Superresolution Imaging via Subwavelength Hole Resonances

This work presents a superresolution imaging approach by using subwavelength hole resonances. We employ a subwavelength structure in which an array of tiny holes are etched in a metallic slab with the neighboring distance $\ensuremath{\ell}$ that is smaller than half of the wavelength. By tuning the frequencies of the incident wave at resonant frequencies, the subwavelength structure generates strong illumination patterns that are able to probe both low and high spatial frequency components of the imaging sample sitting above the structure. The image of the sample is obtained by performing stable numerical reconstruction from the far-field measurement of the diffracted wave. It is demonstrated that a resolution of $\ensuremath{\ell}/2$ can be obtained for reconstructed images, thus one can achieve superresolution by arranging multiple holes within one wavelength. The proposed approach may find applications in microscopies as well as wave-based imaging such as electromagnetic and ultrasound imaging. It attains two advantages that are important for practical realization. It avoids the difficulty of controlling the distance between the probe and the sample surface with high precision. In addition, the numerical reconstructed images are very stable against noise by only using the low-frequency band of the far-field data in the numerical reconstruction.