Multiphoton Ionization for the Production of X-Ray Laser Plasmas

Abstract

In the long wavelength (or high intensity) limit, above threshold ionization (ATI) is primarily the result of the interaction of a newly freed electron with the laser field. A classical model of ATI predicts that the energy of a newly released electron can be controlled by varying the laser wavelength and polarization. Similar predictions are made by Keldysh-style theories. Measurements, performed using both linearly and circularly polarized picosecond 10 μm pulses, confirm these conclusions. Cold, high-Z plasmas for recombination XUV lasers can be produced by multiphoton ionization with linearly polarized visible or UV radiation. Hot electrons, potentially suitable for electron-pumping of ionization-phase XUV lasers can be produced using longer wavelength or circularly polarized light.