Explore the Thin-Film Interference Lab
Change a film's thickness and index and watch its reflected color shift, or find the exact quarter-wave thickness that cancels reflection.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
See it in action
The Thin-Film Interference Lab with sample data entered and the result showing.
What is the Thin-Film Interference Lab?
Change a film's thickness and index and watch its reflected color shift, or find the exact quarter-wave thickness that cancels reflection for anti-reflective coatings. It runs in your browser, so a change to a setting or a drag on an object shows up at once.
Camera lenses, eyeglasses and solar panels use engineered anti-reflective thin-film coatings, and the same physics explains the colors seen in soap bubbles and oil slicks on wet pavement.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
Thin-film interference happens because light reflects off both the top and bottom surfaces of a thin film, and those two reflections can add constructively or destructively depending on the extra path length.
The optical path difference is OPD = 2nt, where n is the film's refractive index and t is its thickness.
Anti-reflective coatings use a quarter-wave thickness, t = λ/(4n), to cancel reflection of a target wavelength by destructive interference.
Slide the thickness slowly and watch the reflected color swatch cycle.
Design a quarter-wave anti-reflective coating for green light.
Switch between the coating and soap-film cases and compare.
Used for
Pick one to see how it fits.
Physics learners
Physics students in middle school, high school and first-year university, teachers who want a quick demonstration for the projector, and anyone revising for exams.
Try it freeTeachers
For teachers: project the Thin-Film Interference Lab on the board, let students predict the result, then run it together and test this: Design a quarter-wave anti-reflective coating for green light. For students: change one thing at a time and write down what changes.
Try it freeHow it compares
A plain look at this tool next to the usual alternative.
| This simulation | Textbook diagram | |
|---|---|---|
| Interactive | Drag, tap and change settings | Fixed picture |
| Install | Nothing to install | Not needed |
| Cost | Free to use | Depends on the book |
Questions people ask
Why do soap bubbles show rainbow colors instead of one plain color?
The film's thickness varies slightly across the bubble and changes over time as it drains, and different thicknesses satisfy the constructive-interference condition for different wavelengths, so different colors reflect strongly at different spots.
How does a quarter-wave coating stop reflections?
At thickness t = λ/(4n), the light reflecting off the bottom surface travels an extra half-wavelength compared to the top reflection, so the two reflected waves arrive out of phase and cancel by destructive interference.
Is the Thin-Film Interference Lab free to use?
Yes. The Thin-Film Interference Lab is free, needs no signup or download and runs in your web browser. It is part of the Physics group of AZRS simulations.
Does the Thin-Film Interference Lab work on a phone or tablet?
Yes. The Thin-Film Interference Lab takes touch input as well as mouse input, so you can use its 4 adjustable settings with a finger. A larger screen makes the controls and graphs easier to read.
How do I use the Thin-Film Interference Lab?
1. In the Thin-Film Interference Lab, use the controls to change Case, Film thickness t, Film refractive index n, Wavelength λ. The simulation reacts instantly. 2. In the Thin-Film Interference Lab, pick an option such as Anti-reflective coating (1 phase shift), Soap film in air (1 phase shift, symmetric) to switch modes or load an example. 3. Start with this experiment: Slide the thickness slowly and watch the reflected color swatch cycle. Drag any glowing handle, object or slider with your mouse or finger and the Thin-Film Interference Lab responds in real time. 4. Change one setting at a time and watch which readout moves, then compare it with this idea: Thin-film interference happens because light reflects off both the top and bottom surfaces of a thin film, and those two reflections can add constructively or destructively depending on the extra path length.
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