Characteristics of target polarization by laser ablation

Abstract

Experimental results are obtained concerning the target polarization, which aptly characterizes the laser ablation. The charge separation in the laser-produced plasma, structure of the ion front, and the current of fast electrons expanding into the vacuum chamber ahead of ions are of crucial importance for the interpretation of multi-peak structure of target currents appearing much later than the laser pulse. Of particular interest is the correlation between the partial maxima in the time-resolved target current and the square root of mass number of ionized species. The late-time negative charging of targets provides evidence for production of very slow ions by ionization of neutrals ablated at the target crater by radiation from plasma produced by 23 ns excimer krypton fluoride laser.Keywords: Target current in laser-produced plasmas; positive and negative target polarization; space structure of ion front

On the origin of negative target currents during laser ablation of polyethylene

“…This confirms that charge unbalance on the target surface is able to attract electrons also in the absence of any electric field between T and FC. Consequently P2 exist irrespectively of any bias voltage on FC, as reported in [14]. This explains also because the "optimal thickness" affects also P2.…”

“…Lastly, the afterglow phase is determined by a current of electrons flowing from the target to the ground. Furthermore, changing the target material, we showed that the occurrence in time of current peak in the active phase is strongly related to the charge-to-mass ratio of the generated ion species [14], i.e.…”

“…The duration of target neutralization with ground electrons reflects the duration of electron escape from the expanding plasma [14]. The TC occurs when the laser pulse starts to produce the plasma [11,13].…”

Multi probes measurements at the PALS Facility Research Centre during high intense laser pulse interactions with various target materials

“…While the target current probe (T-Probe) allowed us to determine occurred current onto the target as well as magnetic field around the target holder, loop antennas and linear antennas were employed for measurements of electric field and magnetic field both inside and outside the interaction chamber. The escaping electrons generate up to hundreds kV potential at the target and 10kA current flows from the target to the ground [9][10][11][12]. The return current, that compensates the net positive target charge, generates an electromagnetic pulse because the system target-target holder is in first approximation a linear antenna emitting toroidal radiation pattern in the far-field and more complex field pattern in the near field zone [13][14][15][16][17][18][19][20].…”

Strong electromagnetic pulses generated in laser-matter interactions with 10TW-class fs laser

“…Such pulses strongly interfere with the data acquisition systems and may pose a threat to safe and reliable operation of high-power, high-intensity laser facilities, so it is no wonder that mechanisms for their generation continue to attract attention [7][8][9][10][11][12][13][14]. In particular, in a series of recent articles [7][8][9] attention was given to the phenomenon of electric polarization of the target as a result of lasertarget interaction, and the effect of EMP generation via the target neutralization current.…”