Residual distortions caused by the size of a reference source

Abstract

An adaptive focusing of a laser beam through a turbulent atmosphere is investigated. We consider the reference source with a random position (fluctuations of the position of the center of gravity) on the object onto which laser radiation is focused. The problem of focusing of coherent optical radiation through the atmosphere can arise in practice when energy is transported to a sufficiently large remote object by laser radiation. The reference source can be formed by radiation reflected from the object to which coherent laser radiation should be focused. The methods used for determining the phase on the basis of coherent and non-coherent reference radiation were described early. The analytical calculated are performed. Distributions of the mean intensity of the field of a coherent laser beam focused in a turbulent medium by means of adaptive phase correction with the use of a point reference source with random center are calculated. The laser beam focused with the use of adaptive correction by the phase conjugation algorithm and the reference source is a spherical wave with a fluctuating radiation center. The distribution of the mean intensity of the focused coherent radiation beam is studied on the basis of the Huygens–Fresnel principle. The approach considered here can be used in cases with both coherent and non-coherent illumination. In this work, we made an attempt to estimate the efficiency of adaptive focusing of coherent laser radiation from the viewpoint of energy concentration and transfer. The Strehl ratio is used as the parameter of efficiency. Results of adaptive focusing with moving and motionless reference sources are compared. It is demonstrated that a point reference source with a random position of the center can be an effective tool for adaptive focusing of radiation beams.