Abstract
The dynamic characteristics of the ions emitted from ultrashort laser interaction with materials were studied. A series of successive experiments were conducted for six different elements (C, Al, Cu, Mo, Gd, and W) using 40 fs, 800 nm Ti: Sapphire laser. Time-of-flight (TOF) ion profile was analyzed and charge emission dependencies were investigated. The effects of incident laser interaction with each element were studied over a wide range of laser fluences (0.8 J/cm2 to 24 J/cm2) corresponding to laser intensities (2.0 × 1013 W/cm2 to 6.0 × 1014 W/cm2). The dependencies of the angular resolved ion flux and energy were also investigated. The TOF ion profile exhibits two peaks corresponding to a fast and a slow ion regime. The slow ions emission was the result of thermal vaporization while fast ions emission was due to time dependent ambipolar electric field. A theoretical model is proposed to predict the total ion flux emitted during femtosecond laser interaction that depends on laser parameters, material properties, and plume hydrodynamics. Incident laser fluence directly impacts average charge state and in turn affects the ion flux. Slow ions velocity exhibited different behavior from fast ions velocity. The fast ions energy and flux were found to be more collimated.
Highlights
Dynamics of ions emission are important to study for a wide spectrum of applications either medical[1], industrial or academic, such as pulsed laser deposition[2], laser induced breakdown spectroscopy[3], laser assisted mass spectrometry[4], ion implantation[5], and light source generation[6]
We studied the TOF ion emission spectra for different elements of varying atomic mass (C, Al, Cu, Mo, Gd, and W) at different fluences starting from near ablation threshold fluence to relatively high fluences
The cleaning shots were acquired till the signal gets stable, eventually the recorded signal is a result of 10 successive laser shots. Another mechanism is that the rising edge of the laser creates a vapor, which is heated by the back end of the laser producing hot electrons due to charge separation mechanism[13]. This can not be the case since the laser pulse in our experiment (40 fs) terminates way before the energy can be transferred from electrons into the lattice to produce a vapor, this process takes several picoseconds
Summary
Dynamics of ions emission are important to study for a wide spectrum of applications either medical[1], industrial or academic, such as pulsed laser deposition[2], laser induced breakdown spectroscopy[3], laser assisted mass spectrometry[4], ion implantation[5], and light source generation[6]. Further investigations on the charged particles at higher laser fluences provided more details about their nature and their behavior Some of these studies[13,14,15] focused only on the ions revealed that two types of ions based on their energy are emitted after laser irradiation, slow and fast ions. The nature of these fast ions and their dependence on laser and target material parameters still needed to be explored, and these are the topic of this article In these experiments, we studied the TOF ion emission spectra for different elements of varying atomic mass (C, Al, Cu, Mo, Gd, and W) at different fluences starting from near ablation threshold fluence to relatively high fluences. Preliminary modeling was provided for better understanding and explanation of these experimental results
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