Cross-wind profiling based on the scattered wave scintillation in a telescope focus.

The problem of wind profile reconstruction from scintillation of an optical wave scattered off a rough surface in a telescope focus plane is considered. Both the expression for the spatiotemporal correlation function and the algorithm of cross-wind velocity and direction profiles reconstruction based on the spatiotemporal spectrum of intensity of an optical wave scattered by a diffuse target in a turbulent atmosphere are presented. Computer simulations performed under conditions of weak optical turbulence show wind profiles reconstruction by the developed algorithm.

[Results of using the domestic vascular prosthesis "Ekoflon"]. / Rezul'taty ispol'zovaniia otechestvennykh sosudistykh protezov "Ekoflon".

The aim of the work was to study long-term results of application of a vascular transplant from modified polytetrafluoroethylene "Ekoflon". The investigation included 121 reconstructions performed during the last 6 year, 53 prostheses being implanted in the aorto-femoral position, 68--in the femoro-popliteal-tibial position. The long-term results have shown that the transplant "Ekoflon" in the position of the aorto-femoral shunt is not inferior to textile analogues and even has a number of advantages. When it is used below the inguinal fold the results of patency were worse than those with the autovenous one. But when there is no adequate autovein, under conditions of critical ischemia, prosthesis "Ekoflon" might be the material of choice for saving the lower extremity. The dynamic ultrasound duplex scanning and histological investigation of the prosthesis samples have shown an original morphogenesis of its "implantation".

Adaptive phase distortion correction in strong speckle-modulation conditions.

We introduce beam-quality metrics for adaptive wave-front control that permit estimation of the degree of laser beam energy concentration on a remotely located extended object based upon the backscattered wave intensity distribution at the receiver. A 37-control-channel adaptive optics system with phase correction of the output wave capable of operating in the presence of speckle-field-induced strong intensity modulation is presented. System operation is based on optimization of the speckle-field-based metric by the stochastic parallel gradient descent technique. Results demonstrate that adaptive wave-front correction using speckle-field-based beam-quality metrics can significantly improve laser beam concentration on extended objects.

Chaotic free-space laser communication over a turbulent channel.

The dynamics of errors caused by atmospheric turbulence in a self-synchronizing chaos-based communication system that stably transmits information over an approximately 5 km free-space laser link is studied experimentally. Binary information is transmitted using a chaotic sequence of short-term pulses as a carrier. The information signal slightly shifts the chaotic time position of each pulse depending on the information bit. We report the results of an experimental analysis of the atmospheric turbulence in the channel and the impact of turbulence on the bit-error-rate performance of this chaos-based communication system.

[Application of different textile vascular grafts in the aorto-femoral location and ways for their improvement]. / Primenenie razlichnykh tekstil'nykh sosudistykh transplantatov v aortobedrennoi pozitsii i puti ikh sovershenstvovaniia.

A comparative analysis of 220 reconstructions of the aortofemoral segment with the application of vascular prostheses of firms "Sever" and "Vascutek" was made. It was established that in patients with obvious anemia and hemodilution (hematocrit less than 25%, hemoglobin less that 80 g/l) an important condition for less total blood loss was to impart the zero surgical porosity to the graft wall at the preoperative stage. However, the biological impregnation used for these purposes reinforces the inflammatory component in the implantation of the vascular graft. The authors propose to use a more inert polytetrafluoroethylene film to impart the zero surgical porosity to the graft wall.

Adaptive optics with advanced phase-contrast techniques. I. High-resolution wave-front sensing.

High-resolution phase-contrast wave-front sensors based on phase spatial light modulators and micromirror/ liquid-crystal arrays are introduced. Wave-front sensor performance is analyzed for atmospheric-turbulence-induced phase distortions described by the Kolmogorov and the Andrews models. A high-resolution phase-contrast wave-front sensor (nonlinear Zernike filter) based on an optically controlled liquid-crystal phase spatial light modulator is experimentally demonstrated. The results demonstrate high-resolution visualization of dynamically changing phase distortions within the sensor time response of approximately 10 ms.

Adaptive optics with advanced phase-contrast techniques. II. High-resolution wave-front control.

