The spectral-absorptance curves of quarter-wave reflectors are quite asymmetric in general as a result of absorption in the layers. The maximum electric field E in an infinite stack is in the center of the high-index (low-index) layer at the low-frequency (high-frequency) end of the high-reflection band. Thus, the absorptance minimum of a stack having much greater absorption in the high-index material occurs at ω > ωc (band center). Operation at ω > ωc could increase the damage resistance if the high-index material is easily damaged. At ωc, E decays rapidly. As ω departs from ωc in an infinite reflector, E penetrates deeper into the coating, with no decay at the band edges. The peak-to-peak distance in an infinite dielectric stack is constant for all frequencies in the band. By using the continuity of E and dE/dz, E can be obtained from E = 0 at the metallic substrate or, in an infinite stack, from E = 0 at the reflector surface for ω = ωc or E = 0 in the center of the high- or low-index layer at the band edges. Simple closed-form approximations for the spectral absorptance and the phase of E are accurate and sufficient for present applications.
© 1979 Optical Society of AmericaFull Article | PDF Article
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