Dynamics of ions produced by laser ablation of several metals at 193 nm

Abstract

Influence of excited state spatial distributions on plasma diagnostics: Atmospheric pressure laser-induced He-H2 plasma J. Appl. Phys. 112, 083302 (2012) Characterizing the energy distribution of laser-generated relativistic electrons in cone-wire targets Phys. Plasmas 19, 103108 (2012) Verification of the physical mechanism of THz generation by dual-color ultrashort laser pulses Appl. Phys. Lett. 101, 161104 (2012) ORION laser target diagnostics Rev. Sci. Instrum. 83, 10D732 (2012) Target normal sheath acceleration sheath fields for arbitrary electron energy distribution Phys. Plasmas 19, 083115 (2012) Additional information on J. Appl. Phys. This work reports the study of ion dynamics produced by ablation of Al, Cu, Ag, Au, and Bi targets using nanosecond laser pulses at 193 nm as a function of the laser fluence from threshold up to 15 J cm À2 . An electrical (Langmuir) probe has been used for determining the ion yield as well as kinetic energy distributions. The results clearly evidence that ablation of Al shows unique features when compared to other metals. The ion yield both at threshold (except for Al, which shows a two-threshold-like behavior) and for a fixed fluence above threshold scale approximately with melting temperature of the metal. Comparison of the magnitude of the yield reported in literature using other wavelengths allows us to conclude its dependence with wavelength is not significant. The evolution of the ion yield with fluence becomes slower for fluences above 4-5 J cm À2 with no indication of saturation suggesting that ionization processes in the plasma are still active up to 15 J cm À2 and production of multiple-charged ions are promoted. This dependence is mirrored in the proportion of ions with kinetic energies higher than 200 eV. This proportion is not significant around threshold fluence for all metals except for Al, which is already 20%. The unique features of Al are discussed in terms of the energy of laser photons (6.4 eV) that is enough to induce direct photoionization from the ground state only in the case of this metal.

Ion generation and loading of a Penning trap using pulsed laser ablation

“…Previous studies on the laser ablation of beryllium are sparse [22,23]. Aluminum however has been the subject of several ablation studies using time-of-flight [24][25][26] and charge collection measurements [22,[27][28][29]. In all of these studies, significant ion production was typically observed for laser fluences around 1-2 J cm −2 .…”

Langmuir probe measurements and mass spectrometry of plasma plumes generated by laser ablation of La0.4Ca0.6MnO3

“…With a positive bias, electrons can reach the probe surface, giving rise to a negative current, the value depending on the bias voltage and the TOA. As has been observed before, the magnitude of the detected negative current signals greatly exceeds the positive current signals, due to the much lower electron mass [4][5][6][7]. With decreasing laser fluence, the amplitudes of the positive and negative current signals decrease, while their arrival times are delayed, indicating a decrease in the amount and expansion velocity of the laser ablation plume.…”

“…4 Langmuir probe analysis is most suitable when one ionic species is dominant, as is the case for ablation of an elemental metal target. 5 However, for many PLD applications compound targets with a complex chemical composition are used and different ionic species are present in the plasma, all of which contribute to the ion current signal in a Langmuir probe measurement. Mass spectroscopy may be used to distinguish different ion masses and charge.…”

“…Langmuir probe measurement is a relatively simple and direct plasma diagnostic technique. [4][5][6][7][8][9][10] A small metal probe with variable bias voltage is placed in the flowing ablation plasma, and, depending on the polarity of the bias, an electron or positive ion current is collected as the plasma flows past the probe leading to the time-of-arrival (TOA) distribution. The TOA distributions usually show the presence of a smooth current signal for both elemental and multi-component target.…”

Interpenetration and stagnation in colliding laser plasmas

“…We used different target materials (C, Al, Mo, W) for this study to get a better understanding of when and where interpenetration or stagnation happens at the colliding interface. 29 In laser produced plasmas, the physical and chemical properties 30,31 of the target are one of the governing factors determining the ion charge state, velocity, particle density, etc. Hence, depending upon the target material, the generated plume's ion emission features (velocity, flux) as well as plasma properties (temperature, density) will vary even at constant laser intensity.…”