One of the main problems in tasks of laser beam propagation though Earth’s atmosphere is decrease the efficiency of the optic-electronic systems operation due to atmospheric turbulence influence that leads to laser beam’s wavefront distortions. Use of fast adaptive optical system are suggested to solve this problem. It allows to compensate the wavefront distortions, which upper bound of the spectrum is up to 150 Hz, in real time. Owing to the fact that adaptive optical system is discrete (it’s defined by digital camera included in the system), the sampling rate shall be at least 1500 Hz (frames per second).
The results of experiments carried out on the installation of a fast adaptive optical system with a bandwidth of 1500 Hz are presented. Graphs of the spectral power and normalized energy of Shack-Hartmann wavefront sensor focal spot fluctuations are presented. Theoretical calculations and experimental data are compared. It is shown that in order to achieve a satisfactory correction of distortions caused by turbulence, the system operation frequency should be an order of magnitude higher than the maximum frequency of turbulent distortions.
Increasing of the focusing efficiency of partially coherent laser radiation propagated through a scattering medium was investigated. To improve focusing of scattered laser beam, we applied bimorph deformable mirror with 48 control electrodes and LCOS-SLM with 1920×1080 pixels resolution and compared their efficiencies. We used 5 mm thick glass cuvette filled with the suspension of 1 um polystyrene microspheres, diluted in distilled water. The concentration of scatterers were varied from 105 to 106 mm-3 . According to principle of similarity a medium with such parameters can be considered as an equivalent to the middle-density fog layer with the length ranging from 300 meters up to 5 kilometers. Numerical and experimental investigation of the focusing improvement showed that it is possible to increase the peak intensity of the focal spot up to 60%.
The results of numerical simulations and experiments on the correction of turbulent distortions of a laser beam are presented. The experiments were carried out using an adaptive optical system with a bandwidth of 2000 Hz. It was shown that for effective correction the bandwidth of the adaptive optical system should be an order of magnitude larger than the bandwidth of turbulent distortions.
An adaptive optical system that implements a phase conjugation algorithm designed to compensate for the effect of atmospheric turbulence the propagating laser beam is presented. The system allows compensating for the influence of atmospheric disturbances up to 200 Hz (in terms of sine). To achieve the compensation effect system operates at a frequency of 2000 Hz (in terms of fps - frames per second). Such high performance can be achieved only when using FPGA as the master control element of the system. The results of correction of disturbances obtained by using a heat fan, simulating the turbulence to frequencies of 200 Hz, are presented.
Bimorph deformable mirror with 63 electrodes on 20 mm aperture is discussed. Methods of dividing all round electrode into sectors with a square of 2-4 mm2 are described. Results of flat-top beam formation by means of 50 mm bimorph deformable mirror with 48 electrodes and 20 mm miniature bimorph mirror with 27 electrodes are presented.
We present a device using Shack-Hartmann wavefront sensor for measuring concave optical parts. A technique based on the device makes it easy to measure the main parameters of the aspherical equation of concave aspherical mirrors, radius of closest sphere Rv and eccentricity ε. The described method allows you to reconstruct the shape of the controlled surface in the form of an equation specified during its manufacture.
Laser beam shaping technology nowadays requires as small diameter of the adaptive optics as possible. In our lab we usually control for laser radiation by means of bimorph deformable mirrors with a typical size of more than 50 mm. To fit the most of industrial and scientific applications the aperture of the corrector should be reduced because the use of extra optics instead makes the whole optical scheme more complicated and introduces extra distortions. But in a bid to reduce the size of the mirror we should care of the response of the mirror electrodes which obviously should not decrease drastically. Here we present 20 mm bimorph mirror with high density of electrodes which is manufactured using laser engraving technology to divide the electrode on the piezoceramic disc into a large number of the controlled sectors. The ability of laser beam formation by means of this mirror is discussed, the results are compared with the ones obtained using 50 mm bimorph deformable mirror.
