Breaking the diffraction barrier outside of the optical near-field with bright, collimated light from nanometric apertures

Abstract

The optical diffraction limit has been the dominant barrier to achieving higher optical resolution in the fields of microscopy, photolithography, and optical data storage. We present here an approach toward imaging below the diffraction barrier. Through the exposure of photosensitive films placed a finite and known distance away from nanoscale, zero-mode apertures in thin metallic films, we show convincing, physical evidence that the propagating component of light emerging from these apertures shows a very strong degree of collimation well past the maximum extent of the near-field (0/4n-0/2n). Up to at least 2.5 wavelengths away from the apertures, the transmitted light exhibits subdiffraction limit irradiance patterns. These unexpected results are not explained by standard diffraction theory or nanohole-based ''beaming'' rationalizations. This method overcomes the diffraction barrier and makes super-resolution fluorescence imaging practical.fluorescence microscopy ͉ nanoholes ͉ subdiffraction limit ͉ subwavelength imaging ͉ super-resolution T he spatial resolution of an optical system operating outside of the optical near-field can given by the Rayleigh criterion (1),where is the wavelength of the emitted photons and NA is the numerical aperture of the system. This criterion says that two point sources can be ''just resolved'' when their separation is W. The 0.61 term arises from the superposition of two Fraunhofer diffraction patterns for circular apertures (Airy disks) such that the principle maximum of one of the patterns coincides with the first minimum of the other. This superposition of two sources at distance W results in an intensity distribution of two peaks with a valley between with a contrast ratio (ratio of peak to valley intensities) of 0.81.In an effort to circumvent this limit, a method was first proposed in which light is leaked through an aperture much smaller than the wavelength in an opaque screen (2). Because the light through such an aperture is known to diffract heavily and the power flux through such an aperture is evanescent, the aperture must be placed in the optical near-field of the probe. This method, practically realized, is called near-field scanning optical microscopy (NSOM) (3-5). Super-resolution (resolution values smaller than W, above) with NSOM has been demonstrated often. NSOM, however, suffers from the low photon flux through a zero-mode waveguide (6, 7) and the requirement of strict maintenance of surface-to-aperture distance within a few nanometers (8). Parallel probe NSOM approaches have been proposed and developed in which a plate with periodic perforations of zero-mode waveguides is placed on top of a sample in the optical near-field (9, 10).The behavior of light emitted from periodically perforated arrays of subwavelength apertures in metal films on mesoscopic length scales, between the length regime where light classically propagates (d Ͼ Ͼ ; the far-field) and the range where it displays evanescent properties (shorter than half of a wavelength; the near-field), is ...

DNA in nanochannels—directly visualizing genomic information

“…Another possibility is integrated sub-wavelength light sources that provide near-field optical imaging. 15,65…”

Effect of Nanohole Spacing on the Self-Imaging Phenomenon Created by the Three-Dimensional Propagation of Light through Periodic Nanohole Arrays

“…At values of z > 6 μm, the intensity of the transmitted radiation decreased and there is no appearance of a clear second image revival plane as predicted by traditional Talbot theory. Hence, it appears that the transmitted field is modulated in a striking manner along the z -axis . The intensity profiles demonstrate that these nanohole arrays can cause the propagating light to constructively and destructively interfere, creating “dark” and “light” zones that can extend to large distances along the propagation axis.…”

“…Hence it appears that the transmitted field is modulated in a striking manner along the z-axis. 40 The intensity profiles demonstrate that these nanohole arrays can cause the propagating light to constructively and destructively interfere creating “dark” and “light” zones that can extend to large distances along the propagation axis.…”

Laser precision engineering: from microfabrication to nanoprocessing

“…Hence, MLA is operating in an optical region between the near field and far field, resulting in an optical mesofield with the coexistence of evanescent wave and propagating wave. Recent research on bioimaging also demonstrated that the super-resolution can be achieved to overcome the optical diffraction limit in an optical mesofield [108]. However, the detailed physics is still not very clear.…”