Why a small change in this specification greatly affects laser beam intensity.
Divergence is the increase in laser beam diameter with distance from the aperture from which the beam emerges in any plane that intersect the beam axis.
What this means is that the diameter of the beam expands over distance at an angle (the divergence in milliradians or mrad ). As this angle increases, (even by small amounts) the diameter of the beam increases and the area of the beam (Area of a circle = π multiplied by the square of the radius) increases at an exponential rate.
Optotronics handheld laser products have a divergence spec. of 1.2mrad orless (unless otherwise noted).
Most other suppliers of handheld laser products have a divergence spec. of 1.5mrad.
This means that for the same beam diameter and output power, the light intensity or irradiance (Output power / area of beam spot) is up to 56% greater with a divergence of 1.2mrad vs 1.5mrad.
So with an Optotronics laser your not only getting more for your money, your getting a beam that's 14.8% more intense at 0.50 meters distance to over 55% more intense at distances of greater than 60 meters.
Below is a chart showing the divergence for a 260mW laser with a 1.5mm beam diameter and a distance of 3 meters vs. an Optotronics portable RPL with a divergence of less than 1.2 mrad.
(click the chart to download the Excel sheet to experiment with the divergence / irradiance calculators for various senarios).