Resonator Mode Calculator

Analyze laser resonator stability, mode spacing, and beam waist for two-mirror cavities.

A two-mirror laser cavity is stable only when the g-parameter product g₁g₂ = (1 − L/R₁)(1 − L/R₂) lies between 0 and 1. This calculator takes cavity length, both mirror radii of curvature (or flat, R = ∞), and optional intracavity refractive index to compute the g-parameters, stability verdict, and named configuration (planar, confocal, hemispherical, or concentric). For stable cavities, it also returns the free spectral range Δν = c/(2nL), round-trip time, and — when a wavelength is provided — the fundamental TEM₀₀ intracavity beam waist w₀. Use it when designing a laser resonator, estimating mode spacing for etalon or injection-locking work, or verifying that a proposed mirror set is stable before purchasing optics.

Cavity Parameters
Enter cavity length and mirror radii to see resonator analysis.
Abridged Optics — Resonator Mode Calculator v1.0Assumes paraxial, empty (or uniformly filled) two-mirror cavity. Beam waist is for the fundamental TEM₀₀ mode.

All information, equations, and calculations have been compiled and verified to the best of our ability. For mission-critical applications, we recommend independent verification of all values. If you find an error, please let us know.