Vladimir Y. Baranov

Three-dimensional microwave tomography: initial experimental imaging of animals

The purpose of this study was to construct a microwave tomographic system capable of conducting experiments with whole scale biological objects and to demonstrate the feasibility of microwave tomography for imaging such objects using a canine model. Experiments were conducted using a three-dimensional (3-D) microwave tomographic system with working chamber dimensions of 120 cm in diameter and 135 cm in height. The operating frequency was 0.9 GHz. The object under study was located in the central area of the tomographic chamber filled with a salt solution. Experimentally measured attenuation of the electromagnetic field through the thorax was about -120 dB. To obtain images, we used various two-dimensional and 3-D reconstruction schemes. Images of the canine were obtained. In spite of imperfections, the images represent a significant milestone in the development of microwave tomography for whole body imaging and demonstrate its feasibility.

Three-dimensional microwave tomography: experimental prototype of the system and vector Born reconstruction method

A method of image reconstruction in three-dimensional (3-D) microwave tomography in a weak dielectric contrast case has been developed. By utilizing only one component of the vector electromagnetic field this method allows successful reconstruction of images of 3-D mathematical phantoms, a prototype of the 3-D microwave tomographic system capable of imaging 3-D objects has been constructed. The system operates at a frequency of 2.36 GHz and utilizes a code-division technique. With dimensions of the cylindrical working chamber z=40 cm and d=60 cm, the system allows measurement of an attenuation up to 120 dB having signal-to-noise ratio about 30 dB. The direct problem solutions for different mathematical approaches were compared with an experimentally measured field distribution inside the working chamber. The tomographic system and the reconstruction method were tested in simple experimental imaging.

Production of carbon isotopes by laser separation

Since the advent of lasers, these unique sources of highly intense and monochromatic radiation have been proposed as excellent tools to induce or catalyze chemical reactions. Due to the great interest to the problem of isotope production, investigation and application, the laser method of isotope separation has received the most attention worldwide and may be the first major commercial application of lasers to chemistry. Laser methods of isotope separation are based on high selectivity and power of laser sources of radiation. One of the most prominent method is based on the effect is isotope-selective multiphoton dissociation of molecules by IR-radiation (MLIS-method). This phenomena was discovered in Russia in 1974 and developed from scientific investigations to industrial scale production of 13C isotopes in collaboration between the Kurchatov Institute of Atomic Energy, TRINITI and Institute of Spectroscopy of RAS. Demonstration facilities for sulfur and carbon isotope separation with average productivity up to 2 g/h have been created as a result of collaboration and these systems are aimed at optimization of MLIS process and evaluation of its cost efficiency. Experiments show that laser produced isotopes are far cheaper as compared to any conventional technique. Results of basic scientific research, existing technological cooperation allow to start building a laser isotope separation plant. Light element isotopes produced there can answer a wide variety of demands in many technologies. These isotopes can be readily used in medicine, agriculture, environmental monitoring, etc.

Heat-induced changes in optical properties of human whole blood in vitro

The effect of anomalous optical behavior of biological tissue at high-intensity laser irradiation can be caused by heat- induced changes in optical properties of consisting components, mainly muscle tissue and blood. We registered the spectral transmission of fresh human whole blood and serum samples in the wavelength range of 300 - 700 nm at the heating of samples in the temperature range of 35 - 65 degrees Celsius. The results showed an increase of 10 - 15% in the transmission of blood serum at the temperature rising up to 50 - 60 degrees Celsius. In the case of diluted whole blood a sharply enhanced transmission was observed at the temperature of 56 - 60 degrees Celsius, while further heating resulted in a decreased transmission down to the initial level. The significant changes (of a three orders of magnitude) in the transmission of whole blood at the wavelength of Nd:YAG laser (1064 nm) were observed. The obtained results can be considered as one of the possible explanations of the anomalous light distribution in certain tissues.

Laser‐induced plasma phenomena near a solid surface at the incident intensity in the range from 10 MW/cm2 to 10 GW/cm2

Results of both experimental studies and computer simulations of a laser‐induced plasma in a gas near a solid surface are presented. Particular attention is paid to two‐dimensional effects and optical properties of the plasmas with electron temperature in the range from 2 to 5 eV and electron number density from 1017 to 1020 cm−3. It is shown that to adequately describe the experimental data obtained for CO2 laser pulses with intensity of some ten MW, a computer simulation must take into account transient beam refraction in the plasma plume and, therefore, use ray tracing procedures. Comparison with the experimental results shows that the numerical model is accurate for both IR (10 μm) and UV (0.308 μm) laser wavelengths. Modulation of a TEA CO2 laser output pulse at the frequencies above 10 MHz have been observed in the case when a pulse scattered from a target passes from semi‐transparent decaying plasma near its surface. These modulations are explained using optical properties of the plasma obtained fr...

Interaction of flows of laser ablation plasmas

Our studies of laser pulsed deposition of thin films, using 20-ns second-harmonic Nd:YAG laser operated at a few GW/cm2, show that introduction of an obstacle like a grid screen into ablation plume with typical density 1018 cm−3 and temperature 3 eV substantially affects dynamics of plasma expansion and results in dramatic changes of plasma parameters. In this work, we report the effects typical for the later stage of plasma-grid interaction—effects related to the interaction of multiple plasma flows. Model experiments, performed employing method of emission spectroscopy, time-of-flight technique, and plasma imaging with CCD camera, show significant variation of plasma composition and transformation of velocity distribution due to plasmas interaction. Two modes of such transformation have been observed: linear growth of density in the resulting flow, and formation of the additional slow peak in the velocity distribution. The effect is shown to be velocity-resonant.

Intense high-repetition-rate excimer lasers and applications

Building of high average output power excimer lasers requires the solution of several complex problems. The main challenge is the creation of a uniform discharge which can be easily reproduced even at high pulse repetition rates. Some approaches to solving this problem are discussed. They resulted in creation of lasers with aperture of 4 sq cm operating at 1 kHz producing the output of 420 W at 308 nm. A large-aperture XeCl laser can produce 10 J per pulse at 50 Hz.