The curvature on the wavefronts is zero for the beam midsection and also methods zero as z → ±∞. It is equal to 1/R the place R(z) could be the radius of curvature like a operate of place together the beam, supplied by[1] A benefit to working with lasers http://riverkgbtm.fitnell.com/32362485/the-2-minute-rule-for-laser-optics