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Two-dimensional dispersion relation for (a) type I hyperbolic metamaterial (dielectric permittivity tensor components being ε|| = 0.36, ε⊥ = −13.31) and (b) type II hyperbolic metamaterial (ε|| = −1.06, ε⊥ = 8.09) The insets schematically show the direction of the group velocity for waves in certain parts of the k-space; for the type I hyperbolic meta-material, it is possible that the majority of lower-k waves propagate in the y-direction (the canalization regime). Only one branch for k⊥ is shown in the lossy case to aid the visual comparison with the lossless case.
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We propose a device for subwavelength optical imaging based on a metal-dielectric multilayer hyperlens designed in such a way that only large-wavevector (evanescent) waves are transmitted while all propagating (small-wavevector) waves from the object area are blocked by the hyper-lens. We numerically demonstrate that as the result of such filtering...
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... These exceptions allow the signal field to be differentiated from the background field due to its unique spectral characteristics [20]. Alternatively, one can design a specialized illumination and imaging system that separates the signal light field from the background within a specific spatial area, similar to the approach used in dark-field microscopy [21]. Direct measurement in optical microscopy offers significant advantages, as it avoids chemical contamination from fluorescence labeling and eliminates strict requirements on material selection and excitation conditions. ...
The resolution of an optical microscope is determined by the overall point spread function of the system. When examining structures significantly smaller than the wavelength of light, the contribution of the background or surrounding environment can profoundly affect the point spread function. This research delves into the impact of reflective planar substrate structures on the system’s resolution. We establish a comprehensive forward imaging model for a reflection-type confocal laser scanning optical microscope, incorporating vector field manipulation to image densely packed nanoparticle clusters. Both theoretical and experimental findings indicate that the substrate causes an interference effect between the background field and the scattered field from the nanoparticles, markedly enhancing the overall spatial resolution. The integration of vector field manipulation with an interferometric scattering approach results in superior spatial resolution for imaging isolated particles and densely distributed nanoscale particle clusters even with deep subwavelength gaps as small as 20 nm between them. However, the method still struggles to resolve nanoparticles positioned directly next to each other without any gap, necessitating further work to enhance the resolving ability. This may involve techniques like deconvolution or machine learning-based post-processing methods.
... The approaches could be generally categorized into near-field and far-field ones. The near-field modalities, such as near field scanning optical microscopy (NSOM) [ 6 , 7 ], photon scanning tunneling microscope (PSTM) [8] , superlens [ 9 , 10 ] and hyperlens [11] , capture the evanescent waves to reach a nanoscale resolution. However, these modalities require a probe or photosensitive material to be in close proximity to the objects, causing severe difficulties in imaging subsurface objects and thus leading to substantial technological challenges in practical applications. ...
Due to the diffraction properties of light waves, optical microscopy suffers from a fundamentally limited resolution of ∼ /2, where relates to the illumination wavelength. Though near-field methods capturing the evanescent waves can reach a resolution of several nanometers, the extremely short working distance has restrained their applications. Typical far-field super-resolution microscopies using fluorescence to monitor the labelled samples also have their limitations in applications because of their phototoxicity and complex preprocessing. We hereby proposed a label-free super-resolution microscopy based on non-diffraction superoscillation beam (NDSB) illumination. We developed a transmission-mode confocal optical microscopy and experimentally demonstrated an imaging resolution of 0.285 at the illumination wavelength of 632.8 nm. As NDSB owns the capabilities of self-healing and deep penetration in dense media, we could clearly visualize the fine complex structures while NDSB illuminated from the backside of a 175-μm-thick glass substrate. As a result of NDSB's excellent penetration and superoscillatory transverse size, the 3D super-resolution capability of the proposed microscopy was experimentally verified. Owing to the advantages of label-free imaging, far field, super resolution, self-healing behaviour and deep penetration, we believe the proposed NDSB microscopy bears the potential to become a promising tool for 3D super-resolution visualization in both biological and nonbiological samples.
