Abstract

The air-acetylene burner is commonly used as an atomization source for elemental analysis with various spectroscopic methods, ranging from flame emission to sophisticated laser-based techniques. The latter include laser-induced fluorescence, laser-enhanced ionization, polarization saturation spectroscopy, and degenerate four-wave mixing. All of these techniques exhibit excellent sensitivity for trace elements in water, typically in the parts per billion range or better. The spectral resolution, however, is limited to about 5 GHz because the spectral lines are broadened by collisions in the atmospheric pressure flame. We have developed a low-pressure interface that allows a hundred-fold improvement in resolution while retaining the sensitivity and convenience of flame atomization. We have tested the apparatus by studying the spectrum of the sodium D lines, using a type of saturation spectroscopy. We have been able to separate hyperfine transitions and crossover resonances with a resolution of better than 50 MHz. A recognizable hyperfine spectrum can be obtained with as little as 100 ppb of sodium.

© 1987 Optical Society of America