Adaptive Optics

The level of modern optical technologies allows creation of optical devices with characteristics approaching the theoretical limits. The practical achievement of these characteristics encounters hardly eliminated physical factors - turbulent fluctuations of refractive index of an atmosphere, thermal deformations of optical elements etc.

The hope to compensate these effects in real time caused the birth of new branch in optics - adaptive optics. Its methods assume the correction of a wave front of light radiation by any adaptive element, such as deformable mirror or spatial phase modulator. ASC "Femto" specializes on design, manufacturing and testing of adaptive optical systems of various purposes, including informative or laser multichannel adaptive optical systems with wavefront sensors in visible or infrared ranges of waves.

Our synthesized algorithm of adaptive system operation is realized in the optical processor which is carrying out full parallel signal processing in channels of control of deformable mirror drives. The main difference from known Hartman schemes lies in the absence of complex signal recalculations from the photosensor response into signals of deformable mirror control. Due to this approach, escalating system with any reasonable number of control channels (103 and more) is possible to make, its size and system power consumption being reduced to minimum.

Informative adaptive systems are intended for correction of distortions of wave front of a turbulent atmosphere and residual aberrations of optics with the purpose of reception of the high-quality image of the remote object or with the purpose of maintenance of optical communication at large distances.

Here are a few directions of application of informative adaptive optics:

  astronomical systems of high angular resolution
  systems of optical communication
  imaging systems at ground ranges up to 4-10km

Today, the first and the second directions are clear enough for broad body of experts, and in ASC "Femto" the adaptive systems to solve these problems are already created and successfully tested. The third direction requires comments. An attempt to use of adaptive optics at observation in a ground layer of an atmosphere gives rise to a question of the size of isoplanatic area of atmosphere. It is accepted to consider as isoplanatic area of atmosphere the size of domain in space of objects for which distortions of wave front appear practically identical at all points in this domain. This size limits the corrected field of vision that may be received with application of usual adaptive optics. In visible range of wavelengths the size of isoplanatic area may be about several millimeters and less at the distances 4-10km. The essential increase of a field of vision is possible with use of an infrared range of wavelengths (the size of isoplanatic area quickly grows with increase of wavelength). In near future we hope to obtain the first experimental results in use of infrared range adaptive system.

Laser adaptive systems are intended for correction of wave front distortions of sufficiently powerful technological lasers. In ASC "Femto", various systems of this type are created both with application of our original wave front sensor and on the base of a well-known technique of multifrequency aperture sounding. Distinctive feature of these systems are the rather large working aperture of a deformable mirror (100mm-200mm) and, probably, the compulsory water-cooling or air-cooling of the deformable mirror.

To overcome the restriction connected with anisoplanatizm of a turbulent atmosphere is possible with an application of the so-called multiconjugative adaptive systems. The basic idea consists in the necessity to compensate an atmospheric distortions not with one deformable mirror, but with the several mirrors conjugating with different layers of atmosphere. The main problem is to create the effective sensor carrying out "multilayer" measurement of distortions. The scheme of such sensor is developed in ASC "Femto". The computer model confirming its efficiency is already compiled. In case of the customer order, manufacturing and delivery of an experimental sample of the multiconjugative adaptive system is possible.

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