Spectroscopy of laser plumes for atto-mole and ng/g elemental analysis

Two all-optical analytical techniques are reviewed. Both are capable of highly sensitive multi-element analysis. One is by means of resonance-enhanced plasma spectroscopy. It minimizes the continuum background associated with laser-induced plasmas. Relative to laser-induced breakdown spectroscopy, the signal-to-noise ratio is improved by orders of magnitude, thus allowing the quantitation of sodium and potassium at the single blood cell level. The other technique utilizes laser-excited atomic fluorescence. It has been traditionally handicapped by its one wavelength-one transition specificity. We showed, however, that numerous elements could be induced to fluoresce at a single excitation wavelength of 193 nm provided that the analytes were imbedded in dense plumes, such as those produced by pulsed laser ablation. This method eliminates the continuum plasma background and sub-ppb sensitivity was demonstrated in the analysis of aqueous lead colloids.