Terahertz surface plasmons for subwavelength sensing and spectroscopy

At THz frequencies, certain semiconductors support confined surface plasmons (SPs). Here we show that THz surface plasmons can be utilized to overcome the diffraction limit when performing spectroscopy on very thin samples of analyte. We present measurements of SP propagation on an InSb surface overlayed with thin polymer dielectric films, and show that the SP on the InSb surface is considerably more sensitive to the polymer layers than a surface mode propagating on a polymer covered gold surface. Using a simple analytical approach, we are able to recover the dielectric constant of the polymer analyte from our measurements on a 500 nm polymer film.