A wave-front control paradigm based on gradient-flow optimization is analyzed. In adaptive systems with gradient-flow dynamics, the output of the wave-front sensor is used to directly control high-resolution wavefront correctors without the need for wave-front phase reconstruction (direct-control systems). Here, adaptive direct-control systems with advanced phase-contrast wave-front sensors are analyzed theoretically, through numerical simulations, and experimentally. Adaptive system performance is studied for atmospheric-turbulence-induced phase distortions in the presence of input field intensity scintillations. The results demonstrate the effectiveness of this approach for high-resolution adaptive optics.

Anisoplanatic imaging through turbulent media: image recovery by local information fusion from a set of short-exposure images.

A wide-field-of-view white-light imaging experiment with artificially generated turbulence layers located between the extended object and the imaging system is described. Relocation of the turbulence sources along the imaging path allowed the creation of controllable anisoplanatic effects. We demonstrate that the recently proposed synthetic imaging technique [J. Opt. Soc. Am. A 16, 1623 (1999)] may result in substantial improvement in image quality for highly anisoplanatic conditions. It is shown that for multisource objects located at different distances the processing of turbulence-degraded short-exposure images may lead to a synthetic image that has an image quality superior to that of the undistorted image obtained in the absence of turbulence (turbulence-induced image quality enhancement).

Microscale Adaptive Optics: Wave-Front Control with a mu-Mirror Array and a VLSI Stochastic Gradient Descent Controller.

The performance of adaptive systems that consist of microscale on-chip elements [microelectromechanical mirror (mu-mirror) arrays and a VLSI stochastic gradient descent microelectronic control system] is analyzed. The mu-mirror arrays with 5 x 5 and 6 x 6 actuators were driven with a control system composed of two mixed-mode VLSI chips implementing model-free beam-quality metric optimization by the stochastic parallel perturbative gradient descent technique. The adaptation rate achieved was near 6000 iterations/s. A secondary (learning) feedback loop was used to control system parameters during the adaptation process, further increasing the adaptation rate.

Synthetic imaging: nonadaptive anisoplanatic image correction in atmospheric turbulence.

We introduce a synthetic-imaging technique that can be applied to correct anisoplanatic images degraded by atmospheric turbulence. This method is based on local image-quality analysis applied to a large set of short-exposure images and can be considered a generalization of the frame-selection technique. Experimental results obtained for atmospheric data demonstrate the efficiency of the synthetic-imaging technique in improving image quality.

Adaptive phase-distortion correction based on parallel gradient-descent optimization.

We describe an adaptive wave-front control technique based on a parallel stochastic perturbation method that can be applied to a general class of adaptive-optical system. The efficiency of this approach is analyzed numerically and experimentally by use of a white-light adaptive-imaging system with an extended source. To create and compensate for static phase distortions, we use 127-element liquid-crystal phase modulators. Results demonstrate that adaptive wave-front correction by a parallel-perturbation technique can significantly improve image quality.

Adaptive imaging system for phase-distorted extended source and multiple-distance objects.

We introduce an incoherent adaptive imaging system based on optimization of an image quality metric measured using a coherent optical system. Experimental results and numerical simulations are presented that demonstrate adaptive correction of phase-distorted extended source images containing objects located at multiple distances.

[Experimental and clinical research on the Russian Vitaflon blood vessel prosthesis]. / Eksperimental'no-klinicheskoe issledovanie otechestvennogo proteza krovenosnykh sosudov "Vitaflon".

The authors have performed an experimental and clinical assessment of a new graft. In 37 mongrel dogs 49 experiments were carried out with the implantation of grafts "Vitaflon" into different parts of the arterial and venous bed. It was shown that the domestic graft from modified polytetraftoroethylene had high biological inertia, good plastic properties, zero surgical porosity, strength and reliable "taking" by the recipient's organism. Following the experimental work the prosthesis "Vitaflon" (30-50 cm long and 8 mm diameter) was implanted in the femoro-popliteal-tibial position to 15 patients suffering from obliterating atherosclerosis of the lower extremity arteries. The period of follow-up observations was about 12 months. Thrombosis took place in two grafts in the early postoperative period. Other shunts were functioning well which was confirmed by the clinical picture and dopplerography.

Spatiotemporal dynamics of self-pumped phase conjugation in a photorefractive crystal: multipattern storage using incremental recording.

We investigate the spatiotemporal dynamics of self-pumped phase conjugation for superimposed incrementally recorded images. Experimental evidence of time delay in the appearance of phase-conjugation patterns was observed during both the recording and the readout phases.