Beam diameter and beam divergences are two of the most important technical specifications to consider when choosing a laser.
Obviously beam diameter is just the diameter of a laser beam, measured in millimeters. Beam divergence measures how much the laser beam expands per meter. For example, a laser with a beam divergence of 1.0mRad will have a beam that expands 1.0mm per meter.
How do these two specs relate to each other? and more importantly, why does it matter?
It all comes down to how small the end "spot"(the diameter size of your leaser beam) is at certain distances. This is important because you want to point far, far away and because you want to burn stuff, lots of stuff.
Common senses tell us that if a laser beam diameter is small, it can go further and burn with more power than if it is big. Ideally, we want to have small beam diameter at aperture AND small beam divergence.
There is a small catch though. As nature always plays with humans so that we don't get something for nothing, you can't have both a small beam diameter and a small beam divergence. According to the Laws of Photonics, these two specifications have an inverse relationship; if one increases, the other must decrease.
A detailed example should help clear everything up. Let's say we have a Nexus 95 (Executive Series) and an Evo 95. Check the little table at the top of the page. We know that the Nexus has a beam diameter of 1.6mm at aperture and a beam divergence of 1.0mRad. The specs for the Evo 95 are 0.8mm and 1.5mRad respectively.
At aperture, the diameter of the Evo 95mW is only one half that of the Nexus 95mW. At equal power output, the EVO 95mW actually has four times more burning power than the Nexus 95mW (burning power is proportional to area, which is proportional to the square of the diameter)!
However, at a distance of two meters, the beam diameter of the Nexus 95mW and the Evo 95mW are nearly identical; the burning capabilities are also nearly identical. At five meters, the Nexus actually has the smaller beam diameter (8.3-6.6 = 1.7mm, still not quite noticeable though). The conclusion here is that the Executive Series is better for long distance pointing as its beam will grow slower with distance.
The Evolution Series, while maintaining a decent performance at far range pointing, is designed for burning power up close.
Click on the laser models above to see the characteristics for each individual laser. Compare and contrast to see which is most suitable for you!
*If you are confused by the Pulsar's negative beam diameter, the following is a brief explanation. The -4.5mm beam diameter is actually just 4.5mm (the absolute value of -4.5mm). Why negative? The Pulsar Series is unique. Its beam diameter actually decreases right after it leaves the aperture before it increases again. All other lasers we carry have beams expanding right off the laser lens.