基于DMD的哈达玛变换近红外光谱仪的研究

发布时间：2019-05-17 05:39

【摘要】：随着化学计量学和计算机技术的快速发展,近红外光谱仪突破了其在传统农业中的应用局限,广泛应用于临床医学、石油化工、矿物质以及国防等领域,成为很多领域质量控制和品质分析的重要工具。哈达玛变换光谱仪以其测量速度快、信噪比高、分辨率高等优势成为微型光谱仪的研究热点。而随着研究和应用领域需求的不断提高,目前哈达玛变换近红外光谱仪亟待解决的问题是:如何在保持系统高分辨率的同时提高光谱仪的能量利用率并扩宽其工作光谱范围。本论文致力于这一问题,旨在通过改进光谱仪结构,实现哈达玛变换近红外光谱仪的高分辨率、高能量利用率和宽工作谱段,以满足更多研发和应用领域的需求。具体内容如下:针对目前哈达玛变换光谱仪分辨率较低的现状,分别研究了入射狭缝、准直透镜和成像透镜对系统分辨率的影响,研究了光栅衍射效率随入射波长与入射角度的变化情况,综合考虑系统体积与系统分辨率,选择最佳参数进行系统优化设计,对光栅多级次衍射进行分析,设计并搭建原理样机进行实验验证,实验测得的系统分辨率与模拟结果一致。该设计使光谱仪体积更小,分辨率更高。为提高入射光通量,提出两种改进的光谱仪光学系统结构。第一种为在入射狭缝前添加集光结构,集光结构借助柱面镜将圆形光束整形为与入射狭缝平行的带状光束。实验表明,相同条件下,该装置可以使通过入射狭缝的能量提高14.2%。为减少狭缝导致的大量光能量的遮拦,第二种改进型的光谱仪用光纤代替入射狭缝,用柱面镜作为成像透镜,对光栅色散后的圆形光束进行整形,使光纤在DMD上的像呈带状分布,提高了光谱仪的能量利用率和分辨率;采用M型对称光路设计,使最终聚焦到单点探测器上的光斑直径仅180?m,减小探测器体积,节约成本。为了在保持系统高分辨率的同时扩宽光谱仪的工作光谱范围,提出两种结构不同的光谱折叠哈达玛变换光谱仪。第一种光谱仪利用两个有一定夹角的子光栅将光源发出的波长为800~2000nm的光谱二维折叠分布在DMD表面。对光栅衍射效率随波长和入射角关系进行模拟,以确定两个子光栅的最佳入射角,模拟表明使用两个子光栅可以提高光栅在整个波段的平均衍射效率。系统整体优化设计后,光谱仪在全波段的分辨率为5.5nm。为减少系统杂散光,对两个子光栅的多级次衍射、DMD的二维衍射进行分析。第二种光谱仪通过自由曲面透镜将光源发出的宽波段光准直为两束波长不同、方向不同的平行光束,用一个平面光栅进行色散,实现了波长800~2400nm的光谱折叠。通过裁剪法建立自由曲面数学模型,利用Rounge-Kutta法求得自由曲面离散值,进而构建自由曲面透镜。该光谱仪在全波段的模拟分辨率约为10nm。对两种结构的光谱仪进行比较可以发现,当光谱折叠次数增多时,自由曲面准直的光谱折叠光谱仪在体积和能量利用率方面更占优势。设计结果表明,通过DMD上的光谱折叠,可以很好的解决由于DMD的尺寸限制导致的光谱分辨率与工作光谱范围的矛盾。
[Abstract]:With the rapid development of the chemometrics and the computer technology, the near-infrared spectrometer breaks through the limitation of its application in the traditional agriculture, and is widely used in the fields of clinical medicine, petrochemical industry, minerals and national defense, and has become an important tool for quality control and quality analysis in many fields. The Hadamard transform spectrometer has the advantages of fast measuring speed, high signal-to-noise ratio, high resolution and so on. With the increasing demand of research and application, the problem to be solved in the present Hadamard transform near-infrared spectrometer is how to improve the energy utilization of the spectrometer while keeping the system's high resolution and broaden its working spectral range. The aim of this paper is to improve the structure of the spectrometer, to realize the high resolution, high energy utilization rate and wide working spectrum of the Hadamard transform near-infrared spectrometer, so as to meet the needs of more research and development and application fields. The effect of the incident slit, the collimating lens and the imaging lens on the resolution of the system is studied. The change of the diffraction efficiency of the grating with the incident angle and the incident angle is studied. The system volume and the system resolution are considered, the optimal parameters are selected for system optimization design, and the multi-stage diffraction of the grating is analyzed, the principle prototype is designed and built, and the experimental verification is carried out, and the system resolution measured by the experiment is consistent with the simulation result. The design makes the volume of the spectrometer smaller and the resolution is higher. In ord to improve that flux of the incident light, two improved optical system structure of the spectrometer are proposed. The first is to add a light-collecting structure before the entrance slit, and the light-collecting structure shapes the circular light beam into a strip-shaped light beam parallel to the incident slit by means of a cylindrical mirror. The experiment shows that the energy of the incident slit can be increased by 14.2% under the same conditions. in order to reduce the shielding of a large amount of light energy caused by the slit, the second improved spectrometer replaces the incident slit with an optical fiber, uses a cylindrical mirror as an imaging lens, and shapes the circular light beam after the grating dispersion, so that the image of the optical fiber on the DMD is in a band-shaped distribution, The energy utilization rate and the resolution of the spectrometer are improved; the M-shaped symmetrical optical path is adopted to design the spot diameter of the final focusing to the single-point detector only by 180-m, so that the volume of the detector is reduced, and the cost is saved. In order to broaden the operating spectrum of the spectrometer while maintaining the high resolution of the system, two different spectral folding Hadamard transform spectrometers are proposed. The first spectrometer uses two sub-gratings with a certain included angle to distribute the two-dimensional folding of the light source with a wavelength of 800-2000 nm to the surface of the DMD. The diffraction efficiency of the grating is simulated with the relation of the wavelength and the incident angle to determine the optimal incident angle of the two sub-gratings, and the simulation shows that the average diffraction efficiency of the grating in the whole band can be improved by using the two sub-gratings. After the overall optimization of the system, the resolution of the spectrometer in the full-band is 5.5 nm. In order to reduce the stray light of the system, the two-dimensional diffraction of the two sub-gratings and the two-dimensional diffraction of the DMD are analyzed. The second spectrometer is used for collimating the wide-band light emitted by the light source into two parallel beams with different wavelengths and different directions by the free-surface lens, and the dispersion is carried out by a plane grating, so that the spectrum folding with the wavelength of 800-2400 nm is realized. The free-surface mathematical model is established by the cutting method, and the free-surface discrete value is obtained by the method of the Rounge-Kutta method, and the free-surface lens is further constructed. The spectrometer has a simulated resolution of about 10 nm in a full band. It can be found that the spectral folding spectrometer with free-surface collimation is more dominant in terms of volume and energy utilization when the number of times of the spectral folding is increased. The results show that the spectral resolution due to the size limitation of the DMD can be well solved by the spectral folding on the DMD.
【学位授予单位】：中国科学院研究生院(长春光学精密机械与物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH744.1

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