Splitting a terahertz surface plasmon polariton beam using Kapton film

It has been experimentally shown that a rigid polyimide Kapton film of submillimeter thickness is sufficiently transparent in the frequency range of 1.2–3 THz and can be used for splitting surface plasmon polaritons (SPPs) propagating along a flat conducting surface. The transmittance T and reflectance R measured for SPPs excited by a free-electron laser radiation ( λ = 130 µ m ) in “gold–ZnS layer–air” flat structures are in good agreement with the results of numerical simulations obtained using the rigorous coupled-wave analysis technique. Transmittance of the SPPs decreases slightly when the layer gets thicker. To minimize the SPP radiative losses emerging due to diffraction of the SPPs on the impedance discontinuity, the Kapton film should be placed normal to the guiding surface and brought in good contact with it (the gap must be less than λ / 2 ). The performed experiments clearly demonstrated Kapton films to be very promising for SPP beam splitting in large-scale terahertz SPP devices.