Plasmonic superfocusing of THz waves in metallic V-groove tapered waveguide theoretically considered by quasi-separation of variables

A non-adiabatic superfocusing theory of THz waves in a metallic V-groove tapered waveguide is studied by quasi-separation of variables for the explanation of our recent experimental results (Appl. Phys. Express, vol. 7, 112401, 2014). Approximate analytical solutions are obtained for the two regions at the apex and in the vicinity of it, where as the result the property of plasmonic superfocusing is analytically discussable in details.