Adaptive System for Vortex Laser Beams
Adaptive Optical System for Phase Correction of Laser Beams with Wave Front Vortices
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
8 Project completed
Senior Project Manager
Malakhov Yu I
VNIIEF, Russia, N. Novgorod reg., Sarov
- Limited society Adpot, Russia, Moscow\nInstitute of the Problems of Laser and Information Technologies, Russia, Moscow reg., Shatura
- THALES, France, Orsay\nAir Force Research Laboratory(AFMC)/DELG, USA, NM, Kirtland\nDepartment of the Navy / Naval Research Laboratory / Remote Sensing Division, USA, NM, Kirtland\nUniversity of Electro-Communications / Institute for Laser Science, Japan, Tokyo\nQinetiQ, UK, Malvern\n[Individual specialist]
Project summaryThe present Project is devoted to the development and creation of effective adaptive optical systems for correction of large phase distortions of the laser beam wave fronts. One of the most urgent problems in this area is to achieve effective functioning of adaptive optical systems in conditions of strong turbulence when a coherent light field becomes a speckle field (problem of strong turbulence). This field is characterized by the presence of isolated points, in which intensity goes to zero and the phase turns out to be undefined. Circulation of the phase gradient along the contour surrounding such a point turns out to be nonzero, which means the presence of a screw phase dislocation.
Of great interest are also the tasks of adaptive corrections of aberration upon ophthalmologic investigation of the eye-ground. Such tasks become of primary importance in connection with the possibility of modern medicine to forecast both the existing and incipient pathologies of a human organism and correspondingly offer the methods of treating them basing on the eye-ground picture. However, for obtaining a high-quality image of the retina it is necessary to compensate various aberrations caused by both a nonideal form of the eye lens and optical nonuniformity of the gelatinous medium of the eye globe and nonuniform thickness of the eye tear. This leads to considerable distortions in the picture of the eye-ground dependent on a concrete patient. The analysis of the interference patterns of eye aberrations shows the possibility for appearance of the wave front phase dislocations.
The principle of operation of phase reconstructors of present-day adaptive optical systems is based on the assumption that the phase distribution across the beam is a smooth continuous function of spatial coordinates. In the presence of phase dislocations in the light field the wave front reconstruction on the basis of these principles becomes impossible. Recording of the phase dislocation position itself is a nontrivial experimental problem. Yet a more complex problem is the development of effective algorithms of phase reconstruction and creation on their basis of effectively functioning correctors of wave fronts containing singularities of phases.
The whole Project is a combination of separate theoretical and experimental tasks solved in certain stages independently. The first experimental task is to generate a laser beam containing phase singularities with controlled parameters. Further phase distortions of the probe beam are measured either by a wave front sensor of the Hartmann type or by a sensor of the combined type (a sensor of the wave front curvature). The data obtained by using it are the initial data for determining the position and parameters of phase singularities and subsequent reconstruction of the phase distribution. Experimental measurements must be made with sufficient (for subsequent phase reconstruction) spatial resolution.
The next task is to develop methods for phase reconstruction. It is assumed that the phase reconstruction algorithms will be based on the presentation of the vector field of slopes in a form of the sum of the potential (vortex-free) and solenoidal components. Such representation allows us using strict integral relations to calculate the “density of phase sources” and the “density of phase vortices”. Preliminary estimations show that the suggested approaches to the solution of the visualization problem of local phase singularities (phase vortices) and to the development of phase reconstruction algorithms turn out to be stable to the effect of random errors made during measurements. The task of development of sufficiently fast-acting and stable to noises algorithms is one of the main tasks of the proposed Project. The first calculations show that compensation of optical beam phase distortions alone in a number of cases is sufficient for achieving the acceptable level of efficiency of the adaptive optical system.
In the course of works on Project it is necessary to choose or develop a method for correction (compensation) of the wave front and create a system of correction (compensation) itself. Experimental investigations of the efficiency of such an adaptive system in conditions of a steady state mode of controlled phase distortions are to be conducted in the final phase of the Project.
It is supposed that in the course of works on this Project the following results will be achieved:
– Experimental methods will be developed for recording the location and parameters of phase dislocations of the laser beam wave front;
– Methods and algorithms will be developed for the phase reconstruction in the presence of wave front singularities;
– Numerical model of a flexible mirror (with continuous reflecting surface) as well as the numerical model of a compound mirror will be developed, which then will be used for creation of the corrector of singular phase fronts;
– Programs will be developed for control of the corrector;
– Experimental investigations will be conducted on the correction of singular phase distortions. Efficiencies of operation will be determined for the created model adaptive optical systems in the range of frequencies up to 70 Hz as well of the developed programs for the control of the corrector of wave fronts containing phase dislocations.
For a number of years the scientists and specialists involved in the Project have performed investigations connected with laser radiation propagation at its linear and nonlinear interaction with matter, wave front conversion, dislocations properties, development of methods for phase distribution reconstruction in the wave front in the presence of dislocations, and with creation of systems of adaptive optics.
Within the scope of the present Project it is supposed to use the knowledge of Project participants from the Russian Federal Nuclear Center – VNIIEF earlier engaged in investigations connected with the development of nuclear weapon and having rich experience in experimental investigations and numerical modeling. Their work in the scope of this Project jointly with Institute on Laser and Information Technologies (ILIT, Shatura, Moscow Region), Lomonosov Moscow State University, Institute of Atmospheric Optics (IAO, Tomsk) will proceed with participation of skilled scientists and consultants, the pioneers in the field of adaptive and singular optics.
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