RESUMEN
An 1. 06 microm Nd : YAG laser beam (energy: -500 mJ/pulse, pulse width: 10 ns, repetition rate: 30 Hz) was focused by a conical lens, and a column of laser-induced air plasmas (LIAP) came into being. The LIAP column, about 8 cm of long and 5 cm in maximal diameter, was studied by spectra measurement. The spectra of the LIAP column at different position were measured in the directions both perpendicular and parallel to the laser propagation respectively. From these data, the electron densities of the LIAP were evaluated. The experimental results indicate that the LIAP formed in an olivary shape, i. e. , symmetrical in the vertical direction but unsymmetrical in the horizontal direction, and the maximal electron density is about 10(18) cm(-3). The spatial distributions of atoms, molecules and ions in different states in the LIAP were also discussed, and provide clues for discovering the microstructure of LIAP.
RESUMEN
The time-resolved spectra of the air-breakdown plasma produced by the 1.06 microns beam of a Nd:YAG laser were investigated by using the time-delayed spectra and the spectral line evolution methods. The time evolutions of the short wavelength band and long wavelength band of the continuous spectra of the air-breakdown plasma have been measured. The result shows that the decay rates of both bands are slowing down 0.5 microsecond after the excitation of the plasma, and the attachment and the detachment of free electrons by O2 in the plasma could be the reason for this behavior. The results of the time-resolved measurements of the line spectra show that most of the line spectra have the evolution time longer than their lifetimes, and the evolutions of some line spectra take a fashion of "decay-grow-decay". We consider these evolution behaviors of the line spectra to be related to various recombination processes and the energy transfer processes of the decaying plasma.