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

M S Hur,H Suk,A Noble,B Ersfeld,D A Jaroszynski

doi:10.1038/srep40034

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.

Highlights

Intense, short-duration pulses of monochromatic electromagnetic radiation are very powerful tools for exploring and controlling the dynamics and structure of matter
When the J-source is immersed in a uniform cut-off region [Fig. 1c], the spectrum of the signal determined 10 μm from the J-source is enhanced by factor of 5 from case C, i.e. has an electric field intensity that is 25-fold larger than that obtained for emission in entirely free space and the bandwidth is even lower, 2.5 THz
We observe that selectively enhanced emission (SEE) is efficient with current sources

Summary

Introduction

Short-duration pulses of monochromatic electromagnetic radiation are very powerful tools for exploring and controlling the dynamics and structure of matter. We discover that a monochromatic, continuously oscillating current source in a cut-off region generates a temporally growing and spatially diffusing electric field, which is a solution of the driven-Schrödinger equation[9].

Results

Conclusion