Effects of High-Pressure Buffer Gases on Emission from Laser-Induced Plasmas

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Abstract
A laser-induced plasma is used for atomization, ionization, and excitation of elements in solid samples. The analytes are placed in a variable-pressure chamber in which the surrounding gas can be modified to obtain optimum emission characteristics for a particular sample. A time-resolved system is described which can produce qualitative and semi-quantitative spectroscopic information using a single laser plasma. The effects of the plasma position relative to the sample, the chamber pressure, and the characteristics of the surrounding gases are studied. When helium was employed as the buffer gas, maximum emission intensity for the aluminum ionic transition at 281.6 nm was observed. The spectra obtained show that it is possible to obtain qualitative spectroscopic information with the formation of single plasmas by the use of time resolution. It is also demonstrated that sample excitation can be achieved directly by the plasma and indirectly by energy transfer from gases in the chamber. This method allows the use of small sample quantities with little sample preparation and is especially advantageous for solid samples which are not easily dissolved.