# LASERCALCULATOR

Input

Output

μm²

sr

$R = \dfrac{P}{A\Omega}$
where $P$ is the optical power, $A$ is the cross-sectional area of the focal spot or the core area of the fiber, and $\Omega$ is the beam's divergence solid angle defined by its NA. This calculator computes $\Omega$ as
$\Omega = 2\pi \left(1-\cos\theta\right)$
where $\theta = \arcsin(\mathrm{NA})$ is the divergence angle. For small NA values, a useful approximation formula is
$\Omega = \pi \mathrm{NA}^2$