... Typically, type I HMMs with transverse effective permittivity of marginally above zero and axial effective permittivity of significantly below zero yield a nearly flat isofrequency surface, therefore, all waves propagate in the radial directions within the hyperlens. This condition called the 'canalization regime' is nearly a must for optimal hyperlens performance [4,5]. Cylindrical [6][7][8] and spherical hyperlenses [9] with alternating dielectric/metal layers have been portrayed as efficient experimental platforms for one-and two-dimensional super-resolution imaging, respectively. ...
Hyperlenses offer an appealing opportunity to unlock bioimaging beyond the diffraction limit with conventional optics. Mapping hidden nanoscale spatiotemporal heterogeneities of lipid interactions in live cell membrane structures has been accessible only using optical super-resolution techniques. Here, we employ a spherical gold/silicon multilayered hyperlens that enables sub-diffraction fluorescence correlation spectroscopy at 635 nm excitation wavelength. The proposed hyperlens enables nanoscale focusing of a Gaussian diffraction-limited beam below 40 nm. Despite the pronounced propagation losses, we quantify energy localization in the hyperlens inner surface to determine fluorescence correlation spectroscopy (FCS) feasibility depending on hyperlens resolution and sub-diffraction field of view. We simulate the diffusion FCS correlation function and demonstrate the reduction of diffusion time of fluorescent molecules up to nearly 2 orders of magnitude as compared to free space excitation. We show that the hyperlens can effectively distinguish nanoscale transient trapping sites in simulated 2D lipid diffusion in cell membranes. Altogether, versatile and fabricable hyperlens platforms display pertinent applicability for the enhanced spatiotemporal resolution to reveal nanoscale biological dynamics of single molecules.
... Furthermore, multilayered structures are also relatively stable and resilient to changes of the environmental conditions, which is especially important to build imaging platform with better uniformity and lower distortions in the far field. Multilayer hyperbolic metamaterials have been investigated in the UV and visible bands for imaging applications such as nanolithography [34], dark-field hyperlens [35,36] and photoluminescence enhancement [37]. For example, Liu et al. achieved 1.8x sub-diffraction demagnification imaging lithography at 365 nm using Ag/SiO 2 hyperlens and introduced the plasmonic reflector layer to improve imaging contrast. ...
The diffraction limit of light due to the loss of evanescent waves that carry high spatial frequency information in the far field restricts the practical applications of terahertz imaging technology. In order to break the diffraction limit, we investigate the super-resolution capability of different types of multilayered graphene-dielectric hyperbolic metamaterials. A super-resolution of λ/10 is achieved for both the cylindrical and planar structures. A prominent advantage of graphene-dielectric hyperbolic structures is the dynamic tunability of the dispersion and super-resolution performance by adjusting the chemical potential of graphene through conveniently changing the gate voltage without modifying the geometry of the hyperbolic structures. Furthermore, we have investigated the influence of bilayer thickness variations on the super-resolution performance. Finally, we apply the planar hyperbolic structures for the super-resolution imaging and a roughly five-fold lateral resolution enhancement is realized in our approach. Due to many prominent advantages including super-resolution over broad spectral range, dynamic tunability, good stability and robustness, we believe this work could contribute to the improvement of the resolutions of terahertz imaging systems and the development of hyperbolic metamaterial modulation devices in the terahertz band.
... Numerous efforts have been devoted to develop principles, designs, and materials for nanoimaging devices in various applications [2][3][4][5]. Inspired by the pioneer work of Zubin Jacob [6], a separate branch of nanoimaging research abounds with studies of electromagnetics in hyperbolic metamaterials [7][8][9][10][11][12][13]. In addition to the general nanoimaging studies in the proposed hyperbolic metamaterial, special attention has been given to broadband supported high-k (i.e., wave vector) hyperbolic polaritons [14][15][16][17][18]. ...
