Guideless Optical Sensing Using Space-Time Surface Plasmon Polaritons

Surface plasmon polaritons have been employed in a wide spectrum of sensing applications. However, as a surface plasmon polariton propagates along the surface of a metal-dielectric interface it rapidly diffracts and is absorbed reducing the sensitivity of a measurement. Attempts to prevent diffraction have included waveguides of many types but these require precise fabrication to mitigate dissipative losses. We propose using space-time surface plasmon polaritons for sensing. Our calculations show that proper selection of spatial frequency and temporal frequency correlations will produce a wave packet that propagates without diffraction or dispersion. This is possible without any waveguides or surface patterning.