The Application of Laser Saturation to the Efficient Generation of Short WaveLength Radiation from Plasmas.

Abstract

Abstract : Resonant laser pumping of transitions within atoms or ions represents a powerful mode of coupling laser energy into a gas or plasma. In the case of laser saturation of a resonance transition rapid heating of the free electrons by superelastic collision quenching of the laser pumped state has been shown to play the central role in this process. We have developed a computer code that models this laser ionization based on resonance saturation (LIBORS) and permits us to map the three dimensional nature of this complex interaction. We have been able to show by comparison with experiment that this LIBORS computer code can predict the radial and axial electron density and temperature profiles of the plasma formed along the path of the laser pulse. These experimental results in themselves represent the first detailed measurements of a sodium plasma created by laser resonance saturation and reveal the importance of laser attenuation in the formation of the plasma. We have also shown that both one and two photon resonant laser pumping of a cold, unexcited plasma created by two photon ionization of strontium vapor can lead to rapid excitation of high lying states of the strontium ion. Lastly, we have demonstrated parametric generation within this same strontium plasma when the laser is tuned close to a two photon transition of the ion.