Final Report Summary - MAGPLASIMAG (Developing reconfigurable sub-diffraction-imaging devices using magnetized plasma)
The goal of this project is twofold: to employ magnetized plasma for achieving dynamically reconfigurable super-imaging at terahertz frequencies, and to develop various novel optical devices based on functional metasurfaces and metamaterials. The proposed sub-diffraction imaging using magnetized plasma does not involve complex and time consuming fabrication, it opens a new gate towards cost effective, facile and flexible superimaging devices.
Imaging lies in the heart of many important applications in biology, medical sciences, security, and semiconductor industries. Conventional imaging methods are limited by the diffraction limit, and therefore cannot resolve features much smaller than the wavelength of the electromagnetic waves being used. Imaging beyond diffraction limit is of special importance because of many applications ranging from biological imaging in the optical regime, to magnetic resonance imaging (MRI) at the radio frequencies. To go beyond the diffraction limit, various methods have been recently proposed. In particular, it has been proposed that a negative index metamaterial slab is capable of magnifying the evanescent waves that carry the information of high spatial resolutions, and recovering the fine features of the object at the image plane. This finding has sparked a vast amount of research effort to realize negative index metamaterials at various frequency ranges. Although super-resolution has been demonstrated using negative index metamaterials, the spatial resolution of imaging is extremely sensitive to the presence of material loss, and therefore limiting their applications as practical super imaging devices.
Recently, it was shown that anisotropic media with mixed signs of permittivity tensor elements (the so called “indefinite” media) exhibit a unique dispersion with hyperbolic equi-frequency contour (EFC), allowing the propagation of electromagnetic waves with very large wave vectors. As a result, super-fine features of the objects can be transported by propagating waves through the medium. In comparison with the negative index superlens, the super-imaging through a hyperbolic medium is highly robust against the presence of material loss, therefore, it represents a more practical approach for sub-diffraction imaging. Artificial media with hyperbolic dispersion have been demonstrated recently in the form of metallic wires array, metal-dielectric multilayers, and swiss roll magnetic resonators. However, the fabrication of these media requires time-consuming microfabrication procedures, and the electromagnetic properties cannot be conveniently reconfigured in real time. We have recently shown that a plasma under strong magnetic field exhibit unconfined equi-frequency contour in a similar way as a hyperbolic medium. Here we aim to experimentally demonstrate magnetized plasma for achieving dynamically reconfigurable super-imaging systems, in particular at terahertz frequencies. Since the proposed sub-diffraction imaging using magnetized plasma does not involve complex and time consuming fabrication, it opens a new gate towards cost effective, facile and flexible superimaging devices. In addition, we look into the nontrivial photonic topological orders supported by magnetized plasma, which may lead to highly robust surface states that are protected by topology for microwaves and terahertz waves.
Another aspect of our research is to develop practical optical devices based on plasmonic
metasurfaces. Despite the novel properties of bulk metamaterials, the complexity in manufacturing the three dimensional structures and the strong ohmic loss have prevented device applications based on bulk metamaterials. Metasurfaces, which consist of a single layer of subwavelength antennas, have stood up as a simple alternative for real world applications. During the period of this project, we have developed a functional metasurface design, and realized a number of novel optical devices based on the metasurfaces. The metasuface we have developed consists of an array of gold nanorods with carefully controlled orientations. Each nanorod supports a so-called plasmonic resonance and functions therefore like a tiny optical antenna. The nanorod collects the incident circularly polarized light and re-emits it with a certain retardation in the opposite polarization. The retardation of the light from each nanorod depends thereby only by the orientation angle of the nanorod. In such a way a particular desired phase profile for the wavefront of the light can be obtained. In this project, we have realized a number of novel applications based on metasurfaces, including broadband, high efficiency metasuface holograms, and nonlinear metasurfaces with locally controllable nonlinearity phase. These work open door to powerful control of light in both linear and nonlinear regimes.
Imaging lies in the heart of many important applications in biology, medical sciences, security, and semiconductor industries. Conventional imaging methods are limited by the diffraction limit, and therefore cannot resolve features much smaller than the wavelength of the electromagnetic waves being used. Imaging beyond diffraction limit is of special importance because of many applications ranging from biological imaging in the optical regime, to magnetic resonance imaging (MRI) at the radio frequencies. To go beyond the diffraction limit, various methods have been recently proposed. In particular, it has been proposed that a negative index metamaterial slab is capable of magnifying the evanescent waves that carry the information of high spatial resolutions, and recovering the fine features of the object at the image plane. This finding has sparked a vast amount of research effort to realize negative index metamaterials at various frequency ranges. Although super-resolution has been demonstrated using negative index metamaterials, the spatial resolution of imaging is extremely sensitive to the presence of material loss, and therefore limiting their applications as practical super imaging devices.
Recently, it was shown that anisotropic media with mixed signs of permittivity tensor elements (the so called “indefinite” media) exhibit a unique dispersion with hyperbolic equi-frequency contour (EFC), allowing the propagation of electromagnetic waves with very large wave vectors. As a result, super-fine features of the objects can be transported by propagating waves through the medium. In comparison with the negative index superlens, the super-imaging through a hyperbolic medium is highly robust against the presence of material loss, therefore, it represents a more practical approach for sub-diffraction imaging. Artificial media with hyperbolic dispersion have been demonstrated recently in the form of metallic wires array, metal-dielectric multilayers, and swiss roll magnetic resonators. However, the fabrication of these media requires time-consuming microfabrication procedures, and the electromagnetic properties cannot be conveniently reconfigured in real time. We have recently shown that a plasma under strong magnetic field exhibit unconfined equi-frequency contour in a similar way as a hyperbolic medium. Here we aim to experimentally demonstrate magnetized plasma for achieving dynamically reconfigurable super-imaging systems, in particular at terahertz frequencies. Since the proposed sub-diffraction imaging using magnetized plasma does not involve complex and time consuming fabrication, it opens a new gate towards cost effective, facile and flexible superimaging devices. In addition, we look into the nontrivial photonic topological orders supported by magnetized plasma, which may lead to highly robust surface states that are protected by topology for microwaves and terahertz waves.
Another aspect of our research is to develop practical optical devices based on plasmonic
metasurfaces. Despite the novel properties of bulk metamaterials, the complexity in manufacturing the three dimensional structures and the strong ohmic loss have prevented device applications based on bulk metamaterials. Metasurfaces, which consist of a single layer of subwavelength antennas, have stood up as a simple alternative for real world applications. During the period of this project, we have developed a functional metasurface design, and realized a number of novel optical devices based on the metasurfaces. The metasuface we have developed consists of an array of gold nanorods with carefully controlled orientations. Each nanorod supports a so-called plasmonic resonance and functions therefore like a tiny optical antenna. The nanorod collects the incident circularly polarized light and re-emits it with a certain retardation in the opposite polarization. The retardation of the light from each nanorod depends thereby only by the orientation angle of the nanorod. In such a way a particular desired phase profile for the wavefront of the light can be obtained. In this project, we have realized a number of novel applications based on metasurfaces, including broadband, high efficiency metasuface holograms, and nonlinear metasurfaces with locally controllable nonlinearity phase. These work open door to powerful control of light in both linear and nonlinear regimes.