AR Coating Thickness Calculator
Single-layer quarter-wave anti-reflection design: film thickness t = λ₀ / 4n₁, ideal index n₁ = √(n₀nₛ), and the resulting reflectance spectrum.
- Quarter-wave thickness
- 194.7 nm
- Ideal film index √(n₀nₛ)
- 1.865
- R at λ₀, uncoated
- 30.64 %
- R at λ₀, coated
- 0.416 %
Note: this film’s index is above the ideal √(n₀nₛ). A quarter wave still minimizes reflectance at λ₀, but the residual R shown is the floor for this material. A lower-index film (or a two-layer design) gets closer to zero.
Assumptions: normal incidence, lossless and non-dispersive indices, single layer. Real coatings shift with angle (the effective optical thickness shrinks as cos θ inside the film) and with material dispersion. Treat results as the starting design, not the deposition recipe.
For the physics behind the quarter-wave condition and multi-layer designs, see the companion article Anti-reflection coating design and the AR coating glossary entry.
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