Russian Federation 7 baburin@bmstu.ru 8 melentiev@isan.troitsk.ru 9 balykin@isan.troitsk.ru * A.S. Baburin and A.S. Kalmykov are contributed equally to this work.Abstract: We demonstrate the optical medium for surface plasmon -polariton waves (SPP) propagation with ultra low losses corresponding to the theoretically limited values. The unique element of the optical medium is an atomically-flat single-crystalline silver thin film which provides extremely low losses. The SPP excited on the surface of such thin films (λ = 780 nm) is characterized by a SPP propagation length equal to 200 µm, which is twice longer than previously reported experimental results and corresponds to theoretically limited values for silver films.
Due to losses in metals, the propagation length of the surface plasmon-polariton (SPP) waves on metal surfaces is small. This severely limits development of numerous applications of the SPP optics: in the near-infrared spectral region propagation length of SPP waves is no longer than 200 μm as for plane SPP waves and for all types of SPP waveguides. In this work, we show that the focusing of SPPs allows for the first time realizing open-type waveguide for SPP waves characterized by long distance of SPP effective propagation length up to 1 mm at a wavelength of 780 nm. We show that focused SPP waves in such a waveguide can be effectively excited by a 16 fs laser as well as be amplitude modulated within a bandwidth about 3.5 THz. The fast dynamics of the focused SPP waves is limited by the SPP group velocity dispersion. The large effective propagation length of the SPPs and its ultrahigh bandwidth open up new possibilities for using focused SPPs in different areas of plasmonics and photonics.
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