Alexey K. Nikitin

A way to determine the permittivity of metallized surfaces at terahertz frequencies

A method for determining the dielectric permittivity of metal surfaces at terahertz (THz) frequencies has been suggested and tested. The method implies excitation of surface plasmons (SPs) on the sample surface and measurements of the SPs propagation length and field penetration depth in air. The technique was tested on evaporated gold with Novosibirsk free-electron laser at the wavelength of 130 μm. The method suggested paves the way for refractometry of metallized surfaces at THz frequencies.

Growth of terahertz surface plasmon propagation length due to thin-layer dielectric coating

Here we consider a longstanding problem: why terahertz (THz) surface plasmons (SPs) do not run so far as the Drude theory predicts. We experimentally demonstrated that the main cause for this paradox was a drastic rise in the SP radiative losses at THz frequencies, not violation of the theory. Analysis of SPs induced with the radiation of the Novosibirsk free electron laser (λ=130  μm) showed that a thin dielectric layer (≈λ/250) on a metal surface can reduce the losses substantially and hence enlarge the SP propagation length several times. Furthermore, it was found that there was an optimal layer thickness corresponding to the minimum total SP energy losses; the cause of this phenomenon is discussed.

Experimental investigations into capability of terahertz surface plasmons to bridge macroscopic air gaps.

Results of experimental and theoretical studies of the capability of terahertz surface plasmons (SPs) to cross macroscopic air gaps in a substrate (or between substrates) with admissible losses are presented. SPs were launched with quasi-cw free-electron laser radiation with 130 μm wavelength (λ). We managed to detect SPs passing across gaps as wide as 100 mm (or about 10(3)⋅λ), which is very promising for development of terahertz SP circuitry. The phenomenon was harnessed for splitting an SP beam into two new ones, guided by their own individual plane-surface substrates.