DOCSLIB.ORG

The COSMO Coronagraph Optical Design and Stray Light Analysis Dennis Gallagher*A, Zhen Wub, Brandon Larsona, Peter G

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The COSMO Coronagraph Optical Design and Stray Light Analysis Dennis Gallagher*A, Zhen Wub, Brandon Larsona, Peter G The COSMO coronagraph optical design and stray light analysis Dennis Gallagher*a, Zhen Wub, Brandon Larsona, Peter G. Nelsonc, Phil Oakleya, Scott Sewella Steven Tomczyka aThe National Center for Atmospheric Research High Altitude Observatory-Boulder, Colorado, bNanjing Institute of Astronomical Optics and Technology- Nanjing, China, cSierra Scientific Solutions- Boulder, Colorado ABSTRACT The Coronal Solar Magnetism Observatory Large Coronagraph (COSMO-LC) is a 1.5 meter Lyot coronagraph dedicated to measuring magnetic fields and plasma properties in the solar corona. The COSMO-LC will be able to observe coronal emissions lines from 530-1100 nm using a filtergraph instrument. COSMO-LC will have a 1 degree field of view to ob- serve the full solar corona out to 1 solar radius beyond the limb of the sun. This presented challenges due to the large Etendue of the system. The COSMO-LC spatial resolution is 2 arc-seconds per pixel (4k X 4k). The most critical part of the coronagraph is the objective lens that is exposed to direct sunlight that is five orders of magnitude brighter than the corona. Therefore, it is key to the operation of a coronagraph that the objective lens (O1) scatter as little light as possible, on order a few parts per million. The selection of the material and the polish applied to the O1 are critical in reducing scattered light. In this paper we discuss the design of the COSMO-LC and the detailed design of the O1 and other key parts of the COSMO-LC that keep stray light to a minimum. The result is an instrument with stray light below 5 mil- lionths the brightness of the sun 50 arc-seconds from the sun. The COSMO-LC has just had a Preliminary Design Re- view (PDR) and the PDR design is presented. Keywords: sun, coronagraph, corona, scatter, dust, lens 1. INTRODUCTION The Coronal Solar Magnetism Observatory Large Coronagraph (COSMO-LC) is a 1.5 meter aperture coronagraph that will observe the solar corona from 1.05 out to 2.0 solar radii. The wavelength span for COSMO-LC is (530-1100 nm) which includes key coronal emission lines such as Fe XIV 530.3nm, Fe X 637.4nm and near IR lines such as Fe XIII 1074.7nm, and the He I 1083.0nm chromospheric line. The High Altitude Observatory (HAO), a division of the National Center for Atmospheric Research in Boulder, CO currently operates two 20cm coronagraphs, the white light COSMO-K Coronagraph [1] and the Coronal Multi-channel Polarimeter (CoMP) instrument [2] on Mauna Loa on the big island of Hawaii. These coronagraphs observe the solar corona from 1.05 solar radii out to 3.0 solar radii. A very preliminary de- sign of the COSMO-LC was presented in 2012 [3]. HAO has performed several design trades and studies on various aspects of the COSMO-LC. The work presented in this paper is an extension of one of these studies that explores COS- MO-LC and stray light [4-5]. A key design requirement for a coronagraph is to reduce stray light in the instrument. The sky brightness next to the sun, ~1 arc-minute from the solar limb, on a clear day at locations such as Mauna Loa, located at an altitude of 11300ft, can be as low as a few millionths the brightness of the solar disk. Coronal emission lines are highly variable in brightness, but are typically in the range of 5-100 millionths of the brightness of the solar disk at ~ 1 arcminute from the solar limb. Therefore it is important that the design of a coronagraph have instrumental scatter as low as a few parts per million if observations of the corona are to be made with good signal to noise. Practically all the in- strumental stray light in a coronagraph is due to scattered and diffracted light from the O1 objective lens. The bulk of the scattered light is due to small polishing defects, mirco-roughness, and dust on the surface of the objective that are ex- posed to the direct sunlight. Diffracted light is controlled though the design of the Lyot coronagraph. In a coronagraph, an occulter blocks the intense light from the image of the solar disk. After the occulter, all the optics in a coronagraph are shadowed from the bright sun and can have simple commercial grade polished surfaces to meet stray light requirements. A key decision in the design of the COSMO-LC was the selection of a reflective vs. a refractive O1 objective for the coronagraph optical system. A design trade is presented here where