Specific features of microheterogeneous plasma produced by irradiation of a polymer aerogel target with an intense 500-p
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Specific Features of Microheterogeneous Plasma Produced by Irradiation of a Polymer Aerogel Target with an Intense 500pslong Laser Pulse N. G. Borisenkoa, Yu. A. Merkul’eva, A. S. Orekhova, S. Chaurasiab, S. Tripathib, D. S. Mundab, L. J. Dhareshwarb, V. G. Pimenovc, and E. E. Shevelevac a
Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia email: [email protected] b HighPressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai85, India c Zelinksy Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii pr. 47, Moscow, 119991 Russia Received May 24, 2012; in final form, January 23, 2013
Abstract—The properties of microheterogeneous plasma produced by irradiation of a polymer aerogel target with an intense (1014 W/cm3) short (0.5 ps) 1.064µm laser pulse were studied. It is found that, even at plasma densities exceeding the critical density, a small fraction of the incident laser radiation penetrates through the plasma in which the processes of density and temperature equalization still take place. The intensification (as compared to plasmas produced from denser foams and solid films) of transport processes in such plasma along and across the laser beam can be caused by the initial microheterogeneity of the solid target. The replacement of a small (10% by mass) part of the polymer with copper nanoparticles leads to a nearly twofold increase in the intensity of the plasma Xray emission. DOI: 10.1134/S1063780X13080035
1. INTRODUCTION About 20 years ago, theoretical and experimental studies of plasmas born on lowdensity structured materials [1–5], such as polymer foams, began. Advanced diagnostic complexes [5, 6–8] allowed the research teams to acquire detailed information on plasma processes and coefficients of energy transfer in such plasmas. Over this time period, diagnostic instru ments and laser facilities were substantially upgraded and a technology was developed to produce advanced targets made of polymer aerogels. The term “aerogel” was introduced in [8] in order to distinguish specific lowdensity organic substances from other lowden sity solid materials, such as ultradisperse metals and graphitized and composite materials, which altogether are often called foams. Aerogels differ substantially in their properties and methods for their production, especially if, along with the low density, it is necessary to provide the required fine structure with a given degree of homogeneity and high reproducibility of tar gets over a long time period. Aerogel targets consist of a threedimensional (3D) polymer network with micron distances between fibers, the mean fiber diam eter being about 50 nm [8–10]. Due to development of the diagnostic equipment and technology for target production, it became possible to detect transmission of laser radiation through plasma in the initial stage of laser–plasma interaction and the associated heating of the substrate foil placed behind the polymer layer on
the optical pat
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