A novel strategy to broadband nanoimaging of microworld in the near field is reported by using a folded-geometry transformation. This approach relies exclusively on hyperbolic metamaterials with engineered anomalous hyperbolic dispersion. The restriction on the signs of gradient in the dispersion enables invariable propagation angle of hyperbolic polaritons at different wavelengths, which could be utilized to dramatically broaden the bandwidth. Interestingly, a pseudo-broadband nanoimaging based on hyperbolic metamaterial consisting of alternating metal (e.g. Ag) and plasmonic nanocomposite (e.g. Au-Al2O3) layers is demonstrated. Such strategy of transformation optics-based broadband nanoimaging allows for a new class of robustly manufacturable nanophotonic systems, although additional gain-assisted compensation is needed to improve the performance of nanoimaging.
... The scattering waves generated by the fine details of defects are mainly represented by evanescent waves [18][19][20]. This key information is easily overwhelmed by the strong background illumination which mainly consists of low-k spatial components (or propagating waves) [21]. However, in most imaging methods, the propagating waves play a dominant role for image construction, leading to the low-contrast results. ...
Terahertz imaging has recently attracted great attention owing to the abilities of high penetration and low ionizing damages. However, the low resolution and low contrast resulting from the diffraction limit and unwanted background illumination significantly hinder the extensive usage. In this Letter, we propose and numerically demonstrate a terahertz subwavelength imaging method capable of extracting only the edges and fine features of the targets. The underlying physics is the efficient transmission of the scattering evanescent waves related to key geometric information while blocking the propagating components. By exploiting the structurally induced plasmons in a bounded metallic waveguide, the transmission channel for evanescent waves is realized by hyperbolic metamaterials through periodically stacking dielectric layers. On this basis, high-contrast edge detection with a resolution up to ${0.1}\lambda$ 0.1 λ is demonstrated at terahertz wavelengths. The proposed terahertz imaging method may find important applications in non-destructive testing, weak scattering object detection, and high-contrast microscopy.
... Equations (13) and (14) can also be used to explain why darkfield imaging [86][87][88] improves the contrast. Blocking the low spatial frequencies reduces the power contained in the signal, hence the flat variance in the Fourier spectrum. ...
... It rather aims to selectively amplify the high spatial frequencies buried under the noise without excessive noise amplification. Therefore, it does not sacrifice brightness or strongly enhance artifacts unlike dark-field imaging [87]. The theory presented here can also be applied to bright field imaging. ...
Recently an optical amplification process called the plasmon injection scheme was introduced as an effective solution to overcoming losses in metamaterials. Implementations with near-field imaging applications have indicated substantial performance enhancements even in the presence of noise. This powerful and versatile compensation technique, which has since been renamed to a more generalized active convolved illumination, offers new possibilities of improving the performance of many previously conceived metamaterial-based devices and conventional imaging systems. In this work, we present, to the best of our knowledge, the first comprehensive mathematical breakdown of active convolved illumination for coherent imaging. Our analysis highlights the distinctive features of active convolved illumination, such as selective spectral amplification and correlations, and provides a rigorous understanding of the loss compensation process. These features are achieved by an auxiliary source coherently superimposed with the object field. The auxiliary source is designed to have three important properties. First, it is correlated with the object field. Second, it is defined over a finite spectral bandwidth. Third, it is amplified over that selected bandwidth. We derive the variance for the image spectrum and show that utilizing the auxiliary source with the above properties can significantly improve the spectral signal-to-noise ratio and resolution limit. Besides enhanced superresolution imaging, the theory can be potentially generalized to the compensation of information or photon loss in a wide variety of coherent and incoherent linear systems including those, for example, in atmospheric imaging, time-domain spectroscopy, ${\cal P}{\cal T}$ P T symmetric non-Hermitian photonics, and even quantum computing.
