Abstract
The resolution of conventional optical elements and systems has long been perceived to satisfy the classic Rayleigh criterion. 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. Superresolution imaging techniques, which are noncontact, far field and label free, are highly desirable but challenging to implement. 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. 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. This work may promote the wider adoption and application of optical superresolution across different wave types and application domains.
Highlights
Due 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]
Superoscillation focusing has been applied to improve the resolution of superresolution microscopy based on fluorescent labels
The focused waves within the field of view (FOV) only constitute a few percentage of the total incident energy and most of the optical energy goes into the sidebands surrounding the superoscillation spot
Summary
Optimization design methods The design of an SOL mainly relies on optimization algorithms, among which particle swarm algorithms[146] are the most commonly used. Based on PSWFs, an optimization-free approach was proposed to construct a superoscillation focal spot for a given optical field profile and FOV [−D/2, D/2], and the corresponding superoscillatory mask transmission function could be obtained by reverse propagation using the scalar angular spectrum method[50]. This approach can be extended to 2D cases for optimization of the superoscillatory point spread function (PSF) for far-field superresolution imaging[157] using circular prolate spheroidal wavefunctions (CPSWFs)[158].
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