"Generation of RF Radiation by Laser Pulse Trains in Air"

by Gavin Blair

Friday, November 11, 2022 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor Phillip Sprangle

We analyze and numerically simulate mechanisms for generating directed rf radiation by a low intensity laser pulse train (LPT) propagating into neutral air which undergoes ionization. Background levels of radioactivity play an important role in our model by initiating a collisional ionization process. A low intensity LPT photo-ionizes background negative ions (produced by ambient radioactivity) and provides the seed electrons necessary to initiate collisional ionization. The peak intensity associated with the LPT is far below tunneling ionization levels. The ponderomotive forces associated with the LPT oscillate the free electrons, predominately in the radial direction, for the parameters under consideration. The driven radial electron currents generate directed rf radiation. The spectrum of the rf radiation is found to consist of fundamental and harmonics associated with the pulse separation period. The intensity and angular distribution of the radiation is obtained using fluid equations which incorporate, among other things, the effects of background radioactivity, photo-ionization, collisional ionization, ponderomotive and space charge effects, and electron attachment/ recombination processes.

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