Laser beam spot size calculator

Input

Output

mm

About this calculator

This calculator computes the 1/e21/e^2 spot diameter of a collimated Gaussian beam whose wavelength is λ\lambda and diameter at lensDD when it is focused with a lens having a focal length ff. Additionally, the beam quality parameter M2M^2 can be specified if the beam deviates from an ideal Gaussian. With these inputs, the diameter of the focal spot is

2w0=4M2λfπD2w_0 = \dfrac{4 M^2 \lambda f}{\pi D}

To get this diffraction-limited beam diameter, the lens should not have strong aberrations. Additionally, the lens diameter should be at least twice the beam diameter input value not to clip the "wings" of the Gaussian profile.