A TEA CO<sub>2</sub> laser beam (500 mJ, 100 ns) has been focused on a Zn target at reduced ambient gas pressures. In order to confine the laser plasma into a limited space, a tube (7 × 7 × 20 mm) has been placed just in front of the target, and the laser beam has been focused through the tube of the target. The time-resolved spatial distributions of Zn emission lines show that emission intensity increases quickly with a distinct jump near the front of the plasma and that the emissions take place only in a limited thin layer. It is also shown that the displacement of the emission front is proportional to 0.6 power of time. These experimental results support the supposition that the plasma is excited by a plane shock wave induced by the laser bombardment. This laser plasma confinement technique shows the possibility of improving the sensitivity in laser microprobe spectrochemical analysis.
K. Kagawa, M. Tani, H. Ueda, M. Sasaki, and K. Mizukami, "TEA CO2 Laser-Induced Plasma with a Plane Shock Wave Structure," Appl. Spectrosc. 47, 1562-1566 (1993)