Laser beam divergence describes the rate at which a laser beam spreads as it travels away from its source. It is an important characteristic when evaluating how laser radiation behaves over distance.

A beam with low divergence can remain concentrated over a relatively long distance, while a beam with greater divergence spreads more quickly. However, divergence does not automatically make a laser safe to view.

Even a relatively small beam can contain enough optical energy to cause serious eye injury. The human eye can also focus certain laser wavelengths onto a very small area of the retina, significantly increasing the potential for damage.

When evaluating laser hazards, beam divergence should therefore be considered alongside wavelength, power, beam diameter, operating mode, and exposure conditions.

Laser safety eyewear should be selected according to the actual laser specifications. The filter needs documented protection at the wavelength being used, with an appropriate optical density for the expected hazard.

Beam containment, barriers, controlled access, and safe operating procedures should also be used wherever appropriate. Laser safety glasses are an important protective measure but should not be treated as the only control.

Understanding beam divergence helps laser users recognize why distance and apparent beam size are not sufficient on their own to determine whether a laser is safe.