(CE-5)探测器,执行月面着陆、采样并返回地球的任务。嫦娥五号月球矿物光谱分析仪(LMS)是探月工程三期重要的数据来源,通过LMS光谱数据分析识别月球表面物质的矿物组成,包括含水矿物,同时有助于判断岩石类型,辅助地层学分析。为月球的形成过程、月球地质演变及岩石-水交互作用的研究提供数据支撑。相比于嫦娥三号红外成像光谱仪,LMS将光谱范围从450～2 400 nm扩展到了480～3 200 nm,除了能探测月球表面主要矿物辉石、橄榄石等,还可以探测3 000 nm附近的羟基吸收峰特征,为月球表面是否存在“水”提供强有力的证据。此外,嫦娥五号月面工作任务将获取月表以下物质,LMS可以对月表采样前后的采样区域进行光谱探测,比较不同深度、不同风化程度下的月壤光谱特征,且与后期返回样品的实验室光谱对比分析。为保证LMS月面数据的可靠性,在探测器发射之前开展了LMS地面验证试验,采用多种矿物及矿物混合样品,在不同试验环境下获取LMS的探测数据,分析研究LMS的矿物成分探测能力,并结合标准比对仪器光谱进行光谱质量分析。计算了所有实验样品的光谱不确定度参数。除了具有低反射率的钛铁矿外,所有样品都具有高质量的光谱数据。同时,在相同条件下,LMS光谱特征与标准比对仪器得到的光谱数据相一致,表明LMS整体数据质量高。     

Pump-depleting four-wave mixing in supercontinuum-generating microstructure fibers

Four-wave mixing processes are shown to provide a high efficiency of non-linear optical frequency conversion and spectral transformation of ultrashort pulses in supercontinuum-generating microstructure fibers. Pump-depleting conversion of 800-nm radiation to the spectral range around 500 nm is achieved by phase-matching the parametric four-wave mixing process for 80-fs Ti:sapphire-laser pulses. The ways to use microstructure fibers for generating frequency-tunable radiation through four-wave mixing with the maximum efficiency of pump-field frequency conversion are discussed. PACS 42.65.Wi; 42.81.Qb     

Determination of true temperature of opaque materials via spectral distribution of thermal radiation intensity: application of Wien’s displacement law

The equation for the derivative connecting surface spectral emissivity, wavelength, and thermodynamic (true) temperature of an opaque heated body at the point of spectral maximum of thermal radiation was obtained. It is suggested to solve the problem of determining the true temperature of an opaque surface in two stages. At the first stage, the spectral range, most comfortable for approximation of body emissivity, is distinguished using a special function (relative emissivity), and the true temperature is determined. At the second stage, the true temperature is determined again using the resulting equation for the derivative. The dimensionless parameter that connects the radiative properties of material with the peak wavelength and characterizes deviation from Wien’s displacement law was found. If the absolute value of this parameter is low, the value of true temperature obtained at the first step can be specified at the second stage. This approach is illustrated by experimental data obtained at comparison of spectral radiance of the temperature lamps.     

Reconstruction of time-averaged temperature of non-axisymmetric turbulent unconfined sooting flame by inverse radiation analysis

A multi-wavelength inversion method is extended to reconstruct the time-averaged temperature distribution in non-axisymmetric turbulent unconfined sooting flame by the multi-wavelength measured data of low time-resolution outgoing emission and transmission radiation intensities. Gaussian, β and uniform distribution probability density functions (PDF) are used to simulate the turbulent fluctuation of temperature, respectively. The reconstruction of time-averaged temperature consists of three steps. First, the time-averaged spectral absorption coefficient is retrieved from the time-averaged transmissivity data by an algebraic reconstruction technique. Then, the time-averaged blackbody spectral radiation intensity is estimated from the outgoing spectral emission radiation intensities. Finally, the time-averaged temperature is approximately reconstructed from the multi-wavelength time-averaged spectral emission radiation data by the least-squares method. Noisy input data have been used to test the performance of the proposed inversion method. The results show that the time-averaged temperature distribution can be estimated with good accuracy, even with noisy input data. The accuracy of the estimation decreases with the increase of turbulent fluctuation intensity of temperature and the effects of assumed PDF on the reconstruction of temperature are small.     

影响光谱辐亮度标定因素的分析

在利用漫反射板标定光谱辐亮度的实验装置中,标准灯完全可以近似为点光源。通过对进入光谱仪的辐射通量的数值积分,可以对应求出仪器的实测光谱辐亮度的计算公式。计算表明,实测光谱辐亮度并不等于漫反射板表面的光谱辐亮度,而有一个随标定条件变化的微小差值。通过计算,对光谱仪与漫反射板的距离、光谱仪入射挟缝的光轴与漫反射板法线的夹角以及标准灯与漫反射板的距离等影响光谱仪标定的因素进行分析,得到了最佳的标定条件。讨论了理想标定情况、光谱仪视场趋于一点的极限情况和采用实际的双向反射分布函数已知的漫反射板标定时,实测光谱辐亮度的计算情况。