Laser Beam Divergence Calculator

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Gaussian mode uses beam optics physics. Geometric mode uses two measured beam diameters at a known separation distance.
Wavelength of the laser in nanometres. Common values: HeNe 633 nm, Nd:YAG 1064 nm, CO2 10600 nm, blue diode 445 nm.
nm
The 1/e² intensity diameter at the waist (minimum focus point). For beam waist radius w₀, enter 2w₀.
mm
M² = 1 for a perfect TEM₀₀ Gaussian beam. Real lasers range from about 1.1 (single-mode fiber) to 10+ (multimode high-power). Increases divergence and reduces focusability.
Distance from the beam waist at which to evaluate the beam radius w(z). Leave at 0 to see the waist-plane result.
m
Choose the unit for divergence angles in the results.
Divergence half-angle (θ)Near-diffraction-limited
0.4023

Half-angle of the full divergence cone (from beam axis to 1/e² edge)

Full cone angle (2θ)0.8047
Angle unitmrad
Rayleigh range (zᴿ)1.243m
Confocal parameter (b)2.485m
Beam radius at z4.054mm
Beam diameter at z8.109mm
Beam Parameter Product (BPP)0.2012mm·mrad
Diffraction-limited BPP (λ/π)0.2012mm·mrad
0.4023 mrad
Highly collimated<1Good collimation1-5Moderate divergence5-20High divergence20+

Divergence half-angle: 0.4023 mrad

  • Rayleigh range: 1.243 m. Inside this distance the beam stays nearly collimated; beyond it the beam expands roughly linearly.
  • Beam Parameter Product is 0.2012 mm-mrad. This gives M² = 1.00: near-perfect, single-mode Gaussian quality.
  • At 10 m from the waist, the beam 1/e² diameter is 8.109 mm.

Next stepUse the propagation distance input to see how the beam size evolves at your working distance.

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