Increased impedance near cut-off in plasma-like media leading to emission of high-power, narrow-bandwidth radiation

Hur, M. S. and Ersfeld, B. and Noble, A. and Suk, H. and Jaroszynski, D. A. (2017) Increased impedance near cut-off in plasma-like media leading to emission of high-power, narrow-bandwidth radiation. Scientific Reports, 7. pp. 1-9. 40034. ISSN 2045-2322 (https://doi.org/10.1038/srep40034)

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Abstract

Ultra-intense, narrow-bandwidth, electromagnetic pulses have become important tools for exploring the characteristics of matter. Modern tuneable high-power light sources, such as free-electron lasers and vacuum tubes, rely on bunching of relativistic or near-relativistic electrons in vacuum. Here we present a fundamentally different method for producing narrow-bandwidth radiation from a broad spectral bandwidth current source, which takes advantage of the inflated radiation impedance close to cut-off in a medium with a plasma-like permittivity. We find that by embedding a current source in this cut-off region, more than an order of magnitude enhancement of the radiation intensity is obtained compared with emission directly into free space. The method suggests a simple and general way to flexibly use broadband current sources to produce broad or narrow bandwidth pulses. As an example, we demonstrate, using particle-in-cell simulations, enhanced monochromatic emission of terahertz radiation using a two-colour pumped current source enclosed by a tapered waveguide.

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