新型超光谱大气CO2遥感探测技术

论述了空间外差光谱技术在大气CO2超光谱遥感探测中的应用。分析了高精度大气CO2遥感探测所需的光谱波段、光谱分辨率以及信噪比等重要指标,以此为设计依据,开展了大气CO2空间外差光谱仪核心元器件指标的计算。利用 Y-12飞机进行航空验证实验,分别采集了农田、工业区、沙滩区域的 CO2吸收光谱数据,并开展了数据处理,获取了机载平台下的CO2精细吸收谱线。初步的反演结果表明空间外差光谱技术能够满足大气CO2等温室气体的遥感探测灵敏度要求。     

空间外差光谱技术仿真研究

针对空间外差光谱技术(SHS)仿真研究,本文介绍了不同特征光谱光源的仿真计算.根据空间外差光谱仪的基本原理和系统结构特点,以及SHS系统参数与光谱干涉的调制关系,分别对单色光谱、连续光谱进行了理论仿真探讨,并且分析了不同带宽和采样间隔对仿真结果的影响.此外,采用空间外差光谱仪实验台装置获取实测数据,并与仿真结果进行对比分析.实验结果表明理论仿真数据和实测数据能够很好的吻合,能够为实际工作提供有益的参考,同时为SHS系统的设计和改造提供必要的依据.     

一种交叉的切尔尼-特纳型远紫外成像光谱仪

本文介绍了远紫外成像光谱仪的需求和若干关键技术,描述了一种光谱范围为100～300nm,光谱分辨率优于1.67mm的远紫外波段成像光谱仪的设计方法和定标实验.该仪器基于交叉的切尔尼-特纳型光谱仪光路结构,采用全反射式系统.根据初级像差理论设计了光学系统,使用Zemax进行了仿真和优化,在紫外-可见光波段对仪器的性能进行实验验证,并进行了光谱定标和成像性能分析.     

高光谱分辨率近红外CO2成像光谱仪设计与模拟

为满足大气CO2吸收光谱测量的要求,基于成像光谱仪基本工作原理和光学设计理论,设计了一种近红外CO2吸收光谱高光谱分辨率成像光谱仪.它采用简单平面反射光栅光谱仪结构,由入缝、两片聚焦透镜、平面反射光栅及两片成像透镜组成.透镜材料为普通常用光学玻璃,为减化系统结构透镜采用了二次非球面设计.采用ZEMAX软件对近红外光谱仪的光学系统进行了优化设计与模拟分析.最终设计与模拟分析结果表明,该光学系统光谱范围为1 591～1 621 nm,分辨率＜0.08 nm,F数为1.8,满足设计要求.     

微型紫外光纤光谱仪的光学系统设计及性能检测

采用非对称交叉的切尼尔-特纳(C-T)光路结构,设计了一种微型紫外光纤光谱仪的光学系统.用ZEMAX对光路进行仿真、像质评价和优化,对各类像差进行校正.同时,对不同狭缝尺寸和光栅常数的光谱仪理论分辨率进行了分析.当采用30μm狭缝和1 800线/mm光栅时,模拟光学系统在180~270nm光谱范围内整体分辨率优于0.5nm,在180nm附近最高分辨率达到0.1nm.最后,基于该光学设计研制了一台光谱仪样机,在使用交流电弧激发金属纯铁样品的条件下,对原子发射光谱进行了检测.     

一种微型光纤光谱仪的研制及其性能测试

报道了一种自行研制的微型光纤光谱仪及其性能测试结果.基于C-T(czerny-turner)成像系统,将通过光纤导入的待测光进行分光后成像于线阵CCD(charge-coupled device)探测器上.采用FPGA(field-pro-grammable gate array)作为主处理器实现CCD的驱动、数据采集与处理,通过USB 2.0接口将数据传送至上位机.根据USB的接口协议及数据格式,编写了一套光谱仪测试软件.利用汞灯作为测试光源,对自制的光纤光谱仪性能进行了仔细分析.结果表明,当采用缝宽为30μm的狭缝时,仪器的波长准确度小于0.3nm,光谱分辨率可达1.1nm.     

零级像无缝光谱仪波长定标方法研究

无缝光谱仪结构简单且可靠性高,在空间天文低分辨率光谱观测中普遍应用,但它通常无光谱定标设备并面临光谱定标难的问题。依据空间无缝光谱仪零级像和光谱像同时存在的特点,可采用基于零级像的无缝光谱实现定标。首先根据无缝光谱仪工作原理分析影响定标结果的各参数之间的关系;其次通过改进高斯拟合算法,拟合出更精确的光斑中心坐标;然后搭建无缝光谱仪仿真光路,将神经网络用于定标过程中的波长预测,并训练相关数据;最后测试并验证神经网络在波长预测中的准确性。经模拟该方法的波长预测结果误差小于1nm,定标精度好于其他传统方法,从而证明基于零级像的波长定标方法的可行性。     

