Abstract
Black paints are commonly used to provide broadband light absorbers in high-precision optics. We show how multidielectric coatings improve the performances of these absorbers. The coated rough paints still exhibit a quasi-lambertian diffuse reflection, but this scattering pattern can be reduced by several orders of magnitude, which strongly enhances absorption. Predictions are based on an exact electromagnetic theory of light scattering from arbitrary rough multilayers. Results are also compared to useful approximate theories.
Highlights
Light absorbers are commonly required to cancel or reduce parasitic light in optical systems [1,2,3,4,5,6,7,8,9,10,11,12]
We consider a three homogeneous media problem where the layer Ω2 is bounded by two non-intersecting rough surfaces Σn with equations z = zn + hn(r) for n = 1, 2 in the Cartesian coordinates (x, y, z), and denoting (x, y) = r (Fig. 1)
Using an exact electromagnetic theory of light scattering from arbitrarily rough surfaces, we have shown that multilayer AR optical coatings hold their interferential properties when deposited on rough surfaces which scatter light in a lambertian way
Summary
Light absorbers are commonly required to cancel or reduce parasitic light in optical systems [1,2,3,4,5,6,7,8,9,10,11,12]. Different techniques [1,2,3,4,5,6,7,8,9,10,11,12] can be used to produce such devices, and surely the most classical is to coat a smooth (polished) absorbing substrate with dielectric anti-reflective layers In this case the design of the multidielectric coating can be optimized and drives the absorber performance. For that reason the theory is implemented with the Method of Moments (MoM) for two-dimensional scattering (one variable surface topography) [31], and the rough multilayer is illuminated with a tapered wave (a Gaussian beam), under S- or P-polarization [27] With this theoretical tool, we analyse the angular and spectral performances of light absorbers made with different multilayered antireflection coatings deposited on black paints.
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