No abstract

ing the receiver aperture include a contribution not only from the density fluctuations but also from fluctuations of the transverse size of the beam ("breathing") and spatial wandering of the beam. T In the case of a Gaussian distribution of the intensity in the transverse section through the beam we may expect the fluctuations due to the "breathing" of the beam to decrease more slowly with increasing receiver aperture than the other .two factors. For realistic limits of the "breathing," these fluctuations affect considerably the distribution law of the signal for D~ A. When the receiver aperture is increased still further, the relative importance of the fluctuations due to the "breathing" of the beam decreases. If the aperture is sufficiently large so that it covers the whole beam (D »A), the spatial wandering and "breathing" of the beam have practically no influence on the distribution. CONCLUSIONSWhen fluctuations in an atmospheric path are saturated, the parameters of the fluctuations in laser beams of 0.63 and 10.6 M wavelengths differ only slightly when recorded using the same receiving-transmitting optical channel. Theoretical advantages of the use of the 10.6 M radiation in communication systems 8 are unfortunately found to be of very little significance in practical communication under conditions of saturation of the intensity fluctuations.An analysis is made of two systems for compensating birefringence induced in an active element when thermal stresses in the element have a longitudinal symmetry plane. Simple passive anisotropic elements are used in both systems. The Jones matrix method is used to demonstrate that these systems, together with thermally stressed active elements, are equivalent to a half-wave phase plate. An estimate is obtained of the influence of a thermal lens formed in an active element on the birefringence compensation process. Experiments proving the feasibility of the systems are reported. A periodic double-pass amplifier based on these systems is proposed.