Abstract

Single-mode laser diodes of the etalon-type generate radiation of very narrow bandwidth, typically 0.04 nm, in the red and near-infrared wavelength range [1]. The linewidth of such diodes is considerably narrower than the line widths of free atoms in thermal atomizers, analytical flames, or plasmas. Therefore, these laser diodes are proper tools for analytical high-resolution laser spectroscopy. The necessary condition for high-resolution measurements is the atomization of the samples in low-pressure atmospheres (≤ 10 hPa), where pressure broadening of the analyte lines is small and line broadening is dominated by the Doppler effect. If the shifts of spectral lines by the isotope effect are larger than the Doppler-widths of the individual components, the isotope composition of the elements can be measured by Doppler-limited laser spectroscopy. This is often sufficient for light and heavy elements, where large isotope line shifts occur due to the classical Bohr mass shift or due to the volume or field shift, respectively. For medium heavy elements the dominating contribution to isotope shift is the relatively small specific mass shift. This means in general, that for these elements Doppler-free spectroscopic methods are required, such as saturation spectroscopy or Doppler-free two photon excitation [2].

© 1998 Optical Society of America