The Encyclopedia of Laser Physics and Technology states that "beam divergence of a laser beam is a measure for how fast the beam expands far from the beam waist, i.e., in the so-called far field." A laser beam with a low beam divergence is great for laser pointer devices. There are several measurement techniques including variable apertures, scanning pinholes, knife edges and CCD relays. An easy way to measure laser beams is with a beam profiler, that is, if you have a few thousand dollars lying around.
Things You'll Need
Laser beam White paper Ruler
Mount the laser solidly to a base. This can be as simple as setting a laser pointer on a table and taping it down.
Hang the white piece of paper on a wall directly across from the laser base about 3 meters away.
Shine the laser onto the white piece of paper.
Measure the diameter of the laser beam in millimeters where it exits the laser pointing device. The diameter is the distance across a circle.
Measure the diameter of the laser beam where it strikes the white piece of paper
Calculate the divergence of the laser beam. Divergence = 2arctan(Df-Di/2l). Df = second diameter measurement, Di = first diameter measurement, and l is = length in centimeters.