Abstract
The fundamental properties of a wave precludes it from being localized to subwavelength distances in all dimensions of the wave's existence. The inability to focus electromagnetic waves to an all-direction subwavelength spot limits the 3D resolution of a conventional imaging system to about half the imaging wavelength. A plethora of super-resolution imaging systems have been designed which obtain super-resolution in one or two (but not all) dimensions, but they suffer various restrictions in working distance and the classes of objects they can image. In this paper, we report a first investigation into a wave that is focused to subwavelength dimensions in all directions. After reviewing the physics of wave dispersion and diffraction which seemingly preclude this phenomenon, we sidestep these preclusions using a broadband superoscillation waveform and synthesize an all-direction subwavelength focus. We report the salient spatial and temporal features of this wave, and apply it to achieve 3D super-resolution imaging.
Highlights
Can one focus a waveform to subwavelength dimensions in all directions? The very nature of a wave seems to preclude its subwavelength localization in all its directions of existence
In the field of electromagnetics, the inability to focus electromagnetic waves into a subwavelength spot leads to a fundamental resolution limit on classical imaging systems [1,2,3]
This work has reported the construction of an electromagnetic wave which is focused to a subwavelength spot in all directions
Summary
Can one focus a waveform to subwavelength dimensions in all directions? The very nature of a wave seems to preclude its subwavelength localization in all its directions of existence. Whereas it was long accepted that the diffraction limit precludes one from forming such images with a resolution beyond half the imaging wavelength, a plethora of super-resolution devices have been proposed, which sidestep the diffraction limit by involving and making clever use of evanescent waves [4,5,6,7,8,9,10,11]. These devices achieve super-resolution on the image plane by generating waveforms which decay exponentially in the longitudinal direction. A way to focus electromagnetic and acoustic waves to subwavelength dimensions in all directions would provide a direct path to super-resolution 3D imaging, with immediate applications in microscopy and many medical imaging modalities involving electromagnetic and ultrasound waves
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