Target return current in low‐intensity laser target interaction

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 lasertarget interaction is the generation of electromagnetic pulses that