High-Resolution Broadband Millimeter-Wave Astrophysical Spectrometer with Triple Product Acousto-Optical Processor

An advanced conceptual design of a high-bit-rate triple product acousto-optical processor is presented that can be applied in a number of astrophysical problems. We briefly describe the Large Millimeter Telescope as one of the potential observational infrastructures where the acousto-optical spectrometer can be successfully used. A summary on the study of molecular gas in relatively old (age > 10 Myr) disks around main sequence stars is provided. We have identified this as one of the science cases in which the proposed processor can have a big impact. Then we put forward triple product acousto-optical processor is able to realize algorithm of the space-and-time integrating, which is desirable for a wideband spectrum analysis of radio-wave signals with an improved resolution providing the resolution power of about 105 - 106. It includes 1D-acousto-optic cells as the input devices for a 2D-optical data processing. The importance of this algorithm is based on exploiting the chirp Z-transform technique providing a 2D-Fourier transform of the input signals. The system produces the folded spectrum, accumulating advantages of both space and time integrating. Its frequency bandwidth is practically equal to the bandwidth of transducers inherent in acousto-optical cells. Then, similar processor is able to provide really high frequency resolution, which is practically equal to the reciprocal of the CCD-matrix photo-detector integration time. Here, the current state of developing the triple product acousto-optical processor in frames of the astrophysical instrumentation is shortly discussed.

Optical Spectrometer with Acousto-Optical Dynamic Grating for Guillermo Haro Astrophysical Observatory

Optical spectrometer of the Guillermo Haro astrophysical observatory (Mexico) realizes investigations in the visible and near-infrared range 350 - 800 nm and exploits mechanically removable traditional static diffraction gratings as dispersive elements. There is a set of the static gratings with slit-densities 150 - 600 lines/mm and optical apertures 9 cm × 9 cm that provide the first order spectral resolution from 0.8 to 3.2 A/pixel, respectively. However, the needed mechanical manipulations, namely, replacing the static diffraction gratings with various resolutions and following recalibration of spectrometer within studying even the same object are practically inconvenient and lead to wasting rather expensive observation time. We suggest exploiting an acousto-optical cell, i.e. the dynamic diffraction grating tunable electronically, as dispersive element in that spectrometer. Involving the acousto-optical technique, which can potentially provide electronic control over the spectral resolution and the range of observations, leads to eliminating the abovementioned demerits and improving the efficiency of analysis.

Ultra compact and high resolution spectrometer based on optical transmission through submicron interferometer array

We present an ultra compact and high resolution free space optical spectrometer and demonstrate it by using FDTD simulations. The miniature interferometer-based spectrometer is a series of submicron phase objects on a polymethyl methacrylate(PMMA) film with a CCD as the detector. The spectrum is obtained by solving a system of simultaneous linear equations. The Tikhonov regularization method is used to achieve a resolution at the picometer level. Compared with conventional spectrometers, the proposed device is low-cost and easy to fabricate due to its simple structure. Furthermore, its compact feature renders the device ideal for miniaturization and integration as the systems in microfluidics architectures and lab-on-chip designs.

Mid-infrared Optical Frequency Comb-based Fourier Transform Spectrometer for Broadband Molecular Spectroscopy

Optical frequency combbased Fourier transform spectroscopy has the features of broad spectral bandwidth,high sensitivity,andmultiplexed trace gas detection,which has valuable application potential in the fields of precision spectroscopy and trace gas detection.Here,we report the development of a mid-infrared Fourier transform spectrometer based on an optical frequency comb combined with a Herriott-type multipass cell.Using this instrument,the broadband absorption spectra of several important molecules,including methane,acetylene,water molecules and nitrous oxide,are measured by near real-time data acquisition in the 2800-3500 cm^(-1)spectral region.The achieved minimum detectable absorption of the instrument is 4.4×10^(-8)cm^(-1)·Hz^(-1/2)per spectral element.Broadband spectra of H_(2)0 are fited using the Voigt profile multispectral fitting technique and the consistency of the concentration inversion is 1%.Our system also enables precise spectroscopic measurements,and it allows the determination of the spectral line positions and upper state constants of N_(2)O in the(0002)-(1000)band,with results in good agreement with those reported by Toth[Appl.Opt.30,5289(1991)].

