Abstract
Planar periodic surface lattice (PSL) structures based on thin, subwavelength substrates have been studied experimentally and numerically. Coupled eigenmode resonances composed of partial volume and surface modes are observed for PSLs with lattice periodicities of 1.50 mm and 1.62 mm etched onto thin copper-backed, substrates. We show that the copper backing is essential for mode-selection in a multi-moded structure and demonstrate good agreement between the experimental results and coupled dispersion plots calculated using CST Microwave Studio. For the first time, evidence of a coupled eigenmode in a metadielectric PSL is presented. It is shown that metadielectric PSLs can support coupled resonances over a narrow bandwidth and are relevant to the innovation of tunable filters, absorbers and sources. Concepts discussed in this work are valid across the frequency spectrum from optical to THz and mm-wave frequencies and are fundamental to the innovation of novel mm-wave–THz sources as well as highly efficient solar cells, diagnostic instruments and antennae.
Highlights
Efficient, high power millimetre and terahertz radiation sources are highly sought after for their diverse and farreaching applications in optics, imaging [1,2,3] and security [4], communications [4,5,6] medical technology, particle acceleration [7, 8] spectroscopy [9,10,11] and scientific research [12,13,14,15]
We have shown the resonant coupling of volume and surface modes leading to the formation of well-defined coupled eigenmodes and demonstrating the principle of mode selection in multi-moded structures, with applications in novel radiation sources based on different gain media
Mode coupling was found to be most effective in the dz= 1.50 mm and dz= 1.62 mm periodic surface lattice (PSL) structures, while lower signal to noise ratios and Fabry–Perot resonances were prevalent in PSLs with larger periodicities
Summary
High power millimetre and terahertz radiation sources are highly sought after for their diverse and farreaching applications in optics, imaging [1,2,3] and security [4], communications [4,5,6] medical technology, particle acceleration [7, 8] spectroscopy [9,10,11] and scientific research [12,13,14,15]. One method of overcoming this challenge is through the use of two-dimensional periodic surface lattice (PSL) structures, which have been successfully incorporated into high power microwave sources for a number of years [15,16,17,18,19] and enable mode rarefaction in a multi-moded structure. Higher output powers at mm-wave and THz frequencies, are achieved by coupling volume and surface modes to enable mode selection in an oversized cavity, providing single-mode excitation at high frequencies without compromising the power output [20, 21]. This work explores the fundamental volume and surface field coupling and determines the necessary criteria and optimum conditions for coupled eigenmode formation to better control the transverse modes and enable interaction with an electron beam in an oversized cylindrical interaction space. Conversion between the cylindrical and planar systems can be achieved via conformal mapping
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