Inoptics, atophat beam (alsoFlat-top[1] ortop-hat beam) such as alaser beam or electron beam has a near-uniformfluence (energy density) within a circular disk. It is typically formed byrefractive[2] ordiffractive optical elements from aGaussian beam. Tophat beams are often used in industry, for example forlaser drilling of holes inprinted circuit boards. They are also used in very high power laser systems, which use chains ofoptical amplifiers to produce an intense beam. Tophat beams are named for their resemblance to the shape of atop hat.
Due todiffraction, a beam cannot maintain a sharp-edged tophat cross-section for more than a short distance of propagation, and the edges of the distribution will become increasingly fuzzy as the beam propagates forward.[1]