Effects of optical axis direction on optical path difference and lateral displacement of Savart polariscope

A simple method is applied to calculating the optical path difference （OPD） of a plane parallel uniaxial plate with an arbitrary optical axis direction. Then, the theoretical expressions of the OPD and lateral displacement （LD） of Savart polariscope under non-ideal conditions are obtained exactly. The variations of OPD and LD are simulated, and some important conclusions are obtained when the optical axis directions have an identical tolerance of ／pm 1^{{／circ}}. An application example is given that the tolerances of optical axis directions are gained according to the spectral resolution tolerances of the stationary polarization interference imaging spectrometer （SPIIS）. Several approximate formulae are obtained for explaining some conclusions above. The work provides a theoretical guidance for the optic design, crystal processing, installation and debugging, data analysis and spectral reconstruction of the SPIIS.

Low-cost spectrometer design for ultra-high resolution spectral domain optical coherence tomography

In this Letter,we present a low-cost,high-resolution spectrometer design for ultra-high resolution optical coherence tomography(UHR-OCT),in which multiple standard achromatic lenses are combined to replace the expensive F-theta lens to achieve a comparable performance.For UHR-OCT,the spectrometer plays an important role in high-quality 3D image reconstruction.Typically,an F-theta lens is used in spectrometers as the Fourier lens to focus the dispersed light on the sensor array,and this F-theta lens is one of the most expensive components in spectrometers.The advantage of F-theta lens over the most widely used achromatic lens is that the aberrations(mainly spherical aberration,SA)are corrected,so the foci of the dispersed optical beams(at different wavelengths)with different incident angles could be placed on the sensor array simultaneously.For the achromatic lens,the foci of the center part of the spectrum are farther than those on the side in the longitudinal direction,causing degradations of the spectral resolution.Furthermore,in comparison with the achromatic lens with the same focal length,those with smaller diameters have stronger SA,but small lenses are what we need for making spectrometers compact and stable.In this work,we propose a simple method of using multiple long-focal-length achromatic lenses together to replace the F-theta lens,which is>8-fold cheaper based on the price of optical components from Thorlabs,US.Both simulations and in vivo experiments were implemented to demonstrate the performance of the proposed method.

Refractive index characteristics of edible oils based on spectrometry and effects of oil dispersion on OCT

It is necessary to investigate the wavelength-dependent variation rules of the refractive index of edible oils so as to explore the specificity of the dispersion in light propagation,imaging,and interference processes among different types of edible oil products.In this study,by deriving the refractive index equations of the double glass sheet holding device and oil,the reflectance spectra of three different types of oil samples,namely,peanut oil,colza oil,and kitchen waste oil,were measured via a spectrometer.Furthermore,the refractive index model of these different types of oil samples was investigated.Additionally,based on the oil dispersion characteristics,the dis-persion of oil in optical coherence tomography(OCT)was compensated via deconvolution.In the wavelength range of λ∈(380,1500)nm,the analytical expressions of the double glass sheet holding device and oils are featured by practical reliability.The refractive indexes of three different types of oils n∈(1.38,1.52)show normal dispersion characteristics.The Cauchy co-efficient matrix of the oil refractive index can be used for oil identification;in particular,the healthy oil and waste oil differ significantly in terms of the Cauchy coefficient matrix in the infrared band.Oil dispersion has almost no influence on the phase spectra of oils but can enhance their amplitude spectra.The dispersion mismatch can be eliminated by calculating the convo-lution kernel.The envelope broadening factors of OCT interference signals of oil products are 0.84,0.64,and 0.91,respectively.According to the present research results,the refractive index model of oil can effectively remove the influence of the holding device.The refractive indexes of three different types of oil samples show similar wavelength-dependent variation characteristics,which confirms the existence of many correlated components in these oil samples.The established refractive index model of oil in a wide spectral range,from the ultraviolet to the infrared band,can be adequately employed for identifying different types of oils.The numerical dispersion compensation based on the established refractive index model can enhance the axial resolution in OCT imaging.

