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.

LO-RAY-LIGH@ Diffraction Gratings in UV-VIS Spectroscopy

It has been more than half a century since the release of the first Shimadzu UV-VIS （UV-visible） spectrophotometer QB-50 in 1952, and during this time more than 160,000 UV-VIS spectrometers have been produced and installed in a wide variety of different applications. A lot of technical innovations have been implemented to improve the performance and significantly reduce the stray light levels. The latest innovation during development of sophisticated spectrophotometers is based on a new holographic exposure method and optimized etching process which has made it possible to produce both high-efficient and exceptionally low stray light gratings. These LO-RAY-LIGH~ gratings have guaranteed values of stray light at the intermediate position between zero-order and first-order lights. The values are measured by Shimadzu＇s laser stray-light-measuring system. The latest development in the series of UV-VIS spectrophotometers is the UV-2700 which is a true double beam double monochromator system in a compact design for high-precision spectral analysis of a wide range of samples including organic and inorganic compounds, biological samples, optical materials and photovoltaics. The high performance optical system is designed with ＂LO-RAY-LIGH＂ diffraction gratings, featuring highest efficiency and exceptionally low stray light. The spectrophotometer operates in the wavelength range from 185 nm to 900 nm and allows highly sophisticated applications such as direct measurement of high density samples up to 8 absorbance units without dilution.

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.