Time-resolved plasma emission spectrum analyses at the early stage of laser ablation

Time-resolved plasma emission spectra are analyzed during pulsed laser ablation of solid materials. At early stage for delay time less than 200 ns, individual spectral lines an superimposed on a continuum spectrum, which disappears gradually as delay time increases. Spectral line widths decrease obviously and the peak positions shift to the shorter wavelengths at the same time. Ion spectral lines disappear earlier than the excited atoms due to plasma recombination. Dependence of the emission spectra on laser fluence, probe distance and chamber pressure is also discussed. Spectral line intensities increase with laser fluence and tend to saturate at a high laser fluence due to plasma shielding effect. Most of the spectral line broadening and peak shift take place near the substrate surface. Excited atoms dominate in the plasma inner layer while the outer layer is mostly occupied by the ions at the early stage. Plasma flying speeds are estimated. Spectral line intensity increases with chamber pressure. Electron density as a function of delay time is also studied. (C) 2000 Elsevier Science B.V. All rights reserved.