Miniaturized short-wavelength infrared spectrometer for diffuse light applications

A miniaturized short-wavelength infrared spectrometer for use with diffuse light was created by combining a thin form factor carbon nanotube composite collimator,a linear variable filter,and an InGaAs photodiode array.The resulting spectrometer measures 3 mm×4 mm×14 mm and shows a significant improvement in resolution over a spectrometer without the collimator when used with diffuse light.Its small size and high throughput make it ideal for applications such as wearable optical sensing,where light from highly scattering tissue is measured.Plethysmographic measurements on the wrist were demonstrated,showing rapid data collection with diffuse light.

紫外小F数高变倍高光谱成像仪设计

常规成像光谱仪一般变倍比较低,不利于大视场长狭缝多通道光学系统的扩展应用,此外,空间遥感中紫外波段的辐射能量较低,需要成像光谱仪具有更小的F数。针对高光谱分辨率成像光谱仪小F数的探测需求,本文设计了一种具有高变倍的高光谱分辨率Offner紫外成像光谱仪。该成像光谱仪的后置分光系统采用了具有轻小型特点的改进型Offner结构。结合成像光谱仪对变倍比和小F数的需求,通过理论推导得到Offner初始结构参数。在像面前插入一块弯月透镜,增加系统的优化自由度,进而提升系统的成像质量。最终得到的成像光谱仪工作在270~300 nm波段时,具有40 mm的长狭缝,光谱分辨率优于0.6 nm,系统变倍比小于0.22,F数小于2,在截止频率为14 lp/mm时,系统调制传递函数(MTF)均优于0.9,系统各波段各视场均方根半径(RMS)均小于12μm。本文的研究对紫外波段高光谱探测成像光谱仪实现小F数、高变倍设计提供了一种设计方案。

亚角秒空间分辨的太阳极紫外宽波段成像光谱仪光学设计

狭缝式成像光谱仪是太阳极紫外光谱成像探测的重要工具之一,然而目前国内尚无该类载荷,导致太阳物理学和空间天气学等学科在极紫外光谱诊断研究方面主要依赖国外仪器数据,严重制约了相关学科的发展.国外已发射的成像光谱仪仅具有2"量级的空间分辨率,很难观测到日冕加热模型预测的等离子体核心特征.为了更好地理解太阳不同层次大气之间的耦合过程,需要更宽光谱覆盖的太阳观测数据.鉴于此,本文提出并设计了一款亚角秒空间分辨的太阳极紫外宽波段成像光谱仪,相比现有仪器,系统能够实现更高空间和光谱分辨率、更宽光谱范围覆盖的观测.性能评价结果表明,系统在62—80 nm,92—110 nm波段内的像元空间分辨率均优于0.4",光谱分辨率均优于0.007 nm,光谱成像质量接近衍射极限,对我国未来首台空间太阳极紫外成像光谱仪的研制具有重要参考价值.

手性分子构象分析装置圆二色光谱仪的加强与改造

圆二色光谱仪是对手性分子进行构象分析和理化性质表征的重要仪器.然而长期高强度的使用会产生光谱仪光学元件劣化、检测器灵敏度降低等问题.通过优化分光系统的光学元件提升光传输效率,升级具有更高量子效率的大面积雪崩硅光电二极管检测器,进而大幅提高仪器信噪比,同时将测量波长范围从175~900 nm扩展到175~1150 nm.在氙灯被点燃之前用氮气彻底净化仪器,把氧气排除在光谱仪之外是非常重要的操作步骤.安装具有监视、计划、流量设置、报警和辅助控制等功能的活性氮监测系统,可以实时监测控制仪器内部氮气吹扫情况.通过升级改造,既加强了仪器的性能,又节省了氮气消耗成本,同时仪器使用寿命将进一步延长.

痕量气体掩星探测高光谱成像光谱仪光学系统设计

痕量气体作为大气的重要成份,对地球的生态起着重要作用。为了实现宽波段、高光谱全天时连续测量,本文设计了一款在掩星探测模式下工作的高光谱成像光谱仪。该系统为共狭缝的双通道结构,紫外-可见光通道采用单凹面光栅结构、红外通道采用利特罗与浸没光栅结合结构,有效地减小了体积。利用软件对光学结构进行优化,优化结果表明:光谱仪在250~952 nm波段范围内工作,其中紫外-可见光通道工作波段为250~675 nm、光谱分辨率优于1 nm、MTF在奈奎斯特频率为20 lp/mm处均高于0.58、全视场各波长处RMS值均小于21μm;红外通道工作波段为756~952 nm、光谱分辨率优于0.2 nm、MTF在奈奎斯特频率为20 lp/mm处均高于0.76、全视场各波长处RMS值均小于6μm,均满足设计要求。结果表明该高光谱成像光谱仪系统可以实现对痕量气体的掩星探测。