高光谱成像与应用技术发展

介绍了高光谱成像的需求与应用、光谱成像技术的现状与发展。高光谱成像已在产品分选、精准农业、环境监测、文物保护、刑事侦查、伪装识别等行业得到应用。传统的棱镜光栅色散型、连续可调谐滤光型、傅里叶变换干涉型等光谱成像分光方式成本高、体积大、速度慢,目前其光谱成像仪仍作为主要的研究设备。为促进产业化应用,需要发展体积小、成本低、速度快的光谱成像技术。计算层析、压缩编码、胶体量子点CQDs光谱成像技术仍需理论突破,短时间难以实用。积分视场、离散采样光谱成像技术原理简单、技术成熟,可用于空间分辨率要求不高的场合。复眼滤光式、像素滤光式光谱成像技术通过单片集成像素级滤光片,既能在权衡光谱分辨率与空间分辨率的基础上实现实时性,又能极大地减小体积、降低成本。     

同步测量海水固有光学特性的高光谱剖面仪样机设计

基于双光路原理,研制出一种同步测量海水固有光学特性的高光谱剖面仪样机.样机用全反射管作测量吸收系数的样品池,全吸收管作测量衰减系数的样品池.使用高灵敏度的电荷耦合器(CCD)做光纤单色仪的光电探测器件,样机的光谱分辨率达到1.64nm.CCD信号的积分时间由复杂可编程逻辑器件(CPLD)和可编程计数器自动调整.用PC104微机自动控制数据采集和数据存储.存储数据由无线通信器件下载.室内实验验证了仪器测量的稳定性和可靠性.     

多角度测量系统实现室外BRDF测量

为了实现室外BRDF的准确测量,设计了多角度测量系统.测量系统包括一台自动测量架和两台ASD(Analytical Spectral Devices)公司生产的野外型光谱仪,光谱仪的光谱分辨率为3nm,一台光谱仪固定在测量架平台上测量目标各方向反射,另一台光谱仪放置在地面上同时测量漫反射板反射.应用该系统进行了室外草地的测量实验,测量整个周期(66个方向点)用时10min,测量主平面(间隔5°,共31个方向点)用时2.5min.测量结果显示目标的反射为非朗伯性,并在主平面的反射方向性最强烈.     

OH absorption spectroscopy in a flame using spatial heterodyne spectroscopy

We demonstrate measurements of OH absorption spectra in the post-flame zone of a McKenna burner using spatial heterodyne spectroscopy (SHS). SHS permits high-resolution, high-throughput measurements. In this case the spectra span approximately 308-310 nm with a resolution of 0.03 nm, even though an extended source (extent of approximately 2x10(-7) m(2) rad(2)) was used. The high spectral resolution is important for interpreting spectra when multiple absorbers are present for inferring accurate gas temperatures from measured spectra and for monitoring weak absorbers. The present measurement paves the way for absorption spectroscopy by SHS in practical combustion devices, such as reciprocating and gas-turbine engines.     

Raman spectroscopy using a spatial heterodyne spectrometer: proof of concept

The use of a spatial heterodyne interferometer-based spectrometer (SHS) for Raman spectroscopy is described. The motivation for this work is to develop a small, rugged, high-resolution ultraviolet (UV) Raman spectrometer that is compatible with pulsed laser sources and that is suitable for planetary space missions. UV Raman is a particular technical challenge for space applications because dispersive (grating) approaches require large spectrographs and very narrow slits to achieve the spectral resolution required to maximize the potential of Raman spectroscopy. The heterodyne approach of the SHS has only a weak coupling of resolution and throughput, so a high-resolution UV SHS can both be small and employ a wide slit to maximize throughput. The SHS measures all optical path differences in its interferogram simultaneously with a detector array, so the technique is compatible with gated detection using pulsed lasers, important to reject ambient background and mitigate fluorescence (already low in the UV) that might be encountered on a planetary surface where samples are uncontrolled. The SHS has no moving parts, and as the spectrum is heterodyned around the laser wavelength, it is particularly suitable for Raman measurements. In this preliminary report we demonstrate the ability to measure visible wavelength Raman spectra of liquid and solid materials using an SHS Raman spectrometer and a visible laser. Spectral resolution and bandpass are also discussed. Separation of anti-Stokes and Stokes Raman bands is demonstrated using two different approaches. Finally spectral bandpass doubling is demonstrated by forming an interference pattern in both directions on the ICCD detector followed by analysis using a two-dimensional Fourier transform.     

