The investigation of the subwavelength focusing spot resulting from modified surface plasmon wave at planar interface

Abstract

This paper proposes a technique of realizing sub-wavelength focusing spot on surface by modifying the spatial phase in far-field. This focusing spot will use to detect the spectrum of the monolayer biomolecules on the planar surface. Taking the advantage of modifying spatial phase and polarization of incident laser beam, the field distribution in near-field (near focal point) can be changed and can achieve to the smallest spot size of sub-wavelength under the reasonable adjustment of the phase and polarization of incident beam in far-field. Although nano-scale light sources can produce by labelling dye on nanoparticles, quantum dots etc., but technically it is not easy to finely manipulate nanoparticles. On the contrary, using the planar thin film of matured, reliable fabrication processes, not only the near-field twisted electromagnetic of nanostructure can be eliminated, but also fixing the biomolecules on planar surface makes its arrangement to have the consistent direction, thereupon the overall behavior of molecular vibration is simple, pure, and advantageous to detect the vibrational spectra of the monolayer molecules on surface.