Reflectivity, polarization properties, and durability of metallic mirror coatings for the European Solar Telescope

Feller, A.; Krishnappa, N.; Pleier, O.; Hirzberger, J.; Jobst, Paul Johannes; Schürmann, M.

doi:10.1117/12.927080

Cited by 8 publications

(5 citation statements)

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“…where R M (λ) is the mirror reflectivity as a function of wavelength in percent, and m and b are constants. The data for R M (λ) are taken from Feller et al (2012) who present measurements of five mirror samples coated according to the Gemini recipe, a lab reference, one prior to cleaning in 2009, and three post cleaning in 2009, 2010 and 2011 which we used to create a grid. We linearly interpolated in this grid of spectra based on two parameters, the age a and condition c (where c = 0 after cleaning and c = 1 before cleaning).…”

Section: Gemini North Observationsmentioning

confidence: 99%

HIPPI-2: A versatile high-precision polarimeter

Bailey

Cotton

Kedziora-Chudczer

et al. 2020

Publ. Astron. Soc. Aust.

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We describe the High-Precision Polarimetric Instrument-2 (HIPPI-2) a highly versatile stellar polarimeter developed at the University of New South Wales (UNSW). Two copies of HIPPI-2 have been built and used on the 60-cm telescope at Western Sydney University's (WSU) Penrith Observatory, the 8.1-m Gemini North Telescope at Mauna Kea and extensively on the 3.9-m Anglo-Australian Telescope (AAT). The precision of polarimetry, measured from repeat observations of bright stars in the SDSS g band, is better than 3.5 ppm (parts per million) on the 3.9-m AAT and better than 11 ppm on the 60-cm WSU telescope. The precision is better at redder wavelengths and poorer in the blue. On the Gemini North 8-m telescope the performance is limited by a very large and strongly wavelength dependent telescope polarization that reached 1000's of ppm at blue wavelengths and is much larger than we have seen on any other telescope.

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Section: Gemini North Observationsmentioning

confidence: 99%

HIPPI-2: A versatile high-precision polarimeter

Bailey

Cotton

Kedziora-Chudczer

et al. 2020

Publ. Astron. Soc. Aust.

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“…Dielectric layers consisting of SiO 2 , Al 2 O 3 , , Si 3 N 4 , , or SiN x , − have been used as overcoats for confinement of the silver layer and protection from environmental degradation by tarnishing. Most of the degradation studies performed on space silver-based mirrors addressed the efficiency of the protection layer and the effect of aging on the optical properties. ,,− Few studies were found to discuss their degradation mechanisms. − …”

Section: Introductionmentioning

confidence: 99%

Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis

et al. 2017

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In this work, we addressed the local degradation mechanisms limiting the prelaunch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on lightweight SiC substrates and protected by thin SiO overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous HS. The results show that tarnishing is locally initiated by the formation of AgS columns erupting above the stack surface. AgS growth is promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result of an imperfect protection by the SiO overcoat. Channels most likely connect the silver layer to its environment through the protection layer, which enables local HS entry and AgS growth. The silver sulfide columns grow in number and size eventually leading to coalescence with increasing HS exposure. In more advanced stages, tarnishing slows down owing to saturation of all pre-existing imperfectly protected sites of preferential sulfidation. However, it progresses radially at the basis of the AgS columns underneath the protection layer, consuming the metallic silver layer and deteriorating the protecting overcoat.

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“…Silver coatings may be a suitable substitution for the Al coating. Unfortunately, our environments have the molecules of O, O − , H 2 O 2 , SO 2 , and Cl − in the air resulting in AgCl, AgSO 4 , AgNO 3 , or Ag 2 S to degrade the film qualities [ 14 , 15 , 16 , 17 ]. Developing stacks of thin films is the current method used to achieve the required high-quality Ag coatings.…”

Section: Introductionmentioning

confidence: 99%

Highly Reflective Silver-Enhanced Coating with High Adhesion and Sulfurization Resistance for Telescopes

et al. 2022

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Highly reflective metal coatings are essential for manufacturing reflecting telescope mirrors to achieve the highest reflectivity with broad spectral bandwidth. Among metallic materials, enhanced silver-based coatings can provide higher reflectivity in the 400–500 nm spectral range to better performance from visible to near IR. Moreover, over-coating a dielectric protective layer on the mirror’s front side attains additional hardness and oxidation stability. In this paper, we study a combination of thermal and electron beam evaporation as a technology to form protected enhanced high reflective Ag coatings. A newly designed multiplayer film can pass ASTM 5B adhesive performance testing and give sulfurization inhibition. The average specular reflectivity for the enhancement coating is about 98% in wavelengths across the spectral range from 400–1000 nm. This innovation has been demonstrated on a Newtonian type telescope, with storage in an ambiance humidity H = 60–85%, and temperature T = 10–35 °C, for more than six months without degradation in coating performance.

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Reflectivity, polarization properties, and durability of metallic mirror coatings for the European Solar Telescope

Cited by 8 publications

References 0 publications

HIPPI-2: A versatile high-precision polarimeter

HIPPI-2: A versatile high-precision polarimeter

Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis

Highly Reflective Silver-Enhanced Coating with High Adhesion and Sulfurization Resistance for Telescopes

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