Using a fast-acting Shack-Hartmann wavefront sensor (WFS) under the conditions of artificially created pavilion turbulence, the possibility of registering and recording the phase front of laser radiation with a high temporal resolution has been experimentally demonstrated. A FPGA has been used as a control element of the WFS that provides an operation frequency of the WFS and recording information about the wavefronts of 4 kHz. Analysis of the reconstructed dynamics of the wavefront of the laser radiation makes it possible to determine in detail various spatiotemporal phase characteristics and to identify non-Kolmogorov features of turbulent distortions.
The numerical study of the efficiency of correction of sinusoidal phase distortions in the adaptive optical system with a finite response time (finite operation speed) has been performed. It has been shown that the operation of the adaptive optical system does not affect the beam quality at the ratio of the adaptive optical system bandwidth to the frequency of sinusoidal distortions νAOS / νturb < 1, laser beam is not corrected. The exceed of divergence over the initial value is observed as the result of correction at the increasing of νAOS / νturb from 1 to 6. The increasing of divergence has replaced by its monotonous decline at νAOS / νturb = 2.5. The decrease in the laser beam divergence relative to the initial value has been observed at νAOS / νturb > 6. The average Strehl ratio upon correction reaches 0.65, and the divergence of the laser radiation exceeds the diffraction limit by a factor of 2 at νAOS / νturb =100. Calculations show that phase distortions with the temporal spectrum in the form of a frequency band with a characteristic frequency νturb require a lower bandwidth νAOS for correction than single-frequency phase distortions with the same νturb.
The results of numerical studies of the possibility and efficiency of intra-cavity phase correction of Cr:CdSe laser radiation with the moving active elements using an adaptive optical system without a wavefront sensor are presented. The beam quality of the Cr:CdSe laser directly depends on the speed of movement of the active element due to the influence of thermal effects. The peak radiation power has determined by the efficiency of the resonator and the cooling system of the active element. It has been shown that the using of intra-cavity adaptive correction in the Cr:CdSe laser can significantly reduce the influence of thermal effects and expand the range of laser operation in single-mode regime.
The results of imaging system resolution enhancement of the astronomical objects by using a Rayleigh laser guide star (LGS) have been presented. Correction of the distortions of stellar optical image has been performed by the adaptive optical system. The numerical simulation of registration of radiation from the Rayleigh LGS by a Shack-Hartmann wavefront sensor has been carried out. It has been shown that accurate calculation and subtraction of magnitude of the defocus and tip-tilts allows mitigating the reconstruction error concerned with the finite distance to LGS and the angular position of the telescope. It has been demonstrated in the experiment that angular size of the natural star Scheat decreases by 3 times at the use of Rayleigh LGS at range of 5 km.
Numerical studies of the phase correction of a laser beam passed the turbulent atmosphere by an adaptive optical system with a Shack-Hartmann wavefront sensor have been performed. Criteria for the correction efficiency have been obtained under different the spatial resolution of an adaptive mirror and the Shack-Hartmann wavefront sensor for various values of the Fried parameter.
Numerical investigations of multi-channel laser radiation focusing efficiency through the optically inhomogeneous medium at the phasing on the system output and in the target-in-the-loop technique based on stochastic parallel gradient (SPG) algorithm have been performed. The efficiency of focusing according to the ratio of Fried’s parameter to subaperture size has been investigated.
The results of experiments conducted on a laboratory setup of a fast adaptive optical system based on the use of FPGA as the main control element and a bimorph mirror as a wavefront corrector are presented. The adaptive system bandwidth ranged from a dozen Hertz to 2,000 Hertz. For independent control of the quality of correction the intensity distribution in the far field was recorded. It is shown that for a good correction of the wavefront the system bandwidth should be an order of magnitude higher than the upper boundary of the spectrum of wavefront distortions caused by turbulence. A comparison of the model and experimental data is also presented.
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.
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.
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