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- Double ionization (2) (entfernen)
The emission from doubly ionized species in laser-induced plasmas has not been properly investigated before since most analytical measurements were made at relatively long delays. This work proves that doubly ionized species, such as boron (B) III and iron (Fe) III, can exist during the first 150200 ns of the plasma lifetime in plasmas produced in air by typical lasers with irradiances of 109 1011 W/cm². The emission from these ions was detected using both the double- and single-pulse excitations.
The sum of the second ionization potential and the energy of corresponding excited states is approximately 30 eV. The presence of doubly charged ions in the early plasma was additionally confirmed by computer simulations using a collision-dominated plasma model. The Emission from doubly ionized species may be used for analytical purpose. For example, in the spectrum from a B–Fe ore, the B III analytical line at 206.6 nm is free from Fe spectral interference thus enabling the online laser-induced breakdown spectroscopy sorting of ores into three products with high, medium, and low B2O3 contents.
Comparison of single and double-pulse excitation during the earliest stage of laser induced plasma
(2011)
This paper deals with comparison of single-pulse (SP) and double-pulse (DP) excited plasmas during their earliest phase of life, from 0 to 500 ns. The samples are Si and Al and the irradiance per pulse is approximately 20 GWcm-2 under ambient conditions. It was found that at the beginning of a plasma lifespan, Si III and Al III ions were excited even under the SP excitation conditions and became much more abundant under DP excitation. The lifetime of doubly-ionized species was found to be very short, and after a delay of 200–300 ns they were not detected. The DP plasma differs from the SP plasma by the intensity of continuum radiation and by the width of emission lines, which are substantially narrower in the DP plasma. The intensity of light emitted from singly and, especially, doubly-ionized species is higher compared with neutral atoms; whereas the decay time of both neutral and ionized species is longer. An excitation mechanism for the DP plasma is proposed enabling qualitative and a quantitative explanation of the experimental data.