Beam Quality Calculator
Calculate focused spot size, Rayleigh range, divergence, and irradiance for real beams with M² correction.
Real laser beams diverge faster than the diffraction limit by a factor M² (M-squared), which enters the propagation equations as w(z) = w₀ √(1 + (z/z_R)²) where the Rayleigh range z_R = π w₀² / (M² λ). M² = 1 for an ideal TEM₀₀ beam; values above 1.1–1.2 are typical for single-mode diode and fiber lasers, and higher for multimode or aberrated beams. This tool has two modes. Free Propagation computes Rayleigh range, full divergence angle, beam radius at a specified distance, and peak irradiance, comparing the real beam against the M² = 1 ideal. Focused Beam computes the 1/e² focused spot radius and depth of focus at a lens, given input beam radius, focal length, and M². Beam parameter product (mm·mrad) is also reported.