This calculator will help you calculate the Beam diameter at focus, by inputting the $\frac{1}{e^2}$ spot diameter of the collimated Gaussian beam whose wavelength is $\lambda$. Together with the diameter of lens $D$ and the focal length $f$. In addition, by adding in the beam quality parameter $M^2$ into the formula will makes the output value more accurate.

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${2w_0}$= $\frac{4M^2 \lambda f }{\pi D}$

Input
Beam Diameter At Lens, $D$:
mm
Focal Length, $f$:
mm
Wavelength, $\lambda$:
mm
Beam Quality Factor, $M^2$:



Output
Beam Diameter At Focus, $w_0$:
mm