= Spectral colour of an antireflection coating
A thin-film design that suppresses reflected green light more strongly than red and blue can leave a purple residual <reflection>. A single quarter-wave layer cancels <reflections> exactly only at its design <wavelength> and angle under the ideal index-matching condition. <reflection> colour should be distinguished from the much smaller colour change of the transmitted beam; multilayer designs can broaden the low-reflectance band.
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