🔭 Fabry-Pérot Interferometer

Explore resonance in an optical cavity: interference of multiply-reflected beams produces sharp transmission peaks. Adjust mirror reflectivity, cavity length, and refractive index to see how FSR, Finesse, and linewidth change.

Mirror reflectivity R 0.90

Cavity length L 500 nm

Refractive index n 1.00

Wavelength λ 550 nm

Finesse ℱ: 29.8

FSR: - nm

FWHM: - nm

T(λ): -

Order m: -

How it works

A Fabry-Pérot etalon consists of two parallel partially-reflecting mirrors separated by distance L. Light bounces back and forth; the transmitted beams interfere constructively when the round-trip optical path equals an integer multiple of the wavelength:

2nL = mλ (resonance condition)

Airy function: T(δ) = 1 / [1 + F·sin²(δ/2)] where F = 4R/(1−R)² is the coefficient of Finesse and δ = 4πnL/λ is the round-trip phase.

Finesse: ℱ = π√R / (1−R). Higher R → sharper peaks, higher spectral resolution.

FSR (Free Spectral Range): Δλ_FSR = λ² / (2nL). The spectral interval between consecutive resonance orders.

FWHM (linewidth): Δλ_FWHM = FSR / ℱ. Determines the minimum resolvable wavelength difference.