Optical system contamination: formation of films and droplets

Luey, Kenneth T.; Olson, Keith R.; Coleman, Dianne J.

doi:10.1117/1.jatis.4.3.036001

Cited by 10 publications

(3 citation statements)

References 22 publications

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“…Consequently, in addition to water ice, tetramethyl-tetraphenyl trisiloxane (DC-704) was included in the model as a silicone contaminant analog, the photochemical deposition of which has been commonly studied 25 – 27 DC-704 has been shown to deposit as a smooth, widely-spread film on nonmetallic, cold surfaces for temperatures up to 93K due to inadequate thermal energy to induce the coalescence of molecules 28 . Moreover, in a recent study conducted for JWST, DC-704 was identified to be one of the primary potential contaminants, with its origin attributed to silicone fluids used in diffusion pumps for high vacuum systems 29 …”

Section: Methodsmentioning

confidence: 99%

“…[25][26][27] DC-704 has been shown to deposit as a smooth, widely-spread film on nonmetallic, cold surfaces for temperatures up to 93K due to inadequate thermal energy to induce the coalescence of molecules. 28 Moreover, in a recent study conducted for JWST, DC-704 was identified to be one of the primary potential contaminants, with its origin attributed to silicone fluids used in diffusion pumps for high vacuum systems. The contaminant assumed to deposit onto the surface first is expected to be the nvr, DC-704.…”

Section: Environmental Changes In Spacementioning

confidence: 99%

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Extreme broadband dichroics: Monte Carlo transmission line modeling for astronomical spectroscopy

Thurairethinam,

Savini,

Hawkins

et al. 2024

J. Astron. Telesc. Instrum. Syst.

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Dichroic beamsplitters, or dichroics, rely on the optical interference that occurs within thin-film layers to ensure the separation of the transmission and reflection of selective wavelengths of an incident beam of light at a given angle of incidence. Utilized within the optical systems of numerous space telescopes, they act to separate the incoming light spectrally and spatially into various channels. As space missions increasingly demand simultaneous observations across wavebands spanning extreme wavelength ranges, the necessity for exceedingly complex broadband dichroics has emerged. Subsequently, the uncertainties pertaining to their optical performance have also become more intricate. We use transmission line modeling to evaluate the spectral performance of multilayer coatings deposited on a substrate material for given thicknesses, materials, angles of incidence, and polarization. A dichroic recipe in line with the typical specifications and requirements of a dichroic is designed with the aid of a Monte Carlo simulation. The tolerances of the coating performance to systematic and random uncertainties from the manufacturing process, as well as from environmental changes in space, are studied. With the aid of accurate manufacturing recipes and uncertainty amplitudes from commercial manufacturers, this tool can predict variations in the optical performance that result from the propagation of each of these uncertainties for various hypothetical scenarios and systematic effects.

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Section: Methodsmentioning

confidence: 99%

Section: Environmental Changes In Spacementioning

confidence: 99%

Extreme broadband dichroics: Monte Carlo transmission line modeling for astronomical spectroscopy

Thurairethinam,

Savini,

Hawkins

et al. 2024

J. Astron. Telesc. Instrum. Syst.

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“…On ground, contamination is an inherent part of construction and launch, and subject to contamination control plans (Kimoto 2017;Luey et al 2018;Patel et al 2019;Abeel et al 2022). In the vacuum of space, contamination is driven by material outgassing (Chiggiato 2020).…”

Section: Introductionmentioning

confidence: 99%

Euclid preparation

Schirmer¹,

al.²

2023

A&A

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Material outgassing in a vacuum leads to molecular contamination, a well-known problem in spaceflight. Water is the most common contaminant in cryogenic spacecraft, altering numerous properties of optical systems. Too much ice means that Euclid’s calibration requirements cannot be met anymore. Euclid must then be thermally decontaminated, which is a month-long risky operation. We need to understand how ice affects our data to build adequate calibration and survey plans. A comprehensive analysis in the context of an astrophysical space survey has not been done before. In this paper we look at other spacecraft with well-documented outgassing records. We then review the formation of thin ice films, and find that for Euclid a mix of amorphous and crystalline ices is expected. Their surface topography – and thus optical properties – depend on the competing energetic needs of the substrate-water and the water-water interfaces, and they are hard to predict with current theories. We illustrate that with scanning-tunnelling and atomic-force microscope images of thin ice films. Sophisticated tools exist to compute contamination rates, and we must understand their underlying physical principles and uncertainties. We find considerable knowledge errors on the diffusion and sublimation coefficients, limiting the accuracy of outgassing estimates. We developed a water transport model to compute contamination rates in Euclid, and find agreement with industry estimates within the uncertainties. Tests of the Euclid flight hardware in space simulators did not pick up significant contamination signals, but they were also not geared towards this purpose; our in-flight calibration observations will be much more sensitive. To derive a calibration and decontamination strategy, we need to understand the link between the amount of ice in the optics and its effect on the data. There is little research about this, possibly because other spacecraft can decontaminate more easily, quenching the need for a deeper understanding. In our second paper, we quantify the impact of iced optics on Euclid’s data.

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