Sergei A. Dimakov

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.

Powerful Nd:YAG laser of two active elements with improved divergence of output beam

An unstable resonator for a laser based on two Nd:YAG active elements with induced thermal lenses is proposed and investigated. The output beam divergence greater by factor 2 than the diffraction limit is achieved. The radiation power of the laser with the resonator proposed has been obtained 20% below but with the 30 times greater on-axis intensity as compared to the ordinarily used resonator in a commercial laser of a similar type.

Phase conjugation in a high-power E-beam-sustained CO2 laser

The experimental demonstration of phase conjugation technique as applied to aberration correction in a high-power gas-flow CO2 laser is reported. A four-wave mixing in 34SF6 was used to obtain high efficient phase conjugation of repetition rate electron- beam-sustained CO2 laser radiation. For the first time, the nearly diffraction-limited performance of the double-pass CO2 amplifier with the phase-conjugate mirror for the output energy of about 1.2 KJ and average power of 40 KW is demonstrated.

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).

Feasible configurations of a repetitively pulsed TEA CO2 laser with small angular divergence and 1- kJ pulse energy

The results are presented of expert evaluations aimed at developing the optimal concept of creation of a compact TEA CO2 laser with a self-sustained discharge capable of generating the repetitive bursts of ten radiation pulses with 1 kJ-energy in each and the pulse repetition rate of 30 Hz. Particular emphasis is placed on the problems of achieving as small angular divergence and beam wandering as possible.

Compensation for distortions of a telescope's primary mirror by means of a volume dynamic hologram

We describe a number of experiments devoted to compensation for aberrations in the primary mirror of a telescope using a volume dynamic holography technique, where the writing and reading of the hologram are carried out independently. Three sets of experiments demonstrating holographic aberration correction have been performed. In all cases transmitting holograms were formed in photorefractive crystals such as BSO and SBN. In experiments with a small diameter primary mirror the image is formed by a multicolor point-like object. The system includes a unit which compensates for the hologram dispersion. The aberration correction of a six- segmented primary mirror of 150 mm in diameter is demonstrated in conditions where there is a pronounced difference in the wavelengths of the recording beams and that of the source observed (Δλ=0.12 μm). The experiments on observation an extended object of continuous spectrum (Δλ=0.35 μm) with a single primary mirror of 150 diameter have been also made. All these experiments indicate an efficient compensation of distortions of the primary mirror by the hologram.

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.

CO2 lasers and phase conjugation

Abstract not available.