Abstract
Abstract Structured illumination microscopy (SIM) is a well-established fluorescence imaging technique, which can increase spatial resolution by up to a factor of two. This article reports on a new way to extend the capabilities of structured illumination microscopy, by combining ideas from the fields of illumination engineering and nanophotonics. In this technique, plasmonic arrays of hexagonal symmetry are illuminated by two obliquely incident beams originating from a single laser. The resulting interference between the light grating and plasmonic grating creates a wide range of spatial frequencies above the microscope passband, while still preserving the spatial frequencies of regular SIM. To systematically investigate this technique and to contrast it with regular SIM and localized plasmon SIM, we implement a rigorous simulation procedure, which simulates the near-field illumination of the plasmonic grating and uses it in the subsequent forward imaging model. The inverse problem, of obtaining a super-resolution (SR) image from multiple low-resolution images, is solved using a numerical reconstruction algorithm while the obtained resolution is quantitatively assessed. The results point at the possibility of resolution enhancements beyond regular SIM, which rapidly vanishes with the height above the grating. In an initial experimental realization, the existence of the expected spatial frequencies is shown and the performance of compatible reconstruction approaches is compared. Finally, we discuss the obstacles of experimental implementations that would need to be overcome for artifact-free SR imaging.
Highlights
Super-resolution (SR) microscopy techniques are able to circumvent the Abbe–Rayleigh diffraction limit, enabling to resolve object features smaller than half the wavelength of light
We consider an extension of structured illumination microscopy (SIM), which is a widely popular fluorescence SR microscopy technique in which the sample is illuminated by a series of nonuniform light patterns, typically obtained by simple two-beam interference (Figure 1(a)), resulting in a lateral resolution improvement of up to a factor of two [1, 2]
Since contrary to DMSIM the illumination spatial frequency of DM-localized plasmon SIM (LPSIM) is not limited by the optical transfer function (OTF) of the illumination optics, the proposed technique has the potential to improve upon a higher initial numerical aperture (NA)
Summary
Super-resolution (SR) microscopy techniques are able to circumvent the Abbe–Rayleigh diffraction limit, enabling to resolve object features smaller than half the wavelength of light. SIM has undergone continuous advancements including resolution improvements above the initial twofold-resolution gain limit [9,10,11,12,13] The key to these improvements is that the moiré technique for downsampling high spatial frequencies into the passband of collection optics works if one is somehow able to offer illumination wave vectors killum higher than those that fit the far-field optics passband. A drawback is that this approach requires a nonlinear fluorophore response either through the use of high illumination intensities or special photoswitchable fluorescent labels, which limits its applicability in biological imaging [15, 16] Another compelling idea is to illuminate the sample not with simple pairs of plane waves but to combine several plane waves at once, to obtain an intensity pattern pumping the fluorophores that contains a multitude of difference wave vectors [17]. We discuss the illumination and reconstruction algorithm requirements to achieve optimal resolution enhancement
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