the result was the selection of a refractive optical system for the COSMO-LC due to the stray light advantages of a lens vs. a mirror system. Ground-based and Airborne Telescopes VI, edited by Helen J. Hall, Roberto Gilmozzi, Heather K. Marshall, Proc. of SPIE Vol. 9906, 990654 · © 2016 SPIE · CCC code: 0277-786X/16/$18 · doi: 10.1117/12.2235234 Proc. of SPIE Vol. 9906 990654-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/10/2016 Terms of Use: http://spiedigitallibrary.org/ss/termsofuse.aspx In this paper we will discuss scattered light from the optical surfaces of a reflecting and refracting optical system along with scattered light from dust on the optical surfaces. The performance of the COSMO-LC in terms of image brightness due to scattered light from the O1 over the field of view is presented. The design of the main O1 objective lens is pre- sented along with polishing and cleanliness requirements. An overview of the current PDR design of the COSMO-LC is also presented. 2. LENS VS. MIRROR The trade between using a lens or a mirror is a very important one for an instrument with the stray light requirements of the COSMO-LC. Micro-roughness due to residual polishing defects (surface finish) and dust scatter light differently for a mirror and a lens. In this section we describe scattered light from surface finish on a mirror and a lens. We also de- scribe the effects of dust on a mirror and a lens and how dust increases scatted light. For the 1.5 meter COSMO-LC the cost of the lens would be significantly more than for a mirror, both in raw material and fabrication cost, another reason to carefully explore the lens vs. mirror selection of the objective lens for the COSMO-LC. 2.1 Scattering from surface finish The discussion of scattered light from optical surfaces has been well described in the literature. Works by [6] describe a method of relating the surface Power Spectral Density (PSD) to the Bidirectional Scattering Distribution Function (BSDF) with units of 1/sr. This relation is given by Equation 1. The integration of the BSDF is the Total Integrated Scat- ter TIS. Equation 1 BSDF(ß-ß0) = n S ( ) � ∆ � � TIS = (ß-ß0) ß The illumination wavelength is λ, is the incident angle,∫ is the scattering angle, ß-ß0 is the difference between the specular and the scattering angles, and S ( ) is the two dimensional (2-D) PSD of the optical surface. ∆n is the differ- ence between the index of refraction between the two media. For a mirror ∆n=2 and for a typical lens ∆n≈0.5. For the 2 COSMO-LC the incidence and scattering angles are small, so the cosine terms and, are set to ~1 in Equation 1. The ß-ß0 relation is used because scatter is somewhat invariant to incidence angle. Scatter is determined from the specular angle ß0. In our case ß0 0. The relation between BSDF and S ( ) in Equation 1 is valid for surfaces where the RMS roughness is much less than λ. To apply the units used in this paper Equation 1 can be rearranged to give Equation 2 2 where the PSD S ( ) is≅ in units of (Angstroms^2 mm^2) and is in units of Angstroms. 2 BSDF × n Equation 2 S ( )~ Å mm �× � � ∆ = sqrt( S ( ) ) � � The PSD, or S ( ) , is a quantity that can be measured directly∫ using a 2D interferometer. σ is the RMS surface rough- ness. The scale of features on the optical surface scatter light into angles that can be determined by the simple grating 2 equation. The BSDF is a description of how a surface will scatter light through angle. The BSDF of a surface can be found directly by measuring how light is scattered off a surface through angle in an instrument called a scatterometer. These data can then be used to derive the 2-D Power Spectral Density (PSD) for the surface using equation 1. The term 4 n 16 in Equation 1 becomes for a lens surface n=1.5, and for a mirror surface. One can 2 2 2 2 see that for a given surface PSD a mirror will display ~8-10 (n 1.45-1.5) times more scattering than a lens due to sur- ∆ � 4 � 4 � 4 face� finish. This� takes into account that� a lens �has two surfaces where a mirror� has a single � surface. The PSD is a physi- cal description of the optical surface and is wavelength independent.≅ The BSDF, or scattered light, has a 1 dependence. 2 � � � Proc. of SPIE Vol. 9906 990654-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/10/2016 Terms of Use: http://spiedigitallibrary.org/ss/termsofuse.aspx 2.2 Scattering from dust To further explore the comparison between a lens and a mirror we look at how dust adds to scatter light in a lens and mirror optical system. In practice no optical system is free of dust and this is especially true for an instrument located at a remote mountain top.