In tasks related to free-space communications, a significant role has a turbulent atmosphere which influences lead to a decrease in the efficiency of systems. Since the characteristic turbulence spectrum rarely exceeds 100 Hz for typical paths, it is proposed to use a discrete adaptive optical system with a frequency of 1500 frames per second to reduce the influence of the atmosphere. The structure of the system based on the use of FPGA as a computing device as well as the main results associated with the correction of both static and dynamic components of aberrations are presented.
The article discusses the use of stacked-actuator adaptive mirrors to improve the focusing of laser radiation. The criterion of focusing efficiency is the fraction of the energy of the laser radiation passing through the pinhole located in the focal plane of the focusing lens.
In this work, we investigate the efficiency of the use of the bimorph deformable mirror to focusing laser beam in the pinhole. Pinholes of different diameters are used as an instrument for focusing verification. Different algorithms are discussed and analyzed for the investigation of the process of the beam focusing. It is shown that tip-tilt correction is an essential condition for increasing the focusing efficiency.
Bimorph deformable mirror with the clear aperture of 50 mm and 48 control electrodes and spatial light modulator with resolution of 1920x1080 pixels were used to increase the efficiency of focusing of partially coherent laser radiation, propagated through the 5 mm layer of the scattering suspension of 1 um polystyrene microspheres, diluted in distilled water, with the concentration values ranging from 105 to 106 mm-3. Medium with such parameters can be considered as an equivalent to the mid-dense fog layer with the length ranging from 300–500 meters up to 5 kilometers. Shack- Hartmann sensor was used to measure the distortions of averaged wavefront of laser beam, and CCD camera was used to estimate the intensity distribution of the focal spot in the far-field. Numerical and experimental investigation of the focusing improvement showed that it is possible to increase the peak intensity of the focal spot up to 45–60 %.
This article discusses the use of bimorph adaptive mirrors to improve the focusing of laser radiation. The criterion of
focusing efficiency is the fraction of the energy of the laser radiation passing through the pinhole located in the focal
plane of the focusing lens.
We present our latest research results on intensity distribution transformation from Gaussian to a flattop and doughnut. The theoretical calculations and experimental results of the efficiency of different types of deformable mirrors are given. During the experiments the wavefront was measured with Shack-Hartmann sensor and then modified with bimorph deformable mirror to reach the desired intensity distribution in the far-field. Then the bimorph mirror was substituted with the stacked-actuators deformable mirror to confirm the simulations.
A high-quality flat wave front is usually used to calibrate the Shach-Hartmann wave-front sensors. The article discusses the possibility of calibrating sensors with spherical wave fronts. Special attention is paid to the consideration of calibration in standard laboratory conditions. The mathematical apparatus and the scheme of the experiment are considered.
The ability to focus laser beam with wavelength 0.65 um through the multiply scattering suspension of polystyrene microspheres, diluted in distilled water, was investigated. Experimental setup, contained the Shack-Hartmann sensor for measurements of the local slopes of the Poynting vector, the CCD camera for estimation of the far-field focal spot’s intensity and the bimorph mirror with 48 electrodes was built. Numerical and experimental investigations of focusing efficiency was carried out also.
Laser beam focusing (λ = 0.65 μm) through the scattering suspension of polystyrene microspheres in distilled water was investigated. Shack-Hartmann sensor was used to measure the local slopes of the Poynting vector, the CCD camera was used to measure the far-field focal spot’s intensity. Numerical and experimental investigations of focusing efficiency of the two bimorph deformable mirrors with 14 and 48 control channels were performed.
The latest results on intensity distribution transformation from Gaussian to a flattop and doughnut are presented in the paper. The wavefront was modified with bimorph deformable mirror to reach the desired intensity distribution in the farfield. LC phase modulator was also considered as an alternative device for laser beam shaping. The theoretical calculations and experimental results of the efficiency of different types of wavefront correctors are given.
The process of remapping the intensity profile of a laser beam is presented. Bimorph deformable mirror was used to change the beam phase; the control signals for the mirror were calculated in accordance with both phase analysis and far-field intensity distribution measurements.
