Calculation and measurement of scattering for investigation of microroughness in optical coatings

We propose a novel interpretation of stray light, which is modeled using a scattering process. For this, a description and simulations based on the bidirectional scattering distribution function ͑BSDF͒ are developed. We focus on the particular example of a window closing an optical cavity. Such a window is known to introduce a stray light component that is experimentally very subtle to handle. Our idea is motivated by the uncomfortable observation that for years, the usual estimation of this parasitic contribution ͑be it for absolute or relative measurements, for visible or IR applications, for field or laboratory experiments, etc.͒ was based on the rather imprecise and obviously incorrect assumption ͑nev-ertheless today a widely used rule of thumb͒ that the optical window can be approximated by a graybody emitting in its transparency range. This statement obviously goes against Kirchhoff's law of radiation, and can thus not be physically sound. Various typical experimental situations are explored with our model, and a comparison is made with results given by the rule of thumb. This shows some cases of relative concordance. However, the scatter-based model should provide an individually more accurate estimation, as shown by some examples.

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Role of interface correlation in light scattering by a multiplayer

Amra¹,

Apfel

Pelletier³

1992

Appl. Opt.

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Four industries prepared optical coatings with a common design that permits an easy determination of cross-correlation laws between the rough interfaces in the stack. Different pairs of materials and deposition processes were used. After clarifying the differences between scalar and vector theories of light scattering caused by rough interfaces in optical multilayers, we compare the experimental values with both theories. Factors such as variations of correlation with spatial frequency, residual roughness, and slight errors in the design are taken into account for comparison with the vector theory of angular scattering. Correlation of the interface roughnesses is found to be high for practically all coatings. However, at low scatter-loss levels, scattering by localized defects in the coatings appears to dominate over the scattering caused by rough interfaces.

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Calculation and measurement of scattering for investigation of microroughness in optical coatings

Cited by 9 publications

References 17 publications

Optical characterization of photochromic effect

Optical characterization of photochromic effect

Scatter-based interpretation of infrared stray light from warm windows in optical instruments

Role of interface correlation in light scattering by a multiplayer

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