DocumentCode :
1629321
Title :
Dipole RF Power from Laser Plasmas with no Dipole Moment
Author :
Felber, Franklin
Author_Institution :
Starmark, Inc., San Diego
fYear :
2007
Firstpage :
779
Lastpage :
779
Abstract :
Summary form only given. The radio-frequency power radiated from certain laser-target plasmas in a vacuum can be orders of magnitude greater than expected from such sources that have a negligible electric dipole moment. A model combining the Tidman-Stamper circuit model of a laser-target plasma with the theory of radiation from currents immersed in plasmas, however, predicts scaling of electric-dipole power radiated from laser plasmas in agreement with experiments. The model estimates the power, angular distribution, and spectrum of radio-frequency (rf) radiation from laser plasmas produced on solid surfaces in vacuum. The estimates of rf power are compared with experimental data from CO2-laser interactions with copper targets at incident intensities from about 60 MW/cm2 to 40 GW/cm2. The model agrees with the limited observations of rf-power scaling with laser power, with the radial and angular dependence of the near-zone fields, and with the correspondence of rf radiation with the formation of a critical-density surface. The model should be valid over a range of laser wavelengths from the ultraviolet to the long- wavelength infrared. The model should also be valid over a range of incident laser intensities that produce plasma electron temperatures of a few eV, just above the plasma ignition threshold, to 1 keV or higher. The laser spot size and pulse duration are key parameters affecting the rf power. The theory suggests that electromagnetic radiation does not escape from the electron current immersed in the plasma plume, which is overdense to rf radiation. But the return current, which flows in the diffuse plasma surrounding the plume, does radiate as a dipole. If a current ring that has zero dipole moment is partly shielded, the unshielded part will radiate dipole power. The net effect is that the poloidal electron current in certain laser plasmas radiates as an electric dipole, instead of a quadrupole.
Keywords :
electric moments; plasma collision processes; plasma production by laser; plasma temperature; Tidman- Stamper circuit model; critical density surface; dipole radiation; dipole rf power; electric dipole moment; electric-dipole power radiation; electron return current; inductive overdense plasma voltage; laser plasmas; plasma electron temperature; plasma ignition threshold; plasma immersed currents; radiofrequency power radiation; radiofrequency radiation angular distribution; radiofrequency radiation power; radiofrequency radiation spectrum; resistive overdense plasma voltage; vacuum laser-target plasmas; zero current ring dipole moment; Electrons; Laser modes; Laser theory; Plasma sources; Plasma temperature; Plasma waves; Power lasers; Predictive models; Radio frequency; Surface emitting lasers;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Plasma Science, 2007. ICOPS 2007. IEEE 34th International Conference on
Conference_Location :
Albuquerque, NM
ISSN :
0730-9244
Print_ISBN :
978-1-4244-0915-0
Type :
conf
DOI :
10.1109/PPPS.2007.4346085
Filename :
4346085
Link To Document :
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