Spectroscopic investigation of laser-initiated low-pressure plasmas in atmospheric gases.
Laser-initiated breakdown of N2, O2, and Ar has been investigated at sub-atmospheric pressures using a pulsed (10-nsec) Nd:yttrium aluminum garnet (Nd:YAG) laser at 1.06 μm. Breakdown thresholds have been determined from 3 to 760 Torr, and spectral analysis of the plasma emission has been carried out at 10 and 125 Torr over the 300–600-nm range. Sharp spectral features arising from highly excited singly and multiply charged ions are reported as well as an underlying continuum at intermediate pressure. Time-resolved measurements indicate a complex kinetic dynamic optical behavior.
Infrared Plasma Emissions.
Abstract : In this final report, we present the infrared spectrum of a laser produced oxygen plasma. We have focused on extending the spectral range of observation of Ol Rydberg emissions to 13 micrometers. We report the first observations of OI Rydberg line emission in the 8-13 micrometer wavelength region. We also present observations of Bremsstrahlung emission that compare favorably with recent theoretical results of Lin. We have developed a model called APOSTLE which predicts the line broadened emission spectrum from an OI plasma. We describe the theoretical and functional basis for the model. The model results are discussed and compared with the data obtained in the plasma experiment.
Structure of the plasma fireball produced by a CO2 laser.
The space and time resolved structure of a helium plasma produced with a repetitive CO2 laser is studied during the first 15 μsec of the afterglow period. The spectra of several neutral and ionized helium lines are used in the determination of the density and temperature profiles of the luminous fireball. It is found that the plasma is comprised of a dense, hot core which emits primarily ionic lines, and a well‐defined tenuous outer shell which is primarily the source of neutral emission lines. This “two‐component” plasma structure develops at ∼0.4 μsec after breakdown, at about the time when the luminous fireball dissipates its expansion energy and comes to a virtual standstill.