... When ε ⊥ and ε are of opposite signs, which can be satisfied in optical wavelengths with noble metals such as gold or silver (Ag), the medium has a hyperbolic dispersion relation and is called a hyperbolic medium. The hyperbolic dispersion is known as Type I if ε ⊥ < 0 and ε > 0 and Type II if ε ⊥ > 0 and ε < 0 [29]. In the hyperbolic medium of Type II, only the waves with large transverse wavenumbers can propagate, but in the hyperbolic medium of Type I, any waves with arbitrary transverse wavenumbers can travel along the optical axis. ...
Planar-ports hyperlens structures made of two or four cascaded triangular cuts of planar periodic structures are presented. The hyperlenses are capable of converting electromagnetic evanescent fields to propagating waves, featuring subwavelength resolution and image magnification. One of the two proposed structures features parallel input and output ports. The proposed structures improve the phase and amplitude unbalances, magnification, and resolution of previous planar hyperlenses. Compared to several previous cylindrical hyperlens structures, the proposed structures show competitive or better features. One of the best designs of the proposed structures offers a magnification of 3.86, a resolution of 45 nm, $\lambda /{8}$ λ / 8 at the free space wavelength of 365 nm, optical modulation, a measure of image contrast of 0.286, and amplitude unbalance, a measure of image quality of 0.08, the smallest among all previous structures. Detailed comparative data of performance are provided. Although the magnification of the proposed planar structures is somewhat smaller than some of the previous cylindrical ones, the performance of the proposed hyperlenses is better or competitive with respect to resolution and image quality.
... Sub-diffraction objects are resolved by the hyperlens in the far-field image. background illumination, a dark-field hyperlens that adopts type II HMM (ε eff o < 0 and ε eff e > 0) was proposed [90,91]. The dark-field hyperlenses are also made of metal-dielectric multilayers operating in the type II regime, as illustrated in Fig. 8(a). ...
A hyperbolic material (HM) is an optical material that exhibits a unique property of having anisotropy with simultaneously different signs of the permittivity tensor components. Such a property leads to novel optical phenomena. HM can host highly localized bulk plasmon polaritons and directional surface waves with the large wavevectors required in various applications in nano-guiding, sensing, and imaging. Research on HMs has been intensified in the last decade thanks to progress in nanofabrication and advances with two-dimensional materials. This paper reviews the recent developments in novel structures and materials with hyperbolic materials such as metasurfaces, hypercrystals, waveguides, and cavities. Furthermore, various applications that take advantage of the unique optical phenomena of HMs are covered, including negative refraction and photonic spin Hall effect for optical signal sorting, super-resolution, refractive index sensing, and mid-infrared vibrational spectroscopy.
... A hyperlens made of the material with an indefinite permittivity tensor (so-called hyperbolic metamaterial [2,3]) was shown to beat the diffraction limit [4]. A dielectric-type hyperbolic metamaterial can be used for fabrication of bright-field hyperlenses [5,6], while the metallic-type one can be exploited for dark-field microscopy [7,8]. Metamaterial flat lenses [9,10] and metasurfaces [11][12][13] have been proposed for subwavelength imaging as well. ...
Superresolution is an important feature needed for modern optical microscopy. It can be achieved by using the transmission of evanescent waves in hyperbolic metamaterials. However, such devices suffer from material losses. Here we investigate a recently proposed metamaterial solid immersion lens—an assembly of dielectric nanoparticles. Using the multiple-scattering theory we reveal conversion of evanescent to propagating waves under conditions of coherent scattering. However, efficiency of the conversion is rather low as confirmed by the transmission of the fields of a couple of point sources. Comparing the scattering of light of a spherical cluster of nanospheres with that of a solid sphere of the same radius we find the same far fields in both cases. Generally, our conclusion is that material in the form of the assembly of nanoparticles behaves like an effective medium and does not demonstrate the superresolution in the far field. We believe that the resolution of the metamaterial solid immersion lens has the same origin as that of the conventional sold immersion lens.
