A free, in-browser Gaussian beam calculator for designing real laser systems — fiber collimation, beam expanders, telescopes, and focusing optics. It propagates a laser beam through lenses, fibers, and apertures using the complex beam parameter and ABCD matrices, and solves for whichever parameters you leave free: fix the beam you want and it finds the focal lengths and spacings that produce it.
The core relations it evaluates: the Rayleigh range zᵣ = π w₀² / λ, the far-field divergence θ = λ / (π w₀), and the beam radius w(z) = w₀ √(1 + (z/zᵣ)²), for an ideal TEM₀₀ beam. Full derivations and design formulas are in the guides below.
Use it as a Rayleigh range calculator, beam waist calculator, laser beam divergence calculator, and Gaussian beam propagation workbench. You can enter waist radius or fiber mode field diameter, switch units directly in the table, include real beam quality with M², and propagate the beam through free space, thin lenses, mirrors, interfaces, and apertures.
Unlike a single-formula calculator, the solver can work backward from design goals: lock a target waist, output collimation, lens spacing, focal length, or beam radius, then leave the unknown parameters free and let the constraint solve produce a physically consistent optical layout.