基于PSIM机载大视场宽谱段偏振光谱成像系统光学设计

为满足偏振光谱成像探测中对于大视场、宽谱段技术要求,设计了一种基于偏振强度调制技术(PSIM)的宽谱段大视场偏振光谱成像仪。针对前置望远镜组,文中对现有国内玻璃材料消色差分析,优选了可见至短波红外的复消色差玻璃,通过控制镜组中PSIM模块光线角度,实现大视场内在PSIM模块上的入射角度需求。结合分析结果,采用光学设计软件优化设计。设计结果表明,前置望远系统能够实现波段为400~1 700 nm,视场角为72°,焦距为20 mm, F数为4的高质量成像,全谱段内探测器截止频率处传递函数优于0.4, PSIM模块上最大入射角度为±4.99°,有效保证了各视场内偏振调制的一致性。后置光谱分光系统采用基于Offner结构的凸面光栅,优化结果显示各波段点列图均小于一个像元,在探测器奈奎斯特频率处中心波长的MTF达到0.6,各项指标均满足设计要求。本文对于基于PSIM宽谱段偏振光谱成像仪器的工程化具有很重要的现实意义,对宽谱段光学系统消色差设计也具有一定指导意义。

星载高动态范围差分吸收成像光谱仪成像电路设计及实现

星载差分吸收成像光谱仪通常运行于太阳同步轨道,探测地表反射光的光谱并根据特征气体的谱线吸收强度测量区域内某些痕量气体浓度。第一代星载差分吸收光谱仪受限于探测器性能等原因,探测的动态范围不大,造成暗背景下数据信噪比低,亮背景下像元饱和。随着更大阱深,更高速度的探测器出现,第二代高动态范围的差分吸收成像光谱仪得以实现。本文介绍了高动态范围的差分吸收光谱仪成像电路的研制过程,包括器件选型,电路方案及电路测试,并对测试结果进行了分析。重点讨论了高动态范围的实现,给出了单点测量值的概念,提出了最大单点测量值的计算公式,解释了最大单点测量值与动态范围的关系,并评估了探测器件的单点探测能力,同时规划了未来进一步提高动态范围的方法,从而为同类设备的研制提供参考。

适用于无人机搭载的轻小型成像光谱仪光学系统设计

设计了一种适用于无人机搭载的轻小型成像光谱仪(Light and compact imaging spectrometer,LCIS)光学系统。该光学系统的工作波段覆盖400~1000 nm,F数为3.3,视场大小为11°,光谱分辨率优于3 nm。采用Zemax对该光学系统进行仿真和优化,优化结果表明,点列图均方根(RMS)半径最大值为4.221μm,小于单个像元尺寸的一半,谱线弯曲最大值为1.30μm,色畸变最大值为1.16μm,分别占像元尺寸的8.69%和7.73%,在33 lp/mm处的调制传递函数(MTF)值优于0.7,各项指标评价结果均表明该光学系统具有较好的成像质量。此外,该光学系统体积为190 mm×160 mm×90 mm,表明该系统不仅光谱分辨率高、成像质量好,还具有体积小、结构紧凑的优点。本研究为轻小型成像光谱仪的研制提供了核心技术支持,为基于无人机搭载成像光谱仪开展遥感器在轨辐射定标工作奠定了基础。

“工程光学”傅里叶变换光谱仪实验设计

“工程光学”是测控技术与仪器等专业重要的专业课程,该课程理论性较强,学生往往对课程涉及的物理原理认识不够深刻,难以应用到实践当中。通过设计傅里叶变换光谱仪实验,将仪器设计和研发实践融入到理论学习当中,有助于提高学生的创新精神和实践能力,探索工程实践与课堂教学的有机融合模式。

