When a 10–100-mJ single-spike Q-switched Nd laser pulse is focused on a copper sample, the presence of an atmosphere affects the spectra, the crater size, and the amount of sample vaporized. At 760 Torr the crater diameter (90 μ) and amount of sample vaporized (35 ng) remain relatively constant while at 1 Torr they both increase with increasing laser energy. Spatial changes in the spectra occur with changes in ambient pressure. The continuum intensity of the limited region just above the sample surface appears to be a better measure of the energy reaching the sample than does the energy of the laser beam. The experimental results appear to be caused by absorption of a large fraction of the laser energy in an atmospheric plasma. A radiation-supported shock-wave model is evaluated in detail and compared briefly with similar models as possible mechanisms for production of the atmospheric plasma. The analytical chemical implications of the experimental and theoretical results are discussed.
E. H. Piepmeier and D. E. Osten, "Atmospheric Influences on Q-Switched Laser Sampling and Resulting Plumes," Appl. Spectrosc. 25, 642-652 (1971)