![]() ![]() Dielectric microspheres on sample surfaces can also yield subdiffraction features of the sample in the form of magnified virtual images, which can then be captured with a conventional optical microscope 4, 5, by relying on the conversion of evanescent waves into propagation waves. ![]() Near-field optical-scanning microscopes 3 exploit this property to achieve subdiffraction resolution of tens of nanometres using a nano-optical probe. To overcome this restriction, retrieving higher frequency components from evanescent waves, which exist near the objective surface within a distance of less than one wavelength, is necessary. The absence of higher frequency components results in limited optical resolution. For optical waves with a wavelength of λ, in a homogeneous lossless medium with refractive index n, the propagation of light acts as a band-limited linear space-invariant system 2 that filters out all components for which the spatial frequency exceeds n/λ within a distance of several wavelengths. Similar content being viewed by othersĭue to the propagation property of electromagnetic waves, the optical resolution of conventional optical systems is restricted to a basic theoretical limit of 0.61λ/NA (NA is the numerical aperture of the optical system) 1. This work may promote the wider adoption and application of optical superresolution across different wave types and application domains. This paper reviews recent developments in optical superoscillation technologies, design approaches, methods of characterizing superoscillatory optical fields, and applications in noncontact, far-field and label-free superresolution microscopy. The concept of superoscillation offers an alternative route to optical superresolution and enables the engineering of focal spots and point-spread functions of arbitrarily small size without theoretical limitations. Superresolution imaging techniques, which are noncontact, far field and label free, are highly desirable but challenging to implement. Paramount efforts have been made to develop different types of superresolution techniques to achieve optical resolution down to several nanometres, such as by using evanescent waves, fluorescence labelling, and postprocessing. The resolution of conventional optical elements and systems has long been perceived to satisfy the classic Rayleigh criterion.
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