Load more

Recommended publications
  • Stray Light Correction on Array Spectroradiometers for Optical Radiation Risk Assessment in the Workplace a Barlier-Salsi
    Stray light correction on array spectroradiometers for optical radiation risk assessment in the workplace A Barlier-Salsi To cite this version: A Barlier-Salsi. Stray light correction on array spectroradiometers for optical radiation risk assessment in the workplace. Journal of the Society for Radiological Protection, Institute of Physics (IOP), 2014, J. Radiol.Prot., 34 (4), pp.doi:10.1088/0952-4746/34/4/915. 10.1088/0952-4746/34/4/915. hal- 01148941 HAL Id: hal-01148941 https://hal.archives-ouvertes.fr/hal-01148941 Submitted on 5 May 2015 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Stray light correction on array spectroradiometers for optical radiation risk assessment in the workplace A Barlier-Salsi Institut national de recherche et de sécurité (INRS) E-mail: [email protected] Abstract. The European directive 2006/25/EC requires the employer to assess and if necessary measure the levels of exposure to optical radiation in the workplace. Array spectroradiometers can measure optical radiation from various types of sources; however poor stray light rejection affects their accuracy. A stray light correction matrix, using a tunable laser, was developed at the National Institute of Standards and Technology (NIST).
    [Show full text]
  • Landsat 9 Thermal Infrared Sensor 2 Preliminary Stray Light Assessment
    TIRS-2 Instrument Project Thermal Infrared Sensor-2 Landsat 9 Thermal Infrared Sensor 2 Preliminary Stray Light Assessment Joel McCorkel (NASA Goddard) Matt Montanaro (NASA Goddard) June Tveekrem (NASA Goddard) John Stauder (Space Dynamics Lab) Allen Lunsford (NASA Goddard) Eric Mentzell (NASA Goddard) Jason Hair (NASA Goddard) Dennis Reuter (NASA Goddard) 1 Stray Light Assessment Objective for TIRS-2 • Landsat 8 / Thermal Infrared Sensor – 1 (TIRS-1) has significant stray light in its optical system. • Landsat 9 / TIRS-2 is a near-replica of TIRS-1. • Stray light effects on TIRS-1 imagery have now been corrected in the ground processing system. • To prevent the problem with TIRS-2, the instrument has built-in mitigations to drastically reduce stray light. • Major effort to model and test the design changes in TIRS-2. • Results of the initial scattering measurements in thermo-vacuum conditions along with results of the optical scattering model are presented here. 2 Stray Light Problem on Landsat 8 / TIRS-1 • Landsat 8 / TIRS-1 instrument found to have a stray light issue where off-axis radiance scatters onto the focal plane. • Demonstrated through on-orbit out-of-field scans of the Moon. Moon position 15-deg Field-of-View & approx. size Detector A Detector B k-- bandlO ~ bandll Detector C Scattered Signal 3 Lunar Scans for TIRS-1 • Flagged lunar locations where scatter was recorded by the detectors. • Discovered that there 40 is a strong scattering 30 source in the optical system approximately 20 13-deg off-axis. 10 , 0)Q) I 0. • Very weak 22-deg "a;" o· Ol C: scatter also observed <:I'.: (not indicated here) Strong -30 13-deg scatter -40 Band 10 Band 11 -50 ~-~-~-~-~ -50 ~-~-~-~-~ -20 -10 0 10 20 -20 -10 0 10 20 Angle [D eg] Ang le [Deg] 4 Cause of Scattering for TIRS-1 • Detailed optical models pin-pointed scattering surface in the telescope.
