Boris V. Kislitsyn

Features of application of elastic membrane primaries in observing telescopes with nonlinear optical correction of images

Some last ten years the problem of compensation for dynamic distortions of primary mirrors in low-weight large-size imaging telescopes by methods of dynamic holography is actively being investigated. Today the performance of such systems has been experimentally proved. Thus, the idea to use in such a telescopic system a low-weight-film primary mirror, which can, in principle, be of large diameter in an unfolded mode, is very attractive one. In this paper the problems are considered related to integration of a thin- film primary mirror in a telescope with a non-linear corrector for an object image. Namely, there will be discussed the architecture of the telescope with the thin- film primary, optical quality of the mirror, requirements on the non-linear corrector, the telescopes field of view, and quality of the image of an object.

Factors disturbing a preshaped membrane mirror

Today the peak of the conventional method of telescope design is the space telescope named after Hubble (2,4 m-diameter of the primary mirror). Further increase of the input-aperture diameter of telescopes requires the application of new architectures of their design based on the recent progress in optics and the development of super-light mirrors. The paper is devoted to development of the concept of a new-generation membrane primary mirror for extra-atmospheric imaging telescopes basing on the recent progress in non-linear technique of correction for dynamic distortions.

Thermo-correction of quasi-static optical distortions for EUV lithography

Now optical reducing systems for extreme ultraviolet projection lithography are being actively developed. Optical elements of these systems are required to be of super-high optical quality. For systems operating in the 13-nm wavelength range, their optical distortions should not exceed 1 nm in magnitude. Manufacturing of such elements with super-high optical quality requires large financial injections. In this report, we consider how to use thermal deformation of an optical element exposed to light for improvement of optical quality of the element. It is shown, in particular, that residual quasi-static large-scale (20% of diameter of the element) optical distortions, about 15 nm in magnitude, can be compensated with the proposed technique down to 0.5 nm (i.e. ≈ λ0/20 - λ0/30 for EUV).

Control of membrane mirror profile by electrostatic field

Nowadays, membrane mirrors are being under study. They are interesting from the application standpoint in telescopes with aberration correction (by phase conjugation or real-time holography methods). To give the required spherical or parabolic shape to these mirrors to be employed in the space, the mirror surface is exposed to, for example, gas pressure. For this is the cavity between two membranes, one being transparent (canopy) and the other specular, is filled with the gas. The transparent membrane appears to be undesired in a number of cases since its possible distortions have to be compensated for that a high quality image of the object observed through the telescope to be achieved. However in a number of cases the gas pressure action may be simulated with a proper electrostatic field. In this paper results of electrostatic field effect on the shape of the mylar-film mirror with reflecting coating are presented. Here is also given an analysis of the shape of the membrane mirror exposed to both an electrostatic-field load normal to and a strain load along its surface. It is shown that in the case of the electrostatic load the surface shape can be more close to a parabolic one than that in the uniform pressure case.

Analysis of the elasticity theory equations aiming to clear up main relationships of the parameters in the thin-flexible-mirror task

The state of the thin axial symmetric elastic mirror under deformation tension is considered in approximation of the thin membrane theory. The solution of the equations is presented here describing the mirrors distortions under both the pressure applied across the film and the stretching forces along the film. To study optical quality of the flexible mirrors surface, the calculations were performed of energy angular distribution of the reflected radiation (for incident plane-front beam) in the focal plane of the elastic mirror.

Thermo-correction of quasi-state optical distortions in optical reducing systems for EUV projection lithography

Optical reducing systems for the extreme ultraviolet projection lithography are actively developed in the last few years. Optical elements of these systems are required to be of super-high optical quality. For the systems operatingin the 13-nm wavelength range, their optical distortions should not exceed 1 nm in magnitude. Manufacturing of such elements requires large financial injections. In this report, we consider how to use thermal deformation of an optical element exposed to light for improvement of optical quality of the element. It is shown, in particular, that residual quasi-static large-scale (20% of diameter of the element) optical distortions, about 15nm in magnitude, can be compensated with the proposed technique down to 0.5 nm (i.e.≈λ0/20 - λ0/30 in the EUV).

Electrically controlled preshaped membrane mirror for systems with wavefront correction

The paper is devoted to investigating the ways of development of the lightweight mirrors with imperfect optical quality but still suitable for being used in the telescopes with the primary mirrors aberration correction. The work involves the studies aimed at creation of the lightweight membrane mirrors with satisfactory optical quality and a suitable value of the F-number of around 1. As the first step, we demonstrate the possibility to control parameters of a pre-shaped membrane mirror by means of electrostatic field. It is shown that both the spherical component of the shape of the membrane mirror and its astigmatism can be controlled using the proposed approach.

Coordination of primary mirror parameters with corrector parameters in telescope with real-time correction of aberration

During the last years, a considerable advance has been made in the development both of optical telescopes with the real-time image correction and of the concept of the light-weight telescope primary mirror. In spite of the progress in the design of the phase correctors, their parameters (such as spatial resolution, speed, accuracy of the correction, noise level, transverse dimensions, etc.) still do not completely satisfy the requirements to the distortion correctors for the light-weight mirrors of large diameter. At the same time, the optical nonideality of the light-weight mirror is an adjustable parameter depending, in the main, on the degree of lightening of the mirror weight. Thus, for optimization of the process of the distortion correction in telescopes of this type, parameters of the primary mirror (PM) and corrector should be matched with each other. As the first step towards this optimization, we will discuss, in this presentation, the so-called cross-requirements to the PM and corrector, i.e., the requirements imposed on the corrector from the viewpoint of ease of fabrication of the PM and the requirements of the PM quality from the viewpoint of the best nonlinear-optical correctors available nowadays.

Computer-based telescope with double phase-diversity

The future telescopes indeed for exploring deep space should possess a large-clear-aperture low-weight primary mirror. Optical quality of such a mirror will apparently be non-ideal and, therefore, such a telescope will have to be supplied with a system of image correction. We consider a computer-based telescope comprising its primary mirror (PM) of a non-ideal optical quality, a laser system illuminating the PM to inquire the distortions of the specular surface, secondary optics, CCD matrices, and a computer with a proper software. This telescope allow one, in principle, to obtain images of deep-space objects with a high angular resolution in the time-delayed (rather than real-time) mode because of computer processing of the information. In the paper, we also discuss advantages and disadvantages of the analog (nonlinear optical) and digital (phase-diversity) image correction techniques.

Membrane primary mirror for a telescope with a real-time holography corrector

During some last years an interest has grown in usage of membrane elastic primary mirrors in both beam-projecting and imaging telescopes comprising a nonlinear-optical correction system. Theoretical and experimental studies of these mirrors based on a plane membrane uniform in thickness, at pressure applied along the normal to its surface and tension applied at its edges, have shown that aberrations of such a mirror (with aperture approximately 3 m and relative aperture approximately 1:2) are in the visible wavelength range too large to be compensated with the use of the existent correction systems. In this paper it is proposed for improvement of optical quality of the mirror surface to employ either a plane- membrane mirror variable in thickness or a mirror based on an initial-surface-profile membrane. The presented numerical results of calculation of both the mirror shape and the range of aberration parameters for these mirrors show that aberrations available prove to be lower in magnitude than those of the required level.