A Methodology for Correct Measurement of the Spatial-Energy Characteristics of Laser Beams

A methodology for correct measurements of the spatial-energy characteristics of laser beams is examined. This methodology is based on determining the initial moments of the spatial distribution of the intensity in a transverse cross section of the beam. A classification of the radiation fields involved in the measurement process is introduced: emitted, to be measured, and measured. It is shown that using the ISO document ISO 11146:2005, "Lasers and laser-related equipment. Test methods for laser beam widths, divergence angles and beam propagation ratios. Part 1–3," for measuring the spatial-energy characteristics of laser beams leads to incorrect measurement results. This happens because the recommendations for use of ISO 11146:2005 do not take into account the dynamic range of array radiation detectors, and the characteristics of the radiation field of interest to the user turn out to be divergent, which violates the unity of the measurements. Conditions that ensure convergence of the results are then practically unattainable. To solve these problems, it is proposed to establish and regulate the lower level of the dynamic range of the intensity measurement of the employed array detectors and examine the spatial-energy characteristics of the measurement field of interest to the user as a function of a set value of the lower level. It is shown that measurements by this method become correct and can be used to compare the characteristics of laser beams obtained with different array detectors. Formulas are given which take into account the effect of the lower level of the dynamic range of array detectors on the measurement results. These formulas should be recommended for inclusion in a revised edition of the national standard GOST R ISO 11146-2008, "Lasers and laser installations (systems). Methods for measuring widths, divergence angles, and propagation coefficients of laser beams. Parts 1–3".