Vol. 43, Issue 2, pp. 383-392 (2013)

Abstract

Using the Green function method, we theoretically achieve good focusing beyond the diffraction limit in a visible light region through a subwavelength slit flanked by grooves. The full width at half maximum (FWHM) of the focused spot reaches 0.3λ (λ is the wavelength of incident light), which is far beyond the diffraction limited line width of 0.5λ. The phenomena of the exceeding diffraction limit in our structure exist in the range from 500 to 630 nm. Our results can be well explained by the interference interaction between the field of the central slit and the fields penetrating through the grooves. Such image focusing will give rise to various applications in near field microscopy, lithography, high-resolution image and help to improve the design of plasmonic nanodevices.