We studied the confocal double-pulse laser-induced plasma in the very beginning of its life. It was found that the second laser pulse fired 0.7 to 5 µs after the first pulse produces plasma which, during the first 0 to 20 ns, resembles solar configuration. There is a very hot and compact plasma core that radiates a broad continuum spectrum and a much larger and cooler outer shell. The light from the hot core passes through the cold outer shell and is partly absorbed by atoms and ions that are in ground (or close to ground) states. This produces absorption lines that are similar to Fraunhofer lines observed in the sun spectrum. The possibility to use these absorption lines for new direct and calibration free laser-induced breakdown spectroscopy analytical applications, both in laboratory and industrial conditions, is proved.
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Spontaneous transition probabilities from National Institute of Standards and Technology (NIST) [21]. is the lower level energy ; is the transition probability between upper level and lower level ; are the multiplicity of lower and upper levels, respectively.
From Kurucz and coworkers [22].
and are the lower and upper levels energies in , is the oscillator strength of the transitions, and and are the multiplicity of low and upper levels, respectively.
Table 3.
Initial Conditions in Plasma Computer Simulations
, cm
, K
V, Mach
Delay, ns
Gate, ns
Interpulse, ns
Si
0.02
0.5
80000
2
0, 5, 10, 40
0.1
1000
Pb
0.02
3.5
80000
2
5, 10, 15, 100
1
1000
Tables (3)
Table 1.
Fraunhofer Lines and Spectroscopic Parameters Revealed in the Present Papera
Spontaneous transition probabilities from National Institute of Standards and Technology (NIST) [21]. is the lower level energy ; is the transition probability between upper level and lower level ; are the multiplicity of lower and upper levels, respectively.
From Kurucz and coworkers [22].
and are the lower and upper levels energies in , is the oscillator strength of the transitions, and and are the multiplicity of low and upper levels, respectively.