Volume and surface mode coupling experiments in periodic surface structures for use in mm-THz high power radiation sources

Planar Periodic Surface Lattice (PSL) structures of different configurations have been designed, fabricated and measured in the 140-220 GHz frequency band. Surface mode resonances are observed in ‘mesh’ PSL structures. We establish that, when mounted on suitable metal-backed dielectric substrates, PSLs exhibit ‘mode-locked’ coherent cavity eigenmodes formed from coupled volume and surface modes. The ‘proof-of-principle’ coupling of volume and surface modes and concept of mode selection in a large cavity, which can lead to the innovation of high power mm-THz radiation sources, is demonstrated. Evidence of coupled eigenmode formation in a 0.64 mm planar PSL measured at 325-500 GHz is presented, verifying the scalability of this work. Excellent agreement between numerical modelling and experiment is reported.