# Laser beam spot size calculator

Input

Output

mm

### Try also:

Mode field diameter calculator

This calculator computes the $1/e^2$ spot diameter of a collimated Gaussian beam whose wavelength is $\lambda$ and diameter at lens$D$ when it is focused with a lens having a focal length $f$. Additionally, the beam quality parameter $M^2$ can be specified if the beam deviates from an ideal Gaussian. With these inputs, the diameter of the focal spot is
$2w_0 = \dfrac{4 M^2 \lambda f}{\pi D}$