End-to-end computational design for an EUV solar corona multispectral imager with stray light suppression

An extreme ultraviolet solar corona multispectral imager can allow direct observation of high temperature coronal plasma,which is related to solar flares,coronal mass ejections and other significant coronal activities.This manuscript proposes a novel end-to-end computational design method for an extreme ultraviolet(EUV)solar corona multispectral imager operating at wavelengths near 100 nm,including a stray light suppression design and computational image recovery.To suppress the strong stray light from the solar disk,an outer opto-mechanical structure is designed to protect the imaging component of the system.Considering the low reflectivity(less than 70%)and strong-scattering(roughness)of existing extreme ultraviolet optical elements,the imaging component comprises only a primary mirror and a curved grating.A Lyot aperture is used to further suppress any residual stray light.Finally,a deep learning computational imaging method is used to correct the individual multi-wavelength images from the original recorded multi-slit data.In results and data,this can achieve a far-field angular resolution below 7",and spectral resolution below 0.05 nm.The field of view is±3 R_(☉)along the multi-slit moving direction,where R☉represents the radius of the solar disk.The ratio of the corona's stray light intensity to the solar center's irradiation intensity is less than 10-6 at the circle of 1.3 R_(☉).

Compound diffractive telescope system:design,stray light analysis,and optical test

The compound diffractive telescope is a novel space optical system which combines the structure of compound eyes with diffractive optics and so it has a lighter weight, a wider field of view （FOV）, a lower cost as well as looser fabrication tolerance. In this paper, the design of a compound diffractive telescope composed of one primary lens and twenty-one eyepieces is introduced. Then the influence of diffraction orders on the performance of the system is analysed. A modified phase function model of diffractive optics is proposed to analyse the modulation transfer function （MTF） curves for 0° FOV, which provides a more accurate prediction of the performance of the system. In addition, an optimized mechanism is also proposed to suppress stray light. The star image and resolution tests show that the system can achieve diffraction limit imaging within ±2° of FOV and 4-4 mm of eccentricity. Finally, a series of pictures of an object are taken from different channels, and the splicing of pictures from adjacent FOVs is demonstrated. In summary, the designed system has been proved to have great potential applications.

Optical Design and Stray Light Analysis of the Space Infrared Optical System

This article describes a novel configuration design for a re-imaging off-axis catadioptric space infrared optical system,and in order to satisfy the signal noise ratio requirements of the system,the stray light of the system is necessary to analyze and restrain. The optical system with a focal length of 1 200 mm,an entrance pupil diameter of 600 mm,an F-number of 2,a field of view of 3°× 0. 15°,a working wave band of 8 μm-10 μm,and the image quality of the optical system almost approach to diffraction limits in all field of view.Then the mathematical models of stray light are built,and the suppressive structure is established to eliminate the effect of stray light. Finally,TraceP ro is used to analyze and simulate stray light with and without the suppressive structure,and also get the results of the PST curves. The results indicate that appropriate optical system and suppressive structure can highly reduce the stray light of the space infrared optical system.

Stray light suppression in BRDF measurement infrared optical system

A set of system based on personal computer for the bi-directional reflectance distribution function (BRDF) measurement was developed, whose laser wavelengths cover 0.6328, 1.34, 3.39, and 10.6 μm from visible to infrared. Stray light in BRDF measurement system was analyzed. It can be reduced and suppressed by the design of the system light path in BRDF measurement system, the choice of the measuring scheme, the processing to the optoelectronic signal, and the radiation control of the optical components and mechanical equipments. So the minimum measurable value of BRDF is less than 10-5/sr.

Near-infrared fundus camera based on polarization switch in stray light elimination

This letter shows that the human eye fundus tissue has higher reflectivity at the near-infrared （NIR） wavelength, and that some aberrations exist at the pre-optical system from cornea to vitreous. We design a NIR fundus camera with inner focusing, which can be applied to the -10 D to 10 D range of vision and has the advantage of ensuring the stability of image when is focused. Considered as Liou＇s eye aberration model, we correct the integrated aberration to ensure a 100 lp/mm resolution when we complete the assembly and calibration of the fundus camera. Kohler illumination is also applied to obtain uniform fundus illumination. Moreover, we put forward a novel method for stray light elimination based on polarization switch, which inhibits ghost image formation near the focal plane when the illumination beam is reflected by the eyepiece surface. The result shows that this method is effective in ensuring an illumination uniformity of 80%, with the advantage of simple structure and easy assembly.

Reducing the stray light of holographic gratings by shifting the substrate a short distance in the direction parallel or perpendicular to the exposure interference fringes

This research proposes a simple and practical method to make low-stray-light gratings, where the substrate shifts about a 1 mm distance in the direction parallel or perpendicular to the exposure interference fringes. When the substrate shifts, a reference grating next to the substrate is used to adjust in real time the phase of the exposure interference fringes relative to the substrate. Shifting eliminates the exposure defects and therefore decreases the stray light of gratings. Several gratings are successfully made by using this method, which have straighter grooves,smoother surfaces, and lower stray light than gratings made in conventional interference lithography.

