Use of dynamic holography technique for correction of aberrations in telescopes

Imaging of remote objects from space with the use of high-spatial resolution telescopes is a vital problem for a number of applications. Enlarging the primary mirror diameter aimed at increasing the telescope resolution is limited, on the one hand, by a dramatic growth of its cost with diameter, and on the other by the complexity and cost of a system that is necessaiy to maintain the mirror shape with high accuracy in realistic conditions of thermal and gravitational loads. Recently various adaptive techniques for correction of static and dynamic aberrations in telescopes have been developed. They allow in principle to enlarge the primary mirror due to the use of multisegment constructions when separate segments are phased to achieve the ultimate system resolution determined by the priinaiy mirror diameter. However, all these techniques, based on the use of beam wavefront analyzers, active minors with a lot of actuators and control electronics, are rather sophisticated and limited in response time, the number of actuators and of segments to be phased. For this reason, in parallel with traditional adaptive optic techniques some other approaches to the problem, based on the use of nonlinear optics techniques, have been progressing last years. One of the promising solutions for high-resolution imaging with the use of poor - quality optics is based on illumination of remote objects by laser radiation and their observation in reflected coherent light 2, It gives the opportunity to apply phase conjugation (PC) techniques, developed for coherent laser radiation, for correction of aberrations of the segmented mirror. The correction concept uses such a design that the reflected from the object laser beam coming to a certain point of the primary passes through this point twice, first propagating from the object and second after phase conjugation, when it goes in backward direction. As a result the distortions introduced by the primal)' mirror are canceled. To create the image of the object not at the object itself, as it should be due to phase conjugation, but at some plane located within the telescope, the additional quadratic phase correction can be introduced into the beam with the use of polarization technique when it goes back from the phase conjugate mirror (so called "by - pass concept") 2 The difference in angles of incidence of the beams at the direct and backward passes is one of the most important factors limiting a degree of phase -conjugation correction of aberrations; especially at large f - numbers. However, the degree of primary aberrations reduction due to phase conjugation can be very high in such systems and amounts to tens or hundreds.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.