In this paper we consider two approaches widely used in testing of spherical optical surfaces: Fizeau interferometer and Shack-Hartmann wavefront sensor. Fizeau interferometer that is widely used in optical testing can be transformed to a device using Shack-Hartmann wavefront sensor, the alternative technique to check spherical optical components. We call this device Hartmannometer, and compare its features to those of Fizeau interferometer.
We investigated the ability to focus laser beam (λ = 0.65 nm), propagated through the scattering suspension of polystyrene microspheres in distilled water, by means of two bimorph mirrors. Shack-Hartmann sensor was used to measure the local slopes of the Poynting vector, and the CCD camera was used to measure the intensity of the focal spot in the far-field. Correction efficiency of the two bimorph deformable mirrors — with 14 and 31 control channels — were compared. Numerical and experimental investigation of the focusing improvement of the laser beam propagated through the scattering medium was performed.
The transformation of an intensity distribution from Gaussian to a flattop, doughnut, etc. still is a very interesting and important task. And the necessary result could be obtained with the use of adaptive optics that changes the phase of the beam and modifies the shape of the focal spot in the far-field zone. In this paper, we present the flattop and doughnut beam formation result with the use of a bimorph and stacked-actuator deformable mirrors as well as LC phase modulator. The experimental results are also given.
Distortions of the scattered laser beam (λ=0.65μm) were numerically estimated by means of Shack-Hartmann technique
and experimentally measured. The ability to focus laser beam, passed through the scattering suspension of polystyrene
microspheres in distilled water, using bimorph deformable mirror was investigated both numerically and experimentally.
Shack-Hartmann technique was used to measure the local slopes of the Poynting vector, and CCD camera was used to
analyze the intensity distribution of the focal spot in the far-field. Bimorph deformable mirror with 14 electrodes was
utilized in order to increase the focusing efficiency of the laser beam. The voltages to be applied to the mirror electrodes
were calculated using three techniques: LSQ (least squares) fit-error minimization by Shack-Hartmann sensor, Hillclimbing
optimization by Shack-Hartmann sensor and Hill-climbing optimization by the far-field CCD camera.
Laser beam propagation through the scattering suspension of polystyrene microspheres in distilled water was studied. The distorted laser beam was analyzed by both Shack-Hartmann sensor and CCD camera. The measured local slopes of the Poynting vector were compensated for by means of bimorph deformable mirror with 14 electrodes in order to increase the intensity of the focal spot in the far-field. Three different techniques for laser beam focusing were implemented and compared: LSQ fit-error minimization by Shack-Hartmann sensor, Hill-climbing optimization by Shack-Hartmann sensor and Hill-climbing optimization by far-field CCD camera.
We investigate the ability to focus the laser beam (λ=0.65μm) propagated through the scattering suspension of polystyrene microspheres in distilled water by means of bimorph deformable mirror. Shack-Hartmann sensor was used to measure the local slopes of the Poynting vector, while the CCD camera was used to measure the intensity of the focal spot in the farfield. Bimorph deformable mirror with 14 electrodes was applied in order to increase the intensity of the focal spot in the far-field. We investigated the efficiency of the laser beam focusing improvement by means of three techniques: LSQ fiterror minimization by Shack-Hartmann sensor, Hill-climbing optimization by Shack-Hartmann sensor and Hill-climbing optimization by far-field CCD camera.
In this paper we consider two approaches widely used in testing of wide aperture optics: Fizeau interferometer and Shack-Hartmann wavefront sensor. Fizeau interferometer that is common instrument in optical testing can be transformed to a device using Shack-Hartmann wavefront sensor, the alternative technique to check wide aperture optical components. We call this device Hartmannometer, and compare its features to those of Fizeau interferometer.
In this paper we consider two approaches widely used in optical testing: Shack-Hartmann wavefront sensor and Fizeau
interferometer technique. Fizeau interferometer that is widely used in optical testing can be easily transformed to a device
using Shack-Hartmann wavefront sensor, the alternative technique to check optical components. We call this device
Hartmannometer, and compare its features to those of Fizeau interferometer.
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