    [Show full text]
  • The Space Infrared Interferometric Telescope (SPIRIT): High- Resolution Imaging and Spectroscopy in the Far-Infrared
    Leisawitz, D. et al., J. Adv. Space Res., in press (2007), doi:10.1016/j.asr.2007.05.081 The Space Infrared Interferometric Telescope (SPIRIT): High- resolution imaging and spectroscopy in the far-infrared David Leisawitza, Charles Bakera, Amy Bargerb, Dominic Benforda, Andrew Blainc, Rob Boylea, Richard Brodericka, Jason Budinoffa, John Carpenterc, Richard Caverlya, Phil Chena, Steve Cooleya, Christine Cottinghamd, Julie Crookea, Dave DiPietroa, Mike DiPirroa, Michael Femianoa, Art Ferrera, Jacqueline Fischere, Jonathan P. Gardnera, Lou Hallocka, Kenny Harrisa, Kate Hartmana, Martin Harwitf, Lynne Hillenbrandc, Tupper Hydea, Drew Jonesa, Jim Kellogga, Alan Koguta, Marc Kuchnera, Bill Lawsona, Javier Lechaa, Maria Lechaa, Amy Mainzerg, Jim Manniona, Anthony Martinoa, Paul Masona, John Mathera, Gibran McDonalda, Rick Millsa, Lee Mundyh, Stan Ollendorfa, Joe Pellicciottia, Dave Quinna, Kirk Rheea, Stephen Rineharta, Tim Sauerwinea, Robert Silverberga, Terry Smitha, Gordon Staceyf, H. Philip Stahli, Johannes Staguhn j, Steve Tompkinsa, June Tveekrema, Sheila Walla, and Mark Wilsona a NASA’s Goddard Space Flight Center, Greenbelt, MD b Department of Astronomy, University of Wisconsin, Madison, Wisconsin, USA c California Institute of Technology, Pasadena, CA, USA d Lockheed Martin Technical Operations, Bethesda, Maryland, USA e Naval Research Laboratory, Washington, DC, USA f Department of Astronomy, Cornell University, Ithaca, USA g Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA h Astronomy Department, University of Maryland, College Park, Maryland, USA i NASA’s Marshall Space Flight Center, Huntsville, Alabama, USA j SSAI, Lanham, Maryland, USA ABSTRACT We report results of a recently-completed pre-Formulation Phase study of SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 µm.
    [Show full text]
  • Stray Light Measurement on Lenscheck™ Lens Measurement Systems
    Stray Light Measurement on LensCheck™ Lens Measurement Systems Optikos is seeing continued interest in measuring stray light from our customers’ products and anticipates substantial growth in suppliers and end-users specifying and testing stray light performance. This is encouraging as it shows an increasing appreciation for the significance of stray light in optical imaging systems. The LensCheck instrument is an ideal and affordable instrument for enabling measurement of both Veiling Glare Index and Glare Spread Function. Optikos LensCheck™ systems are designed to meet the increasing demand to measure the effects of stray light on optical imaging systems. Although unwanted light in a camera may pose a minor issue for the casual photographer, the resulting degradation in system performance in many industrial and automotive applications can represent significant financial costs, cause serious safety issues, or make or break a successful product launch. Manufacturers are asking vision systems to take on more and more challenging imaging tasks across non-ideal imaging environments. Many applications require imaging scenes with extraordinarily high dynamic range content. For example, automotive cameras must be able to identify a pedestrian or traffic light at night while also imaging an on-coming car’s headlights. This performance must be determined while viewing through protective windows that may be scratched or covered with debris. Windows, debris, optical elements, and even the sensor can result in unintended radiation striking the detector. This light can potentially overwhelm the desired signal and introduce computational errors. Above is an example of a ghost reflection that would be characterized in a GSF measurement. The designers, manufacturers and consumers of these lens and camera systems require a quantitative measurement of stray light.
    [Show full text]
  • Non-Destructive Characterization of Anti-Reflective Coatings on PV Modules
    1 Non-destructive Characterization of Anti-Reflective Coatings on PV Modules Todd Karin ∗, David Miller y, Anubhav Jain ∗ ∗Lawrence Berkeley National Laboratory, Berkeley, CA, U.S.A yNational Renewable Energy Laboratory, Golden, CO, U.S.A Abstract—Anti-reflective coatings (ARCs) are used on the vast example, multi-layer coatings composed of hard materials with majority of solar photovoltaic (PV) modules to increase power a high mechanical modulus have been found to be significantly production. However, ARC longevity can vary from less than 1 more durable to abrasion [7]. Because there are no pores, the year to over 15 years depending on coating quality and deploy- ment conditions. A technique that can quantify ARC degradation permeability of water is reduced, preventing moisture ingress non-destructively on commercial modules would be useful both and subsequent damage in the event of glass corrosion [8] of for in-field diagnostics and accelerated aging tests. In this paper, the underlying substrate and/or additional strain in the event we demonstrate that accurate measurements of ARC spectral of freezing. reflectance can be performed using a modified commercially- Although the single-layer ARCs on the market today can available integrating-sphere probe. The measurement is fast, accurate, non-destructive and can be performed outdoors in have an expected lifetime of 15 years [1], ARC lifetime full-sun conditions. We develop an interferometric model that depends on the coating deposition process [9] and deploy- estimates coating porosity, thickness and fractional area coverage ment conditions including heat, humidity, soiling and fre- from the measured reflectance spectrum for a uniform single- quency/method of cleaning.