HL-2A托卡马克装置CXRS光学系统设计

电荷交换复合谱(CXRS)是一项先进的测量托卡马克等离子体温度及空间分布的方法。针对我国HL-2A托卡马克装置上CXRS光谱采集系统对宽光谱范围(470?660nm)、大视场(535.34mm)、宽光束(直径110mm)、高空间分辨(14道)以及与后续导光光纤数值孔径(0.22)匹配等要求,应用ZEMAX光学设计软件优化设计了一片反射镜与四片透镜组合的光学系统,并通过将像面倾斜的方法进一步减小了像差。模拟计算表明像面最大弥散斑RMS半径为88.14?m,像方数值孔径0.217,很好地满足了使用需要。     

Linear variable optical filter-based ultraviolet microspectrometer

An IC-compatible linear variable optical filter (LVOF) for application in the UV spectral range between 310 and 400 nm has been fabricated using resist reflow and an optimized dry-etching. The LVOF is mounted on the top of a commercially available CMOS camera to result in a UV microspectrometer. A special calibration technique has been employed that is based on an initial spectral measurement on a xenon lamp. The image recorded on the camera during calibration is used in a signal processing algorithm to reconstruct the spectrum of the mercury lamp and the calibration data is subsequently used in UV spectral measurements. Experiments on a fabricated LVOF-based microspectrometer with this calibration approach implemented reveal a spectral resolution of 0.5 nm.     

Measurement of ultrasonic pressure by heterodyne interferometry with a fiber-tip sensor

A fiber-optic measurement system is described that allows ultrasound to be detected in fluids. It is based on a heterodyne interferometer, and the sensing element consists of a metal-coated fiber tip. The heterodyne technique permits direct acquisition of the sound pressure. The required ac photodetection is carried out with wide bandwidth, and the system provides high temporal and spatial resolution. For optimum performance the system parameters are matched to the sound-wave properties of the current application with the aid of theoretical and numerical calculations. The fiber-optic sensor system was applied to two problems of ultrasonic exposimetry in which the favorable features of the measurement technique were exploited. Shock waves from an electromagnetic lithotripter were investigated by use of the wide bandwidth of the system, and the subharmonic in an ultrasonic cleaner was detected, which indicates cavitation.     

Submicrosecond speed optical coherence tomography system design and analysis by use of acousto-optics

A novel high-speed no-moving-parts optical coherence tomography (OCT) system is introduced that acquires sample data at less than a microsecond per data point sampling rate. The basic principle of the proposed OCT system relies on use of an acousto-optic deflector. This OCT system has the attractive features of an acousto-optic scanning heterodyne interferometer coupled with an acousto-optic (AO) variable optical delay line operating in a reflective mode. Fundamentally, OCT systems use a broadband light source for high axial resolution inside the sample or living tissue under examination. Inherently, AO devices are Bragg-mode wavelength-sensitive elements. We identify that two beams generated by a Bragg cell naturally have unbalanced and inverse spectrums with respect to each other. This mismatch in spectrums in turn violates the ideal autocorrelation condition for a high signal-to-noise ratio broadband interferometric sensor such as OCT. We solve this fundamental limitation of Bragg cell use for OCT by deploying a new interferometric architecture where the two interfering beams have the same power spectral profile over the bandwidth of the broadband source. With the proposed AO based system, high (e.g., megahertz) intermediate frequency can be generated for low 1/f noise heterodyne detection. System issues such as resolution, number of axial scans, and delay-path selection time are addressed. Experiments described demonstrate our high-speed acousto-optically tuned OCT system where optical delay lines can be selected at submicrosecond speeds.     

Two-dimensional imaging of soot volume fraction in laminar diffusion flames

A technique for acquiring two-dimensional soot-volume-fraction measurements in laminar flames has been demonstrated. The technique provides a map of very low noise concentration over a range of wavelengths (250-1100 nm). A noise level of 0.0007 in extinction and a spatial resolution of 30-40 mum for soot concentration were achieved with an arc lamp source that was filtered to provide greater spatial coherence and a CCD detector. The broadband arc lamp source also allowed us to avoid the added noise resulting from speckle with coherent laser sources. Beam steering, due to refractive-index gradients in the flame, was measured and compared with theoretical predictions. The optical arrangement to minimize the effect of beam steering is described. As a result the beam steering had no effect on the soot measurements in the flames examined. Flame-transmission maps obtained with this system in an ethylene/air laminar diffusion flame are presented. Tomographic analysis from use of an Abel inversion of the line-of-sight data to obtain radial profiles of soot concentration is described.     

Transmission-type angle deviation microscopy

We present a new microscopy technique that we call transmission angle deviation microscopy (TADM). It is based on common-path heterodyne interferometry and geometrical optics. An ultrahigh sensitivity surface plasmon resonance (SPR) angular sensor is used to expand dynamic measurement ranges and to improve the axial resolution in three-dimensional optical microscopy. When transmitted light is incident upon a specimen, the beam converges or diverges because of refractive and/or surface height variations. Advantages include high axial resolution (approximately 32 nm), nondestructive and noncontact measurement, and larger measurement ranges (+/- 80 microm) for a numerical aperture of 0.21 in a transparent measurement medium. The technique can be used without conductivity and pretreatment.