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

Domenico Delle Side,Anna Paola Caricato,Josef Krása,L Torrisi,Vincenzo Nassisi,M Cutroneo

doi:10.1051/epjconf/201816704006

Abstract

The exposure of a target to a focused laser beam results in the occurrence of a time-varying current between the target itself and the grounded vacuum chamber. This current is composed by three distinct phases, namely the ignition phase, in which the laser pulse drives the electron emission, while electrons coming from the ground through the target holder balance the positive charge generated on the target. The active phase appears at post-pulse times and it is characterized by the presence of peaked structures in the time-resolved current, representing characteristics of the target composition. Lastly, the afterglow phase is determined by a current of electrons flowing from the target to the ground. During the active phase of the target current resulting from polymers ablation with an UV KrF laser, negative target current peaks are observed, whose origin is still unknown. We investigate the dependence of these current structures on the dimensions of the target, using ultra-high molecular weight polyethylene disks of different thickness.

Highlights

The interaction of an intense laser pulse with a solid target give rise to a series of complex phenomena that eventually ends with ejection of vaporized and ionized material from the target surface
The active phase appears at post-pulse times and it is characterized by the presence of peaked structures in the time-resolved current, representing characteristics of the target composition
Instead, we found that Target current (TC) assumes negative values during the ignition phase [15, 16]

Summary

Introduction

The interaction of an intense laser pulse with a solid target give rise to a series of complex phenomena that eventually ends with ejection of vaporized and ionized material from the target surface. Depending on the the laser pulse length, the physical processes underlying the ejection could change [1]. Neverthless, ejecta are readily created after the first moments of the laser pulse, both as neutral particles and ions, electrons being the first. The escape of charged particles from the target generates a return current from ground that balances such process. Target current (TC) is a relatively unexplored phenomenum in the field of laser-matter interaction. The initial studies started in the late seventies [2, 3] and continued in a patchy fashion across the following decades [4, 5] until recently

Methods

Results

Conclusion