    [Show full text]
  • Stray Light Measurement
    Stray Light Measurement on LensCheck™ Systems Haskell Kent, Roy Youman July 1, 2020 Copyright ©2020 Optikos Corporation Contents Section 1. Background .......................................................................................................................................... iv Section 2. What is Stray Light? .............................................................................................................................. v Section 3. How OpTest® Software Measures Stray Light .................................................................................... vi 3.1 Veiling Glare Index .................................................................................................................................... vi 3.2 How does the VGI measurement work with LensCheck and OpTest® 7?............................................... vii 3.3 What lenses can I test with the Stray Light Kit? ........................................................................................ ix 3.4 What are the limitations of the Stray Light Kit? ......................................................................................... ix 3.5 Glare Spread Function (GSF) .................................................................................................................... ix 3.6 How does the LensCheck’s new GSF measurement work with OpTest 7? ............................................... x 3.7 On what lenses can I measure GSF? ........................................................................................................
    [Show full text]
  • Telescope Stray Light Telescope Stray Light
    TELESCOPE STRAY LIGHT – FUNDAMENTAL OPTICAL PLUMBING & EARLY EXPERIENCE WITH SOFIA SOFIA SCIENCE CENTER PATRICK WADDELL 15FEB2017 1 STRAY LIGHT ENGINEERING: SUCCESSFUL SYSTEMS (STRUCTURES & COATINGS) FOR MILLENNIA 2 STRAY LIGHT ENGINEERING: NON-TRANSMISSIVE SOLUTIONS THROUGH MID- 20TH CENTURY 3 STRAY LIGHT FOR OPTICAL ASTRONOMY , DETECTING AND ANALYZING SCIENCE TARGETS AND TARGET FEATURES REQUIRES DIRECT SOURCE MEASUREMENT, USU ALLY T O SO ME QU ALITY, SUC H AS AT OR ABOVE A SPECIFIC S/N. DEF. STRAY LIGHT IS LIGHT CAPTURED & MEASURED WITHIN A SYSTEM THAT IS NOT FROM THE INTENDED SOURCE(S) BASED ON THE SENSOR DESIGN. THIS UNINTENDED SIGNAL CONTRIBUTES AMPLITUDE ERRORS, A MPLITUUUCUOOS(OSSO/SODE RELATED FLUCT U ATIO N NO I S E ( P O I SSON /SH O T NOISE), AND COMPLEX CALIBRATION PROBLEMS, SUCH AS CAUSTICS, AND VARIABLE CONTRIBUTIONS. 4 STRAY LIGHT STRAY LIGHT SOURCE EXAMPLES: . BRIGHT OBJECTS NEAR THE LINE OF SIGHT, MOON, PLANETS, ETC . SKY GLOW . THERMAL RADIATION ( IR A PPLICATIONS) . MICRO-ROUGH AND/OR CONTAMINATED OPTICAL SURFACES; “TURNED” EDGES . REFLECTIONS FROM BAFFLES & STRUCTURES . TRANSMISSIVE OPTICS INTERNAL REFLECTIONS; GRATING ORDER SEPARATION . DESIGN FLAWS THAT PERMIT LIGHT TO ENTER AND HIT DETECTORS DIRECTLY 5 STRAY LIGHT TO ACHIEVE THE DESIRED SCIENCE A NUMBER OF MEANS ARE EMPLOYED TO CONTROL BACKGROUND SIGNAL CONTRIBUTION: . BLOCKING: DESIGN & INCLUDE EFFECTIVE BAFFLES & STRUCTURES; DEFLECTION WITH SPECIAL OPTICS . ATTENUATING/SCATTERING: PROVIDE SURFACES WITH ABSORBING COATINGS, ALSO DIFFUSE/LAMBERTIAN – NON-SPECULAR PROPERTIES . REAL TIME MODULATION: CHOPPING & NODDING . MODEL BEFORE COMMITTING TO BUILD TO REDUCE PERFORMANCE RISKS: ASAP, APART/PADE, ZEMAX 6 STRAY LIGHT – THE SDSS 2.5M INDUSTRIAL SCALE IMAGING AND SPECTROMETRY IMAGING WAS THE DRIVER, DEFINED SYSTEM CHALLENGES: .
