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Beam Divergence Calculator

Formula

The formula to calculate the beam divergence is:

$\theta = 2 \times \arctan \left( \frac{D_f - D_i}{2L} \right)$

Where:

$\theta$ is the angle of divergence
$D_f$ is the beam diameter at point f
$D_i$ is the beam diameter at point i
$L$ is the distance between point f and point i

What is Laser Divergence?

Laser divergence is the measure of the angle of a laser beam’s spread. A laser beam that has low divergence could be said to be “collimated”, which means it will maintain a narrow beam as opposed to spreading out. If you’re using an optical instrument, such as an optical collimator, that requires a collimated beam of light, you have to make sure that the laser beam has low divergence.

Example Calculation

Example:

Beam Diameter at Point f: 5 mm
Beam Diameter at Point i: 3 mm
Distance Between Points: 1000 mm

Calculation:

$\theta = 2 \times \arctan \left( \frac{5 - 3}{2 \times 1000} \right) = 0.11 \text{ degrees}$