Thin Film Interference Calculator
Enter film thickness, refractive index, and wavelength to find whether reflected or transmitted light undergoes constructive or destructive interference.
Use the Thin Film Interference Calculator
Film Parameters
Soap film: ~100–1000 nm; AR coating: ~100–200 nm
Glass ≈ 1.5 · Water ≈ 1.33 · MgF₂ ≈ 1.38
Air/vacuum = 1.0 · Same on both sides assumed
Visible: 380–700 nm (green ≈ 550 nm)
Phase Shift Analysis
Top Surface
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Bottom Surface
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Reflected Light
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Nearest constructive λ
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Nearest destructive λ
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Transmitted Light
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Nearest constructive λ
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Nearest destructive λ
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Optical Path Difference
OPD = 2 n t
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OPD / λ (ratio)
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Constructive Wavelengths for Reflected Light (orders m = 0–5)
| Order (m) | λ constructive (nm) | λ destructive (nm) | Visible? |
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Enter film parameters above and click Calculate.
Summary
Enter film thickness, refractive index, and wavelength to find whether reflected or transmitted light undergoes constructive or destructive interference.
How it works
- Enter the film thickness in nanometers.
- Enter the refractive index of the film (e.g. 1.5 for glass, 1.33 for water).
- Enter the wavelength of incident light in nanometers.
- Select the surrounding medium (air/vacuum or a custom refractive index).
- Click Calculate to see whether reflected and transmitted light interfere constructively or destructively, along with the nearest constructive and destructive wavelengths.
Use cases
- Predict the colors seen on soap bubbles and oil slicks.
- Explore constructive and destructive interference for a film surrounded by the same medium on both sides.
- Analyze thin-film optical filters and beamsplitters.
- Solve optics homework problems involving phase shifts at boundaries.
- Compare reflected and transmitted interference orders for a symmetric thin-film model.
- Explore how iridescence works in butterfly wings and beetle shells.
Frequently Asked Questions
Last updated: 2026-09-22 ·
Reviewed by Nham Vu