We demonstrate a single deep subwavelength slit for efficiently improving the excitation of surface plasmon polaritons (SPP) on metals through raising the dielectric permittivity of the output surrounding medium and numerically investigating their physical properties. Via adjusting the slit width and the output permittivity, either SPP launching intensity or its efficiency can be enhanced by almost 25 times and 170 %, respectively, compared with that under the symmetric surroundings. The underlying mechanisms are attributed to the spatial distribution change of the transmitted field and the plasmon density of state (DOS).

We numerically investigate the thermal radiation of one-dimensional deep subwavelength slits in the near infrared range. Using numerical calculations of single-slit and multi-slit structures, we find that high-level radiation efficiency can be achieved for a wide spectrum when ultra-thin intermediate layers are used, and it is less affected by structure parameters. The underlying mechanisms involve Surface Plasmon Polaritons resonance and Fabry-Perot interference at each slit and the interaction between adjacent slits. This structure helps understand and improve the design of thermal radiation control devices.