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.

Microwave tomography: two-dimensional system for biological imaging.

Microwave tomographic imaging is one of the new technologies which has the potential for important applications in medicine. Microwave tomographically reconstructed images may potentially provide information about the physiological state of tissue as well as the anatomical structure of an organ. A two-dimensional (2-D) prototype of a quasi real-time microwave tomographic system was constructed. It was utilized to reconstruct images of physiologically active biological tissues such as an explanted canine perfused heart. The tomographic system consisted of 64 special antennae, divided into 32 emitters and 32 receivers which were electronically scanned. The cylindrical microwave chamber had an internal diameter of 360 mm and was filled with various solutions, including deionized water. The system operated on a frequency of 2.45 GHz. The polarization of the incident electromagnetic field was linear in the vertical direction. Total acquisition time was less than 500 ms. Both accurate and approximation methods of image reconstruction were used. Images of 2-D phantoms, canine hearts, and beating canine hearts have been achieved. In the worst-case situation when the 2-D diffraction model was used for an attempt to "slice" three-dimensional (3-D) object reconstruction, we still achieved spatial resolution of 1 to 2 cm and contrast resolution of 5%.

TIR-1 carbon dioxide laser system for fusion.

During recent years pulsed CO(2) lasers for fusion research have been under construction in the I. V. Kurchatov Institute of Atomic Energy and the D. V. Efremov Electro-Physical Apparatus Institute. Efforts are being concentrated at present on two approaches: (1) microsecond laser pulse plasma heating in solenoids and theta pinches (UTRO system) and (2) nanosecond CO(2) laser utilization for inertial confinement fusion. The TIR-1 system was created to develop nanosecond CO(2) laser technology and to study laser-target interaction at 10 microm. This system is designed to deliver ~1-kJ energy in one beam of ~l-nsec duration. The TIR-1 system consists of an oscillator-preamplifier system that produces an ~1-nsec laser pulse with an energy contrast ratio of ~10(6), a large-aperture (30 x 30-cm(2)) triple-pass amplifier capable of providing approximately 1 kJ in a 1-nsec pulse, a target chamber with diagnostic equipment, and associated engineering systems.

Average power limitations in high-repetition-rate pulsed gas lasers at 10.6 and 16 microm.

Processes resulting in average power limitations in high-repetition-rate pulsed lasers are studied. The description and performance of a CO(2) laser with an average power up to 10 kW as well as of an optically pumped CF(4) laser are given.