Frequency upshifting of electromagnetic radiation via an underdense relativistic ionization front

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7206902

Savage, R L

An underdense, relativistically propagating ionization front has been utilized to upshift the frequency of an impinging electromagnetic wave from 35 GHz to more than 173 GHz in a continuously tunable fashion. The source radiation interacted with the ionization front inside a metallic waveguide. The front, simply a moving boundary between ionized and neutral gas, was created as a short, intense pulse of ionizing laser radiation propagated through the gas-filled waveguide. In 1991, W.B. Mori showed theoretically that large upshifts are possible using underdense ionization fronts (underdense implies that the plasma density is lower than that required to reflect the source radiation), where the source wave is transmitted through the plasma/neutral boundary. The author has extrapolated Mori's analysis to interactions within a waveguide. He launched source radiation both along and opposite to the direction of propagation of the front. Because the group velocity of the source radiation inside the waveguide was only half that of the ionization front, both the counter- and co-propagating source radiation were overtaken and transmitted into the front. In agreement with the theoretical predictions, the co-propagating wave was upshifted to a higher frequency than the counter-propagating wave for a given plasma density, and both upshifts were proportional to the front's density. The duration of the upshifted counter-propagating wave initially increased with plasma density to more than 7 nsec and was less than 2 nsec at higher densities. However, the [open quotes]reflection[close quotes] of the counter-propagating wave was not conclusively resolved. This is a new technique for generating high-power, short-pulse, tunable radiation, and has potential applications in areas such as time-resolved microwave spectroscopy, plasma diagnostics, and remote sensing.

• Research Organization: California Univ., Los Angeles, CA (United States)
• OSTI ID: 7206902
• Country of Publication: United States
• Language: English

Related Subjects

661300* -- Other Aspects of Physical Science-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BEAM-PLASMA SYSTEMS
ELECTROMAGNETIC RADIATION
RADIATIONS
SPECTRAL SHIFT
TUNING