雾滴谱仪的标准粒子计数校准测量与反演

为了提高国产雾滴谱仪的雾滴粒子粒径测量准确性,采用标准粒子进行雾滴谱的散射响应测试,并用最小均方算法对实际测量的雾滴谱的散射响应信号进行了反演,通过理论分析与实验验证,取得了最小均方算法在不同标准粒子响应信号下的粒径反演数据。结果表明,最小均方算法对标准粒子分布的反演能够减小粒径的分布误差,使不同尺寸的粒子得到准确区分,尺寸区分精度可以达到1μm。该研究为雾滴谱仪的精度提升提供了参考。

光波导输入的双通道同步定标虚拟成像相位阵列光谱仪

激光频率梳定标的虚拟成像相位阵列光谱仪有潜力同时实现超高光谱分辨率与波长定标精度,对于天文光谱探测有重要意义。然而,现有的研究工作中,虚拟成像相位阵列光谱仪采用常规的双通道光纤输入模式,在受环境干扰时,两个通道的同步性较差,相对漂移严重,从而降低了光谱仪的重复性定标精度。为解决该问题,提出一种以光波导作为输入器件的双通道虚拟成像相位阵列光谱仪,利用波导通道之间相对稳定的特性,实现更高水平的同步定标精度。通过对不同环境下光谱仪的稳定性进行研究得出,在相似的测试条件下,波导输入的虚拟成像相位阵列光谱仪的重复性定标精度明显优于光纤输入时的定标表现。

黄渤海沉积物有机碳光谱分析在不同仪器间的差异

光谱仪作为可见-近红外光谱分析核心工具,对于光谱分析的影响还有待深入研究。这里,以黄渤海沉积物为研究对象,利用安捷伦Cary 5000、 ASD FieldSpec 4、海洋光学QEPro三种光谱仪,研究有机碳含量的反射光谱及其光谱分析在不同光谱仪间的差异。其中,Cary 5000为室内台式光谱仪,FieldSpec 4和QEPro是便携式光谱仪;QEPro只能采集200~1 000 nm的反射率,而且反射率在三种光谱仪中最高;Cary 5000和FieldSpec 4能够采集完整的可见-近红外反射率(350~2 500 nm),光谱曲线几乎完全一致,尤其是近红外部分,但Cary 5000采集的反射率高于FieldSpec 4。三种光谱仪的光谱分析能力也存在显著差异,其中,Cary 5000的光谱分析能力最强,其光谱模型具有很强的预测能力,建模集r^(2)高达0.99,验证集r^(2)高达0.86,均方根误差(RMSE)在建模集和验证集分别为0.04、 0.11,相对分析偏差(RPD)高达2.6,显示了对黄渤海沉积物有机碳强大的预测能力。FieldSpec 4的建模集r^(2)很高,达到0.98,但验证集r^(2)仅为0.56, RMSE从建模集的0.06降为预测集的0.19, RPD仅为1.4,显示在黄渤海沉积物有机碳的预测中准确度很低。QEPro的建模集和验证集r^(2)都很低,分别为0.75、 0.59, RMSE保持稳定,均为0.18, RPD刚超出1.5(RPD=1.6),显示在黄渤海沉积物有机碳的预测上具有一定的准确度。可见,室内光谱仪比便携式光谱仪具有更强的光谱分析能力,可能是因为室内光谱仪的配置更好。同为便携式光谱仪,在黄渤海沉积物有机碳的光谱分析方面,QEPro具有和FieldSpec 4一样的光谱分析能力,甚至在稳定性上更好。由于QEPro的价格相对低廉,因此在室外沉积物/土壤碳氮光谱分析中,具有更好的性价比。该研究深入比较了不同光谱仪在相同样品的光谱分析中的差异,为不同研究的光谱分析及其模型转移提供了有效参考。

三种测量三棱镜折射率方法的讨论

折射率不仅与几何光学有关,与波动光学也有密切联系,对其的测量方法也多种多样。为了研究不同方法对测量折射率精度的影响,本文利用分光计实验仪器研究了三种不同实验方法测量了三棱镜的折射率,包括掠射法、最小偏向角法和布儒斯特角法,并对三种实验方法测量计算出来的折射率,进行了分析比较。实验结果表明,相对于布儒斯特角法测量三棱镜的折射率,掠射法和最小偏向角法测量的结果更为准确。本文为精确测量三棱镜折射率提供了可参考性的实验方法。