Subthreshold Laser Ablation Measurements by Langmuir Probe Method for ns Irradiation of HfO2 and ZrO2

Abstract

The unbiased Langmuir probe (LP) method was used to perform measurements on HfO2 and ZrO2 samples around the laser ablation threshold on a wide range of irradiation conditions. Important changes in the lifetime (from ms to μs) and the shape of the charge particle current were seen with the increase of the laser fluence. The ablation threshold was estimated by evaluating the overall average ablated charge as a function of the laser fluence. Above the ablation threshold, the generation of high kinetic species is seen, which can reach several keV. An important jump in ion acceleration potential is observed for values above 1 J/cm2, which coincides with the dominant presence of negative ions in the plasma. The evolution of several plasma parameters (ion density, expansion velocity, electron temperature, Debye length) was investigated and correlated with the fundamental ablation mechanism involved in various irradiation regimes. The LP data were correlated with COMSOL simulations on the maximum surface temperature reached during irradiation. Important correlations between the evaporation and melting processes and ablation threshold fluence and ion acceleration phenomena are also reported.

Exploring fs-laser irradiation damage subthreshold behavior of dielectric mirrors via electrical measurements

“…In our previous work [ 20 ] , we have shown that LP signal can be used to quantify the ablation threshold value by using the average current representation as a function of the laser fluence. Here we expand the procedure by analyzing the variation of the ejected charge (Figure 4(a)) and the sample compensation charge (Figure 4(b)) as a function of laser fluence.…”

“…The scenarios for material removal from the target follow a complex interconnectivity of electrostatic and thermal mechanisms, which are temporally and spatially separated: the first stages of laser ablation are of an electrostatic nature, while the second stages are of a thermal nature. In our previous work [ 20 ] , we have shown that the Langmuir probe (LP) is a suitable technique for estimating the nanosecond ablation threshold limit as it detects contributions from each stage [ 21 ] . Other reports focus on LP measurements of ablation threshold in the ns regime [ 22 ] , while reports on the detection of the fs-incubation stage emphasize the necessity of having a minimum of 10,000 pulses to estimate the threshold [ 23 ] .…”