Quarter-Wave Thickness

Quarter-wave optical thickness (QWOT): nd = λ/4. Optimal AR when nfilm = √(ninc·nsub).

Model: Exact

Quarter-wave thickness d = λ/(4n) = 99.6 nm

Optimal nfilm = √(ninc·nsub) = 1.233

R at design λ = 1.2601%

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

One lossless quarter-wave layer with constant indices at normal incidence on a semi-infinite substrate. R(λ₀) is a closed form and the spectrum a transfer matrix. Not modelled: dispersion, absorption, back surface.

  1. Macleod H. A. (2010). Thin-Film Optical Filters, 4th ed., ch. 2 and ch. 4 (single-layer antireflection coatings). CRC Press. doi:10.1201/9781420073034
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