that all beam profiles — Gaussian, flat top, TEMxy, or any shape — must follow the equation above provided that the beam radius uses the D4σ definition of the beam width. Using other definitions of beam width does not work. In principle, one could use a single measurement at the waist to obtain the waist diameter, a single measurement in the far field to obtain the divergence, and then use these to calculate the BPP. The procedure above gives a more accurate result in practice, however. High-power lasers, such as those used in laser welding and cutting are typically measured by using a beamsplitter to sample the beam. The sampled beam has much lower intensity and can be measured by a scanning-slit or knife-edge profiler. Good beam quality is very important in laser welding and cutting operations. See also Etendue List of laser articles References Further reading Laser science