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24 April 2019 Target return current in low‐intensity laser target interaction
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Laser-target interaction experiments demonstrated that the return target current, jTC(t), which neutralizes the target charge appearing when the fastest electrons escape the plasma, is one of principal characteristics of the laser-matter interaction. jTC(t) flowing between the target and the ground is emerging just when the laser intensity exceeds the threshold intensity of the plasma formation. The experimental determination of the number of escaped electrons is primarily based on precise target current observations. We present the experimental observation of jTC(t) neutralizing metallic and plastic targets irradiated with low intensity ranging from 108 to 1013 W/cm2 delivered by KrF and iodine lasers operated at 248-nm and 1315-nm wavelengths, respectively. Our experiments show that the charge appears on targets continuously not only during the laser-plasma interaction but also during the plasma expansion into the vacuum. The analysis of jTC(t) allows us to determine the level of influence of the target surface pollution by chemisorbed hydrocarbons on the plasma production, which is also needed for elucidation of specific processes leading to the target charge and ion emission. Very specific feature of jTC(t) was found for plastic targets. Our experiments also demonstrate that the accompanying phenomenon of low-intensity laser-target interaction is the generation of electromagnetic pulses that are emitted at frequencies coinciding also with the resonant frequency modes of the interaction vacuum chamber.
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Josef Krása, Daniel Klír, Karel Řezáč, Jakub Cikhardt, Miroslav Pfeifer, Jan Dostál, Roman Dudžák, and Vincenzo Nassisi "Target return current in low‐intensity laser target interaction", Proc. SPIE 11035, Optics Damage and Materials Processing by EUV/X-ray Radiation VII, 110350G (24 April 2019);

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