Skip to content
ENExplore Calculators

Thin Film Interference Calculator

Work out thin film interference instantly with clear inputs, formula shown and shareable results.

About Thin Film Interference Calculator

Light reflected from the two surfaces of a thin film interferes. Reflection at the front surface flips the phase by half a wavelength, so constructive reflection needs 2nt = (m + 1/2)lambda while cancellation needs 2nt = m.lambda. A 400 nm soap film at n = 1.33 reinforces around 709 nm, giving it a reddish sheen.

Formulas

Constructive reflection

2 n t = (m + 1/2) lambda

Destructive reflection

2 n t = m lambda

Worked example

With the default values below, Thin Film Interference Calculator returns Wavelength Reinforced In Reflection of 709.333. Change any input above and every figure here is recalculated in your browser.

Inputs used

Film thicknessminimum 0 nm
400 nm
Refractive index of the filmminimum 0
1.33
Interference order mminimum 0
1

Results

Wavelength Reinforced In Reflection
709.333 nm
Wavelength Cancelled In Reflection
1,064.000 nm
Optical Path Difference
1,064.000 nm
Visible Effect
Reinforced colour falls in the visible band

Step by step

  1. 1Values used
  2. 2Constructive reflection
  3. 3Destructive reflection
  4. 4Wavelength Reinforced In Reflection= 709.333 nm
  5. 5Wavelength Cancelled In Reflection= 1,064.000 nm
  6. 6Optical Path Difference= 1,064.000 nm
  7. 7Visible Effect= Reinforced colour falls in the visible band

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is there a half-wavelength shift?

Reflection off a medium of higher index inverts the wave. Only the front surface does this here, so the two reflections start half a cycle apart.

Is this why anti-reflection coatings work?

Yes. A quarter-wave layer of the right index makes the two reflections cancel, which is how camera lens coatings suppress glare.

Related Calculators

Thin Film Interference Calculator | Calcrivo