Protected Silver Mirror
Protected silver coating — high reflectance from the visible to the IR with dielectric overcoat and adhesion layer.
Mean R, 400–700 nm
96.19 %
Without overcoat: 97.58 %
Mean R, 700–1200 nm
98.73 %
Minimum in 400–700 nm: 90.11 %
Lowest R, 300–1200 nm
3.81 %
at 304 nm
Silver model
Ag uses the n, k Yang et al. (2015) measured on template-stripped silver, which include the interband edge: R falls to about 5 % near 310 nm and is under 80 % below about 345 nm, so silver is a poor UV mirror. The overcoat and adhesion layers are lossless with constant indices; under opaque Ag (≳ 50 nm) the adhesion layer hardly matters. Exact transfer matrix, normal incidence, back face ignored. Template-stripped silver is the best case: evaporated and sputtered films reflect a little less, and much less once they tarnish.
Model and references
Exact. The equations are exact within the stated assumptions, or are a standard's tabulated values. The results are as good as the inputs. About the tiers
Transfer matrix at normal incidence: overcoat, Ag and adhesion layer on the substrate. Ag from Yang et al. 2015 (template-stripped, the best case); dielectrics lossless with constant n.
- Yang H. U., D'Archangel J., Sundheimer M. L., Tucker E., Boreman G. D., Raschke M. B. (2015). Optical dielectric function of silver. Phys. Rev. B 91, 235137. doi:10.1103/PhysRevB.91.235137
- Macleod H. A. (2010). Thin-Film Optical Filters, 4th ed., ch. 5 (protected metal mirrors). CRC Press. doi:10.1201/9781420073034