ABSTRAKT

Our goal is to develop an optical spectroscopy analysis of toxic molecular compounds by using the atomic emission of a plasma induced by a Nd:YAG laser (TRELIBS). The qualitative and quantitative analysis have been carried out on chlorine and fluorine atoms from organohalogenated molecules. The experimental setup uses a Nd:YAG laser at 1064 nm and a cylindrical cell in stainless steel through which the gas flow is introduced. The laser beam is focused in the cell through a BK7 lens, while the emission wavelengths are analyzed by a 24 optical fiber probe connected to a spectrometer with an optical multichannel analyzer, and a computer. The time resolution of plasma emissions with a gated image intensifier leads us to a best signal to noise ratio (SNR) on atomic emission lines with 0.5 to 4 μs delay between the end of the laser pulse and the detector aperture. Spectral, time and space resolution permit a high reproducibility and a good sensitivity of the method (close to 10 ppm(w/w)).
The high temperature of the plasma produced by a laser beam of 100 mJ is responsible of the total decomposition of the molecular structure and explains the high excitation states of the atoms such as Cl, F, S, P.