The main postulates of adaptive correction of distortions of the wave front in large-size optical systems

• Main Author: V. V. Sychev
• Format: Article
• Language: Russian
• Published: MGTU im. N.È. Baumana 2014-01-01
• Series: Nauka i Obrazovanie
• Subjects: laser radiation; adaptive correction; the wave front of emission; phase corrector
• Online Access: http://technomag.edu.ru/jour/article/view/556

<p>In the development of optical telescopes, striving to increase the penetrating power of a telescope has been always the main trend. A real way to solve this problem is to raise the quality of the image (reduction of the image angular size under real conditions of distorting factor) and increase a diameter of the main mirror. This is counteracted by the various distorting factors or interference occurring in realtime use of telescopes, as well as by complicated manufacturing processes of large mirrors.</p><p>It is shown that the most effective method to deal with the influence of distorting factors on the image quality in the telescope is the minimization (through selecting the place to mount a telescope and choosing the rational optical scheme, creating materials and new technologies, improving a design, unloading the mirrors, mounting choice, etc.), and then the adaptive compensation of remaining distortions.</p><p>It should be noted that a domestic concept to design large-sized telescopes allows us to use, in our opinion, the most efficient ways to do this. It means to abandon the creation of "an absolutely rigid and well-ordered" design, providing the passively aligned state telescope optics under operating conditions. The design must just have such a level of residual deformations that their effect can be efficiently compensated by the adaptive system using the segmented elements of the primary mirror and the secondary mirror as a corrector.</p><p>It has been found that in the transmission optical systems to deliver laser power to a remote object, it is necessary not only to overcome the distorting effect of factors inherent in optical information systems, but, additionally, find a way to overcome a number of new difficulties. The main ones have been identified to be as follows:</p><p>• the influence of laser radiation on the structure components and the propagation medium and, as a consequence, the opposite effect of the structure components and the propagation medium on the transmitted radiation WF;</p><p>•  the lack of a reference source at the wavelength of trasnmitted laser radiation, which is required to implement methods for adaptive correction of the distorted WF;</p><p>•  the unique to laser systems additional distorting factors available in transmission systems.</p><p>These distorting factors include:</p><p>• length of the optical path due to need in spatial diversity of high power laser source with a large number of matching optical elements;</p><p>• thermal self-action of power laser radiation in the transport path of the radiation before its entry into forming optical system;</p><p>• instability of spatio-temporal characteristics of the laser radiation source itself to take a turn for the worse conditions of radiation transmission both inside the optical path, and in the free atmosphere;</p><p>• thermal irregularities and thermal deformation.</p><p>It is shown that the adaptive systems differ from the active optics in that radiation wave front distortion is corrected in real time per totality of distorting factors (not only on the effect of the atmosphere) with the speed ten times exceeding the effect of distortion itself. Here, the correction quality is estimated by criterion of the primary image quality.</p><p>In this case, the correction continuously takes into account data about optical system parameters such as current space, temperature, time, and adjusting, thereby supporting the high quality of images under the action of distorting factors.</p><p>The paper formulates and proposes the basic postulates of adaptive correction.</p><p>Postulates are a set of statements and assertions, allowing us to implement effective means of adaptive correction of distortions.</p><p>The paper also shows the real capabilities the methods and means of adaptive optics offer in case of efficient use of laser radiation power and what ways are possible to solve these tasks. First of all, these are:</p><p>- forming a system of assumptions and minimization of distortions in the optical path, which includes a laser cavity, a transport channel of powerful laser radiation with deflecting mirrors and a forming telescope with a segmented primary mirror;</p><p>- formation of the performance criteria of adaptive optical systems;</p><p>- multiplanimetric system of adaptive correction of distortions.</p><p>The paper discusses test results of the transportation of powerful laser radiation on a horizontal track and shows an external view of forming optical system of comprehensive test stand.</p><p>It is conclusively proven that using the proposed postulates when developing or modernizing the optical systems provides the lowest level of residual distortions and the operating efficiency of adaptive optical means.</p><p>The proposed postulates for adaptive correction of radiation WF and positive experience of their use in full-scale optical complexes significantly reduce time and cost in developing the effective means to observe the distant objects, as well as the means to generate and supply power to various space objects for its multiple use such as power supply, telecommunications, fighting with space debris, providing security asteroid etc.</p><p>It can be concluded that the state of the domestic optical science and its potential in the field of adaptive means to form and transport high-power laser radiation, as well as the results of theoretical and experimental studies, inspire the reasonable hope for the high-performance large-sized multipurpose optoelectronic devices to be available in the future.</p>