SPECTROCHEMICAL ANALYSIS OF LIQUIDS USING LASER-INDUCED PLASMA EMISSIONS - EFFECTS OF LASER WAVELENGTH ON PLASMA PROPERTIES

We spectroscopically determined the temperature and electron density o f the plasma plumes produced by pulsed-laser ablation of aqueous solut ions containing sodium, lithium, and rubidium. With the use of a Nd:YA G laser at 532 nm and fluence of 3 J/cm(2), the plasma produced was ho t (low eV range) and extensively ionized, with electron density in the 10(18) cm(-3) range. Analyte line signals were initially masked by in tense plasma continuum emissions and would only emerge briefly above t he background when the plume temperature dropped below 1 eV during the course of its very rapid cooling. Since ionization was thermally indu ced, the intense plasma flash was inevitable. In contrast, 193-nm lase r ablation at similar fluence generated plasmas of much lower (< 1 eV) temperature but comparable electron density. Plasma continuum emissio ns were relatively weak, and the signal-to-background ratio was a thou sand times better. Consequently, this ''cold'' plasma was ideal for sa mpling biologically important elements such as sodium, potassium, and calcium.