What is Single Longitudinal Mode
Within the laser community, one of the most overused and often miscommunicated terms is the phrase “single mode.” This is because a laser beam when traveling through air takes up a three-dimensional volume in space similar to that of a cylinder; and just as with a cylinder, a laser beam can be divided into independent coordinates each with their own mode structure. For a cylinder we would call these the length and the cross-section, but as shown in the figure below for a laser beam, we define these as the transverse electromagnetic (TEM) plane and the longitud… Read More