How does beam divergence affect the visibility of a LASER?
A. LASER light beams are subject to divergence, which is measured in milliradians (mrad) or degrees. For many applications, a lower-divergence beam is preferable. Neglecting divergence due to poor beam quality, the divergence of a LASER beam is proportional to its wavelength and inversely proportional to the diameter of the beam at its narrowest point. For example, an ultraviolet LASER that emits at a wavelength of 308 nM will have a lower divergence than an infrared LASER at 808 nM, if both have the same minimum beam diameter. The divergence of good-quality LASER beams is modeled using the mathematics of Gaussian beams. LASERS used for astronomy purposes (“sky-pointing”) are designed so that the beam is visible to the naked eye located at the source of the beam for approximately 1 mile. After the beam has traveled a mile into the sky, to the user, it seems to end abruptly. This is the point where the human eye’s resolution can no longer resolve the beam; in effect, it “disappears”. Ho
