Electron Energy Distributions from High-Intensity Laser Interaction with Gases
Abstract
Recent advances in short-pulse high-intensity laser technology have enabled atomic physicists to explore new regimes in the interaction of light with matter. In the limit that the laser field strength dominates the Coulomb potential experienced by an electron in an atom, the description of the atom-field interaction by standard perturbation theory becomes inadequate. The interaction of high intensity lasers with atoms has been studied by theorists and experimentalists in the last few years (1). Experiments have focused on the interaction of low to moderate intensity (10 ^{12} W/cm^2 -10^{16} W/cm^2) lasers with low density gas samples (<10 ^{10}/cc). The resulting measurements (of free electron energies) has led to proposals that the interaction of high-intensity short-pulse lasers with gases could produce an x-ray laser pumped by rapid recombination of low energy electrons (2). The critical parameter determining the feasibility of such an x-ray laser is the free electron temperature resulting from the laser-gas interaction. This free electron temperature, however, has not been characterized under the high gas density (>10^{18 }/cc) conditions required for recombination lasers. Space charge forces associated with the high density nature of a plasma are expected to modify the electron energy distributions measured at low density. In this work we study the free electron energies resulting from interaction of high intensity lasers (10^ {16} W/cm^2-10 ^{18} W/cm^2) with high density gas samples (10^ {18}/cc-10^{19} /cc). We find that if the predicted electron temperature is not too high (or more precisely if we expect small thermal gradients) then the initial temperature can be predicted by a relatively simple model where an electron tunnels through a suppressed Coulomb barrier. If, however, the predicted temperature and associated thermal gradient is large, then the plasma will cool rapidly (by thermal conduction) to a temperature determined by the colder (low Z) regions at the plasma periphery.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1993
- Bibcode:
- 1993PhDT.......163G
- Keywords:
-
- LASERS;
- Physics: Atomic