The results of full-scale experiments in the atmosphere with various turbulence state meters are considered. In measurements on horizontal open atmospheric paths of various lengths, three optical meters and an acoustic weather station were used. Based on the test results of the meters, a high correlation of turbulence measurements made by optical differential meters DIT-2 and DIT-M as well as the AMK-03 ultrasonic acoustic weather station was shown. Conclusions are drawn about the accuracy and applicability of the meters used to assess the level of turbulence along the atmospheric paths.
This development is carried out in the interests of creating a remote optical meter operating on the optical signal of a weak extra-atmospheric source - such as a star. It will allow obtaining data on turbulence for inclined paths at different heights above the underlying surface, and will also make it possible to detect the presence of turbulent layers in the atmosphere, including the presence of non-Kolmogorov turbulence in the atmosphere. For this purpose, it is planned to create two single-channel mock-ups of image jitter meters operating on signals from two different optical sources in a scheme with intersecting lines of sight. Atmospheric experiments have been carried out to compare the results of measurements of atmospheric turbulence by various methods.
The random inhomogeneities of the refractive index due to turbulent motion in the atmosphere cause a significant decrease in the theoretical resolution of an optical telescope, cause such well-known effects as scintillation, jitter, and degradation of the optical images. Adaptive optics (AO) systems with a laser guide star (LGS) are designed to eliminate the negative effects. The main limitation of LGS is the problem of measuring the global tilt. We offer the approach to using the LGS signal. The approach, where initially the LGS is considered as a point source of spherical wave with a random center is considered. The results of analytical and numerical calculations are reported. The estimation of sodium column density and height peak of sodium mesospheric layer above large Russian Observatories are presented also.
The temporal error is the main problem for adaptive optical systems operating in the atmosphere. One way to solve this problem is to optimize the adaptive optics system by predictive control algorithms. In study the adaptive optical system installed on the small-aperture telescope with the predictive algorithm are developed. The predictive algorithm uses measurement of center gravity of light intensity at subapertures of the Shack-Hartmann wavefront sensor has been developed. In results it not depends on the type and design of the adaptive mirror. For implementation the Shack- Hartmann wavefront sensor measuring phase distortion, atmospheric turbulence, and transverse wind velocity are created. The design of the wavefront sensor allows replacement of the microlens array with different sizes, focal lengths and operated in wide range of phase aberrations. As a result, the adaptive optics system measure the level of optical atmospheric turbulence for replace the microlens array and it to operated in different turbulent atmospheric conditions.
The temporal error of the adaptive optical system leads to a significant degradations in the characteristics of the system operating in the atmosphere. One of the methods for solving this problem is the use of prediction algorithms based on the analysis of the evolution of phase fluctuations. In the paper the wavefront sensor as the key element of atmospheric adaptive optical system with predictions algorithms is considered. The results of the development and testing of the Shack-Hartmann wavefront sensor providing measurements of phase fluctuations, determination of the Fried parameter and wind speed using original design solutions and software are presented. The practical and theoretical aspects of using the Shack-Harmann wavefront sensor are discussed. For it dynamic range, sensitivity and accuracy of the sensor are estimated. The influences of parameters of microlens array on range of measurements of the Shack-Harmann wavefront sensor are studied. The tests of the S-H WFS were carry out with acoustic measurements of wind speed and the structural constant of the refractive index of the atmosphere, as well as in adaptive optics system in laboratory test bench.
We describes the status of AO test bench, which is developing at the Adaptive optics Lab, V.E. Zuev Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Sciences (IAO SB RAS), Tomsk, Russia to simulate predictive algorithms of wavefront adaptive correction. The description of the optical and mechanical design, components AO bench, and the working principle and first experimental results are presented. The current AO test bench consists of laser source, two deformable mirrors with 59 actuators and 56 mm diameter (Visionica Ltd., Russia), two tip/tilt mirrors (IAO SB RAS, Russia), Shack-Hartmann Wavefront Sensor (WFS), which we specially designed, and a science camera for the evaluation of the performance. The user derived aberrations are introduced using a one deformable mirror and corrected by another deformable mirror. The tip/tilt mirrors are used for predictive control of the low-order wavefront aberrations related such as vibrations.
The results of experimental studies of the effect of atmospheric turbulence in the adaptive optical image correction system at the Baikal Large Solar Vacuum Telescope (LSVT) are presented. To eliminate the jitter and stabilize the image on the receiver, the appropriate hardware and software system that corrects the tilts of incoming wave front with frequencies up to 1 kHz has been developed in the Laboratory of the Coherent Adaptive Optics (LCAO). To obtain digital images of high resolution, the tip-tilt adaptive system is combined with a post-detection computer processing of frames using fast 2D parallel real time algorithms. Experimental data confirm the high efficiency of the dual adaptive system for stabilizing and forming images on the LSVT.
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