Share Email Print

Proceedings Paper

A new method to obtain narrowband emission from a broadband current using increased impedance of plasma-like media (Conference Presentation)
Author(s): Min Sup Hur; Bernhard Ersfeld; Adam Noble; Hyyong Suk; Dino A. Jaroszynski

Paper Abstract

In conventional radiation sources, narrowband radiation emission can be obtained by narrowband current oscillation. Usually the spectrum of the oscillating current is made narrow by a large or complicated structure for wave-particle interaction. One good example is the beam-undulator system. In this presentation, we introduce a new method to obtain a radiation emission with a well-collimated frequency without changing the broadband nature of a given current source. The method is based on our recent discovery of the new physical properties of the cut-off phenomenon, which broadly exists in general plasma-like media, such as plasma, waveguide, or photonic crystal, etc. A common feature of these media is the Bohm-Gross dispersion relation, which has a frequency condition to make the wavenumber zero. In the zero-wavenumber state, an electromagnetic wave cannot propagate through the medium, but instead, is reflected (i.e. cut-off). In regular steady-state analysis, the cut-off condition is characterized by infinite radiation impedance. An interesting question here is what would happen to the radiation power, if a non-zero current oscillating with the cut-off frequency were enforced in a medium (a current source, in contrast with the regular voltage source). A regular steady-state analysis for this situation leads to infinite power of radiation from Ohm’s law. We could solve such a paradoxical situation by analyzing the non-steady-state system; we found that the system can be described by a time-dependent Schroedinger equation with an external driving term. The solution of this equation shows a temporally growing electromagnetic field. When this concept is extended to a generally broadband current source, the spectral density at the cut-off frequency can be selectively enhanced (selectively enhanced emission, SEE). Hence a general broadband radiation source can be easily converted to a narrowband source by enclosing the system with a plasma-like medium. The current source seems to exist in many radiation systems with a low driver-to-emission efficiency. When the current is determined predominantly by the driver (for examples, laser pulses), while the feedback from the emitted field is weak, such current can be considered as a quasi-current source, We present a few examples (mostly from PIC simulations) to demonstrate the SEE; two-color-driven THz system enclosed by a tapered waveguide, THz emission from a magnetized plasma, and re-interpretation of experimental data. Those examples show that quasi-current source can be found in practical systems, and the SEE mechanism works.

Paper Details

Date Published: 21 June 2017
PDF: 1 pages
Proc. SPIE 10234, Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources II, 102340A (21 June 2017); doi: 10.1117/12.2265334
Show Author Affiliations
Min Sup Hur, Ulsan National Institute of Science and Technology (Korea, Republic of)
Bernhard Ersfeld, Univ. of Strathclyde (United Kingdom)
Scottish Univ. Physics Alliance (United Kingdom)
Adam Noble, Univ. of Strathclyde (United Kingdom)
Scottish Univ. Physics Alliance (United Kingdom)
Hyyong Suk, Gwangju Institute of Science and Technology (Korea, Republic of)
Dino A. Jaroszynski, Univ. of Strathclyde (United Kingdom)
Scottish Univ. Physics Alliance (United Kingdom)

Published in SPIE Proceedings Vol. 10234:
Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources II
Dino A. Jaroszynski, Editor(s)

© SPIE. Terms of Use
Back to Top
Sign in to read the full article
Create a free SPIE account to get access to
premium articles and original research
Forgot your username?