It has been pointed out that the two terms effective scattering volume and laser guide star are scientific synonyms. The first term was introduced by the end of 1970 by specialists in atmospheric optics and laser sounding. Information has also been given concerning fluctuations of waves reflected from an object and waves passed twice through atmospheric inhomogeneities. A corresponding mathematical apparatus allows one to estimate correlation characteristics of a laser guide star. The mutual correlation function of random angular displacements of a plane-wave image and the centroid displacements of a focused Gaussian laser beam are considered. The algorithm of optimal correction is introduced in which a priori information is used. Based on this algorithm, the variance of residual jitter of a star image obtained with the use of a laser guide star is evaluated.