    [Show full text]
  • Correction of Stray Light in Spectrographs: Implications for Remote Sensing
    Correction of stray light in spectrographs: implications for remote sensing Yuqin Zong, Steven W. Brown, B. Carol Johnson, Keith R. Lykke, and Yoshi Ohno National Institute of Standards and Technology, Gaithersburg, MD 20899 ABSTRACT Spectrographs are used in a variety of applications in the field of remote sensing for radiometric measurements due to the benefits of measurement speed, sensitivity, and portability. However, spectrographs are single grating instruments that are susceptible to systematic errors arising from stray radiation within the instrument. In the application of measurements of ocean color, stray light of the spectrographs has led to significant measurement errors. In this work, a simple method to correct stray-light errors in a spectrograph is described. By measuring a set of monochromatic laser sources that cover the instrument’s spectral range, the instrument’s stray-light property is characterized and a stray-light correction matrix is derived. The matrix is then used to correct the stray-light error in measured raw signals by a simple matrix multiplication, which is fast enough to be implemented in the spectrograph’s firmware or software to perform real-time corrections: an important feature for remote sensing applications. The results of corrections on real instruments demonstrated that the stray-light errors were reduced by one to two orders of magnitude, to a level of approximately 10-5 for a broadband source measurement, which is a level less than one count of a 15-bit resolution instrument. As a stray-light correction example, the errors in measurement of solar spectral irradiance using a high- quality spectrograph optimized for UV measurements are analyzed; the stray-light correction leads to reduction of errors from a 10 % level to a 1 % level in the UV region.
    [Show full text]
  • The Improvement on the Performance of DMD Hadamard Transform Near-Infrared Spectrometer by Double Filter Strategy and a New Hadamard Mask
    micromachines Article The Improvement on the Performance of DMD Hadamard Transform Near-Infrared Spectrometer by Double Filter Strategy and a New Hadamard Mask Zifeng Lu 1,2, Jinghang Zhang 1, Hua Liu 1,2,*, Jialin Xu 3 and Jinhuan Li 1,2 1 Center for Advanced Optoelectronic Functional Materials Research, and Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, 5268 Renmin Street, Changchun 130024, China; [email protected] (Z.L.); [email protected] (J.Z.); [email protected] (J.L.) 2 Demonstration Center for Experimental Physics Education, Northeast Normal University, 5268 Renmin Street, Changchun 130024, China 3 Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China; [email protected] * Correspondence: [email protected]; Tel.: +86-180-0443-0180 Received: 7 December 2018; Accepted: 15 February 2019; Published: 23 February 2019 Abstract: In the Hadamard transform (HT) near-infrared (NIR) spectrometer, there are defects that can create a nonuniform distribution of spectral energy, significantly influencing the absorbance of the whole spectrum, generating stray light, and making the signal-to-noise ratio (SNR) of the spectrum inconsistent. To address this issue and improve the performance of the digital micromirror device (DMD) Hadamard transform near-infrared spectrometer, a split waveband scan mode is proposed to mitigate the impact of the stray light, and a new Hadamard mask of variable-width stripes is put forward to improve the SNR of the spectrometer. The results of the simulations and experiments indicate that by the new scan mode and Hadamard mask, the influence of stray light is restrained and reduced.
