Multiphoton Ionization Via an Excited State; A Survey of its Effect on Laser Breakdown in the Atmosphere
Abstract
The program on controlled atmospheric breakdown at a distance depends on both the compression and focusing of the laser beam, and also on the breakdown mechanism. For normal atmospheric constituents and available laser wavelengths, the ionization energy is much greater than the photon energy. If the laser pulse time is so short that avalanche breakdown cannot occur, multiphoton ionization becomes important. However, the more photons one needs, the more difficult it is to ionize. In this respect, ultraviolet photons are better than optical, which in turn are better than infrared. In this report, we examine multiphoton ionization via the excitation of an intermediate state. Most experimental data indicate that the ionization does occur through an intermediate state both for nanosecond (ns) and femtosecond (fs) pulses. This makes ionization easier to accomplish than it might otherwise have been and is thereby of potential importance to the ONR program. This report surveys some of the experimental data and also examines the theoretical basis for the frequent importance of multiphoton ionization via an intermediate state.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 30, 2003
- Accession Number
- ADA416228
Entities
People
- Wallace M. Manheimer
Organizations
- United States Naval Research Laboratory