Confinement effect in TEA CO2 laser-induced plasma on solid organic samples

A Transversely Excited Atmospheric (TEA) CO2 laser beam (500 mJ, 200 ns) was focused on soft solid organic compounds under a low-pressure surrounding gas at around 2 Torr. We found that in order to induce a laser plasma from solid organic sample, such as plastics, the ablated atoms must be confined in a small hole (diameter of about I mm and depth of around 1-2 mm). Using our unique technique of density jump measurement (]Rainbow Interferometer), we proved that the plasma is excited by a shock wave and that the confining hole works to induce and enhance a strong shock wave. The plasma has favorable characteristics for spectrochemical analysis due to its low spectral background and sharp emission lines; hence, the spectra can be taken using optical multichannel analyzer (OMA) without gated mode. By using the confinement effect, we detected chlorine ionic lines (Cl 11 at 479.4 urn, Cl 11 at 481.0 nm, and Cl 11 at 481.9 nm) with relatively strong emission intensities in the plastic sample containing chlorine.