ISSN 1063-780X, Plasma Physics Reports, 2013, Vol. 39, No. 8, pp. 668–673. © Pleiades Publishing, Ltd., 2013. Original Russian Text © N.G. Borisenko, Yu.A. Merkul’ev, A.S. Orekhov, S. Chaurasia, S. Tripathi, D.S. Munda, L.J. Dhareshwar, V.G. Pimenov, E.E. Sheveleva, 2013, published in Fizika Plazmy, 2013, Vol. 39, No. 8, pp. 752–758. 668 1. INTRODUCTION About 20 years ago, theoretical and experimental studies of plasmas born on low-density 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 low-density organic substances from other low-den- 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 three-dimensional (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 path of the laser beam [10–12]. In those works, such transmission was attributed to substantial fluctuations of the plasma density and temperature in turbulent plasma just after the beginning of the laser pulse. Until the experiments reported in the present paper were carried out, it was unclear what is the reason for the discrepancy between the results of the first experi- ments [3, 5], in which less than 0.5% of the laser energy penetrated through the plasma, and recent experiments [11, 12], in which transmission of the energy of a laser pulse with a shorter duration, shorter wavelength, and higher intensity of about 5 × 10 14 W/cm 2 reached 1–5%. Our experiments were performed at a neodymium laser facility with a 0.5-ns pulse duration and 10 14 -W/cm 2 intensity on the target. 2. EXPERIMENTAL SETUP The experiments were performed at the laser facil- ity of the Bhabha Nuclear Research Centre. The laser is capable of generating one 16-J laser pulse per 20 min. Laser radiation at the main wavelength of 1.064 μm was gathered into a 100-μm-diameter focal spot. The scheme of the experiment is shown in Fig. 1. The energy balance was measured using four calo- rimeters (E1–E4). Calorimeter E1 was used to moni- tor the energy of the heating beam, calorimeter E2 measured the energy of backscattered radiation (pre- LASER PLASMA Specific Features of Microheterogeneous Plasma Produced by Irradiation of a Polymer Aerogel Target with an Intense 500-ps-long Laser Pulse N. G. Borisenko a , Yu. A. Merkul’ev a , A. S. Orekhov a , S. Chaurasia b , S. Tripathi b , D. S. Munda b , L. J. Dhareshwar b , V. G. Pimenov c , and E. E. Sheveleva c a Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia e-mail: orekhov@sci.lebedev.ru b High-Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai-85, 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 (10 14 W/cm 3 ) short (0.5 ps) 1.064-μm 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 X-ray emission. DOI: 10.1134/S1063780X13080035