The problem of correct measurements of the width and diverge angle of a laser beam

Using examples of known spatial distributions of intensity in the cross section of a laser beam in the plane of the emitter, formulas for the measurement error of the second moments in the far zone by a matrix radiation detector associated with determining the beam width and divergence angle using the existing standard ISO 11146: 2021 “Lasers and laser-related equipment. Test methods for laser beam widths, divergence angles and beam propagation ratios, Part 1-2”. Gaussian, exponential and uniform spatial intensity distributions in the emitter plane are considered. It is shown that the use of the mentioned standard leads to incorrect measurements due to the divergence of the measured value. In this case, the conditions ensuring the convergence of results are practically impossible to fulfill. Recommendations for the measurement process are proposed that eliminate the noted drawback. Key words: metrology of laser radiation, measurement methods, moments of intensity distribution, matrix radiation receiver, laser beam width, divergence angle.