衍射复眼望远镜系统光学特性分析

衍射复眼望远镜是将衍射物镜和按生物复眼结构排列的目镜组结合在一起的新型空间光学成像系统。文中首先介绍了该系统的结构特点,根据衍射物镜的衍射效率计算公式,在ASAP软件中对设计波长下的子目镜系统进行了分析,证明该系统视场角可扩展至±2°;对非设计波长λF下系统的成像信噪比进行详细分析,其中0通道子目镜中心和边缘视场信噪比分别为57.19dB、47.2dB,其它通道相应信噪比均有所下降。在物镜、目镜分离情况下,对非成像光源、由机械结构产生的二次杂光进行了分析。综合分析表明,系统在±2°范围内可成清晰图像,且图像中心信噪比高于边缘。最后,通过实验分别对中心和边缘子目镜系统成像,证实了上述分析结果的正确性。

激光喇曼分光计超低杂散光测试中有关问题的探讨

本文根据激光喇曼分光计中超低杂散光测试的若干特殊问题提出了几点考虑。为了获得10^(-12)量级以下的杂散光测试限,文章重点就本实验所用的测试光源,前置单色器,光入射方式、分段减光方法及光电检测系统等问题进行了一些讨论,并给出了相应的实验结果。

平面光栅杂散光测试仪模型设计及消杂光技术研究

杂散光是平面光栅的重要性能指标,光栅杂散光的测量一直是光栅研制领域的难题。为实现仪器自身杂光低于10^(-8)量级,以满足对平面光栅杂散光10^(-7)量级的精确测量要求,基于标量衍射理论和经典Fresnel-Kirchhoff衍射理论,对光谱仪器中的光栅杂散光进行了理论分析,设计了平行光照射条件下光栅杂散光测试仪的光机模型。利用杂散光分析软件ASAP建立紫外单色光入射下光栅杂散光测试仪的散射模型并对其进行仿真计算,分析仪器杂光的主要来源及散射路径,据此提出了用于降低仪器散射光和光栅多次衍射光的挡光环、叶片、光阑、光学陷阱等四种杂光抑制结构。最后,采用ASAP软件对增加抑制结构前后的仪器杂光相对强度进行了对照分析。仿真及分析结果表明,仪器杂光在测试波长±100 nm范围内的最大值由采用杂光抑制结构前的10^(-6)量级以上降低至10^(-9)量级以下,已满足光栅杂散光测试仪的设计需求,即可实现刻线密度为300~3 600 gr·mm^(-1)的光栅杂散光10^(-7)量级精确测量。该研究方法及结果将为平面光栅杂散光测试仪研制提供理论依据。

Comparison of ring 1 parameters in 37-segment multifocal electroretinography between onset and offset conditions of ring 2 to 4 in normal subjects

AIM: To investigate whether the response of a central hexagonal element corresponding to the macular area in conventional multifocal electroretinography(mfERG) tests was the same as that of experimental mfERG using single central hexagonal element stimulation. METHODS: Prospective, observational study. Thirty healthy subjects were included in this study. mfERG recordings were performed according to two protocols: stimulus with 37 hexagonal elements(protocol 1), and stimulus with a single central element created by deactivating the other 36 hexagonal elements(protocol 2). We compared differences between ring 1 parameters in each protocol. RESULTS: In protocol 1, the first positive component(P1) implicit time and P1 amplitude were 37.8±1.8 ms and 6.3±2.7 μV. After single element stimulation(protocol 2), double positive waves appeared. The implicit time and amplitude of P1 were 40.7±2.4 ms(P<0.001) and 9.1±3.3 μV(P=0.001), respectively. The implicit time and amplitude of the second positive component(P2) were 68.0±4.5 ms(P<0.001, compared with P1 in protocol 1) and 12.3±4.7 μV(P<0.001, compared with P1 in protocol 1), respectively. The amplitude of P2 in protocol 2 was about two times higher than that of P1 in protocol 1. CONCLUSION: mfERG responses of a central hexagonal element in a single element stimulation protocol are different from those of multiple element stimulation. The positive wave is more enhanced compared to that of the conventional protocol and it elongated into two wavelets.

Development of infrared spectral radiation measurement system of a non-luminous flame

The spectral radiation characteristic of a non-luminous flame is analyzed. The apparatus and the calibration procedure based on infrared emission spectrometry for measurements of the flame are introduced. The influence of background radiation and stray light on the measurement results could be reduced and suppressed by the design of thermolator and digital lock-in technique. A blackbody cavity was used as reference emission source to calibrate the system that completed absolute measurement. The spectral mea- surement range is 1-20μm. The least measuring distance and the lowest power detected at the entrance pupil are 550 mm and 10^-9 W/cm^2, respectively. The experimental results show that the measure error is less than 10%.

Study on validation method of visible imagery spatial resolution of imager on geostationary platform

Based on the analysis for the main elements of the total modulation transfer function （MTF） of imager on geostationary platform, the precise evaluation for its low spatial frequency spectrum has been achieved. Meanwhile, it is pointed out that the main cause of imagery spatial resolution lower than the designed value is the ＂slight defocus＂ of imager focal plane array （FPA）. The validation method for visible imagery spatial resolution is proposed based on the analysis of defocused optical system model and edge-spread-function （ESF）, the relative error is less than 7% after alleviating stray light effects. This method has been applied in the in-orbit ground testing of FY-2C geostationary meteorological satellite successfully.

Near-field holography enhanced with antireflection coatings--an improved method for fabricating diffraction gratings

Near-field holography（NFH）, with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduced by the integration of antireflective coatings（ARCs） simplifies the NFH process relative to that of setups using refractive index liquids. Based on the proposed NFH with ARCs, gold-coated laminar gratings were fabricated using NFH and subsequent ion beam etching. The efficiency angular spectrum shows that the stray light of the gratings is reduced one level of magnitude by the suppression of interface reflections during NFH.