Imaging the near field

Ramakrishna, S. Anantha; Pendry, J. B.; Wiltshire, M C K; Stewart, William

doi:10.1080/09500340308235215

Cited by 261 publications

(139 citation statements)

References 19 publications

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“…When the layer thickness is much smaller than the probing wavelength, an effective-medium approximation is commonly used to describe the permittivities along different directions, that is, e x , e y and e z (ref. 23). Although the term 'hyperlens' was applied to metamaterials with a hyperbolic dispersion relationship, that is, e x ¼ e y and e z taking different signs 15 , elliptically dispersive metamaterials can also be used to build a hyperlens as long as the coverage for lateral wave-vectors is large enough 24 .…”

Section: Physics Of the Hyperlensmentioning

confidence: 99%

Hyperlenses and metalenses for far-field super-resolution imaging

2012

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The resolution of conventional optical lens systems is always hampered by the diffraction limit. Recent developments in artificial metamaterials provide new avenues to build hyperlenses and metalenses that are able to image beyond the diffraction limit. Hyperlenses project super-resolution information to the far field through a magnification mechanism, whereas metalenses not only super-resolve subwavelength details but also enable optical Fourier transforms. Recently, there have been numerous designs for hyperlenses and metalenses, bringing fresh theoretical and experimental advances, though future directions and challenges remain to be overcome.O ptical microscopy has revolutionized many fields such as microelectronics, biology and medicine. However, the resolution of a conventional optical lens system is always limited by diffraction to about half the wavelength of light. This diffraction barrier arises from the fact that subwavelength information from an object is carried by high spatial-frequency evanescent waves, which only exist in the near field. To overcome this diffraction limit, pioneering work has been carried out, including near-field scanning microscopy 1 , as well as fluorescence-based imaging methods 2,3 . These scanning-or random sampling-based nonprojection techniques achieve super-resolving power by sacrificing imaging speed, making them uncompetitive for dynamic imaging.Lens-based projection imaging remains the best option for high-speed microscopy. Immersion techniques have been proposed to enhance resolution, but they are limited by the low refractive indices of natural materials 4 . Emerging within the last decade, the fields of plasmonics and metamaterials provide solutions for engineering extraordinary material properties not found in nature, such as negative index of refraction 5,6 or strongly anisotropic materials 7,8 . This has provided tremendous opportunities for novel lens designs with unprecedented resolution 9 . Initiated by Pendry's seminal concept of the perfect lens 10 , a number of superlenses were demonstrated with resolving powers beyond the diffraction limit [11][12][13][14][15][16][17] . The optical superlens first achieved sub-diffraction-limited resolution by enhancing evanescent waves through a slab of silver 11 . As the evanescent-field enhancement is enabled by surface plasmon excitation, the subwavelength image is typically limited to the near field of the metal slab. However, the hyperlens-a metamaterial-based lens-can send super-resolution images into the far field by introducing a magnification mechanism. This has been considered as one of the most promising candidates for practical applications since its first demonstration in 2007 (refs 13,14). Recently, various other metamaterial-based lenses, that is, metalenses, have also been developed with both

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Section: Physics Of the Hyperlensmentioning

confidence: 99%

Hyperlenses and metalenses for far-field super-resolution imaging

2012

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“…15,16 The propagation constant k V should be near flat over a large range in the transverse momentum k u , in both the Cartesian and the curvilinear representations of (u, V, w) (see Figure 1c). This condition can also be applied to the (V, w) plane to ensure ray-like propagation in all three dimensions.…”

mentioning

confidence: 97%

“…The unit cells in these EM composites can be considerably smaller than the wavelength to describe material properties as an effective homogeneous medium. 15,16 Metamaterials have shown extraordinary functionalities, such as negative refraction, 12,17 cloaking of arbitrary objects, 18,19 and hyperlens, [20][21][22] and may pave the way to controlling the diffraction and dispersion of light beams further.…”

mentioning

confidence: 99%

“…A uniaxial near-flat local dispersion (eq 3a,b) enables the confinement of the subwavelength beam profiles along both the u and w dimensions during propagation. Such an EM material response can be obtained, e.g., by an effective medium 15,20,21 composed of thin layers of alternating different materials (blue and white layers in the inset of Figure 2), which provide s′ u ) s′ w )…”

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confidence: 99%

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Ray Optics at a Deep-Subwavelength Scale: A Transformation Optics Approach

et al. 2008

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We present a transformation optics approach for molding the light flow at the deep-subwavelength scale, using metamaterials with uniquely designed dispersion. By conformal transformation of the electromagnetic space, we develop a methodology for realizing subwavelength ray optics with curved ray trajectories. This enables deep-subwavelength-scale beams to flow through two-or three-dimensional spaces.

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“…In most physical realizations, this is primarily set by the levels of dissipation and next by the intrinsic lengthscale of the structure of the metamaterial. Hence, although a perfect image would not be attainable, substantial sub-wavelength image resolution is possible [6,14,19].…”

Section: Introductionmentioning

confidence: 99%