ISSTT Proceedings

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Tunable High Frequency Radiation Source Utilizing a Relativistically Propagating Ionization Front

Authors:
R.L. Savage, Jr., C. Joshi, W.B. Mori
Abstract:
We have experimentally demonstrated a new type of tunable, high power radiation source capable of producing very short pulses. This technique utilizes a laser-produced ionization front which passes through a pulse of microwave radiation and in doing so causes the frequency of the radiation to upshift dramatically. By controlling the density of the plasma in the ionization front, we can continuously vary the degree of upshift. Source radiation at 35 GHz has been upshifted to more than 116 GHz. The source radiation is provided by a pulsed magnetron that gives 300 nsec long, 10 kW peak power pulses at 35 GHz. This radiation is fed via rectangular waveguide through the side wall of a cylindrical copper cylinder that is closed by quartz windows at each end. The TE01 mode is excited and resonates in the cavity which is evacuated and filled with azulene vapor, which is chosen because it is easily ionized by ultraviolet radiation. A short (50 psec), intense (40 mJ) ultraviolet (266 nm) laser pulse is introduced through one of the quartz windows and propagates down the axis of the cavity. As the laser ionizes the azulene vapor, a sharp boundary is formed between the neutral gas and the newly created plasma. It is this boundary, which propagates at the group velocity of the laser radiation in the plasma-filled guide, that we refer to as an ionization front.
Categories:
Circuits, Miscellaneous
Year:
1991
Session:
9
Full-text:
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Page Number(s):
585-596