    [Show full text]
  • The Stray Light Absorption and Anti-Photobleaching Capacity of Matting Materials on Optical System
    The Stray Light Absorption and Anti-photobleaching Capacity of Matting Materials on Optical System Rou-Jhen Chen, Chun-Han Cho, Chia-lien Ma, Liang-Chieh Chao, Kuo-Cheng Huang and Yu-Hsuan Lin Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu, Taiwan Keywords: Matting Materials, Stray Light, Anti-photo Bleaching. Abstract: Eliminating stray light is a very important item in optimizing optical systems. The typical method is to use matting materials to coat onto the optomechanical component. However, the material will deteriorate or bleaching after being exposed to long periods of time and high UV energy. The performance of the optical system will be therefore affected. In this study, the anti-photobleaching capacity of matting materials on various substrates was discussed. A high intensity UV source was used to radiate the samples for long time. The changes of the morphology and relative reflectance of sample were observed and analysed. Also, a 355 nm pulsed laser was used to perform the surface modification on samples. An improvement of the matting performance was expected. This study succeeded in establishing a comparing procedure, which enabled the characteristic comparison between the various experimental conditions. This study provides a useful database for the development of matting material technology. 1 INTRODUCTION be overcome by the anti-reflective film coated on the lens surfaces and the matting materials processed on Optical systems are widely used in various fields the optomechanical component (Patterson, 2003) such as imaging, illumination, and spectral (Benjamin, 1962). The anti-reflection coatings were detection. The modules of its extension are very a common and mature technology, we notice that the versatile and closely related to people's modern life.
    [Show full text]
  • The Large UV/Optical/Infrared Surveyor Decadal Mission Concept Thermal System Architecture Kan Yang1, Matthew R
    49th International Conference on Environmental Systems 7-11 July 2019, Boston, Massachusetts ICES-2019-312 The Large UV/Optical/Infrared Surveyor Decadal Mission Concept Thermal System Architecture Kan Yang1, Matthew R. Bolcar2, Jason E. Hylan3, Julie A. Crooke4, Bryan D. Matonak5, Andrew L. Jones6, Joseph A. Generie7 NASA Goddard Space Flight Center, Greenbelt MD 20771 and Sang C. Park8 Harvard Smithsonian Center for Astrophysics, Cambridge, MA 02138 The Large Ultraviolet/Optical/Infrared (LUVOIR) Surveyor is one of four large strategic mission concept studies commissioned by NASA for the 2020 Decadal Survey in Astronomy and Astrophysics. Slated for launch to the second Lagrange point (L2) in the mid-to-late 2030s, LUVOIR seeks to directly image habitable exoplanets around sun-like stars, characterize their atmospheric and surface composition, and search for biosignatures, as well as study a large array of astrophysics goals including galaxy formation and evolution. Two observatory architectures are currently being considered which bound the trade-off between cost, risk, and scientific return: a 15-meter diameter segmented aperture primary mirror in a three- mirror anastigmat configuration, and an 8-meter diameter unobscured segmented aperture design. To achieve its science objectives, both architectures require milli-Kelvin level thermal stability over the optics, structural components, and interfaces to attain picometer wavefront RMS stability. A 270 Kelvin operational temperature was chosen to balance the ability to perform science in the near-infrared band and the desire to maintain the structure at a temperature with favorable material properties and lower contamination accumulation. This paper will focus on the system-level thermal designs of both LUVOIR observatory architectures.
    [Show full text]
  • Stray Light Correction
    NEUBrew NOAA-EPA Brewer Network StrayLightCorrection.pdf File Name Stray Light Correction Introduction Scattering by the grating is the dominant source of stray light in grating spectrometers like the Brewer MKIV. However, holographic gratings have lower stay light for higher line density. Therefore gratings of the following three Brewer models have stray light in the following descending order: MKIV, MKII, MKIII. Other sources of stray light include: (2) scattering by mirror surfaces, (3) scattering by surfaces of lenses and filters, (4) scattering by striae and inclusions in optical materials of lenses and filters, (5) multiple reflections between surfaces of lenses and filters that create weak out of focus secondary images, (6) Rayleigh and Mie scattering by air and dust particles in the air within the spectrometer, (7) scattering by housing surfaces, (8) Rayleigh scattering by the volume of glass and fused silica, (9) distortions due to thermal gradients in the air within the spectrometer, and (10) diffraction on the apertures. There are also ghosts caused by grating defects. Both the grating ghosts and specular reflections (glints) from aperture edges and optical element mounts are strongly wavelength dependent. Due to instrument contamination with dust the stray light is expected to increase after field deployment. This may have a larger relative effect with the MKIII (in the second spectrometer of the double) with a grating that scatters less than in the MKIV with a lower groove density grating that scatters more. The stray light results in a finite out-of-band rejection (OBR), meaning that light of other more distant wavelengths than those specified by slit function’s fwhm also contributes to the signal.
    [Show full text]