Separate reconstruction of the speed of sound,density of the medium,and coefficient of absorption in tomographic problems

A procedure is proposed for separating contributions to the scatterer function by inhomogeneities of the speed of sound, density of a medium, and coefficient of absorption. The scatterer function is reconstructed by solving the inverse problem. The power index of the absorption coefficient’s frequency dependence is determined simultaneously. The resistance to interference of this procedure is investigated by simulations in the multifrequency mode.     

Experimental-calculation simulation of the ejection of particles from a shock-loaded surface

The possibilities of measuring complex Pylenie, which is intended for studying the parameters of the particles ejected from the free surface of a shock-loaded material and was created at the Institute of Experimental Gas Dynamics and Detonation Physics RFNC-VNIIEF, are demonstrated. The operation of the complex is based on the following three methods, which are based on different physical principles and supplement each other: laser-optical method (macro- and microfilming), pulsed X-ray method, and piezoelectric pressure sensors. This complex is used to study the ejection of particles from the free surface of lead samples when a shock wave with a pressure of 7, 16, and 23 GPa at its front reaches this surface. The effect of the surface roughness and the pressure amplitude at the shock wave front on the quantitative characteristics of the process is shown. The calculation-theoretical simulation is performed by two-dimensional numerical calculations of gasdynamic flows, and the calculation results are used to estimate the “ejecta” characteristics in terms of the developed phenomenological model of the process.     

On the Nature of Defects in Solid Structure under the Action of Laser Radiation with the Energy Not Destructing a Sample as a Whole

Nature of the defects in solid samples generated under the surface irradiation by a pulse of a CO₂-laser is investigated by the method of acousti©emission analysis. The laser pulse energy of 1.5 J was insufficient for destroying the sample. The samples were rods made from crystal (aluminum, copper) or amorphous (glass) materials. Acoustic emission signals from a rod face were studied which arise under the action of the laser radiation focused onto the opposite face of the rod. Analysis of data obtained shows that local structural changes arise in all the samples investigated. Defects in the form of microscopic cracks have been generated, and in the case of glass (the most fragile material), the cracks existing prior to irradiation have been developed.