1 October 1997 Scaling rules for quintic refractive index matching semi-infinite-band antireflection coatings
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An inhomogeneous refractive index layer that follows a specific quintic (fifth-order polynomial) profile that smoothly matches the two-media interface is known to drastically reduce the nominal Fresnel reflection at this interface. There is so short wavelength cutoff for a quintic (or quintic-like) layer, as the reflectance continues to decrease with decreasing wavelength. Thus the quintic matching layer is a semi-infinite band antireflection coating. Furthermore, at the long wavelength end of the spectra the reflectance never rises above that of the Fresnel reflection at the bare interface, a feature not shared by multilayers optimized over specific bandwidths. A scaling relationship that relates the long wave cutoff of the total optical thickness of the quintic layer needed for a given reflectance level and for a given difference in media refractive index is described. For example, a quintic layer whose optical thickness is two waves or four halfwaves (at the longest wavelength of the band) will reflect at least four orders of magnitude less than the reflectance of the bare interface for all lower wavelengths. This paper also compares a quintic layer which is inhomogeneous to a needle-optimized multilayer design.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
William H. Southwell, William H. Southwell, } "Scaling rules for quintic refractive index matching semi-infinite-band antireflection coatings", Proc. SPIE 3133, Optical Thin Films V: New Developments, (1 October 1997); doi: 10.1117/12.290202; https://doi.org/10.1117/12.290202

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