A precise approach to determining the optimum location of observation plane or optimum size of array aperture to achieve maximum power-in-the bucket in the coherent beam combining

Abstract

The power-in-the bucket and the intensity distribution generated by the coherent combination of a definite number of similar laser beams with Gaussian profiles are numerically studied at different observation planes in the far-field. A precise method is introduced for optimal engineering of the array aperture size and the observation plane location in the far-field. A relation between the array aperture size and the observation plane distance is proposed using the Fresnel zone concept for coherent beam combining to achieve the maximum power-in-the bucket (PIB). The results reveal that the maximum PIB in a small bucket radius of 5 or 10 cm in the observation plane (radii in directed-energy applications) can be obtained either when the observation plane is located at the primary region of the far-field for a specified array aperture size or when the array aperture size is equal to or less than the size of the first Fresnel zone . Also, the proposed approach is independent of array geometry so that it will be practical for different array geometries, namely square, circular, and hexagonal. Furthermore, it is also independent of other parameters such as numbers and divergence of beams. The maximum amount of PIB in a specified observation plane location can be obtained for array aperture sizes lower than the first Fresnel zone, regardless of the number of beams or their waist radius.