So far, metalenses have only been studied in imaging optics, where a point from the object space is mapped to a corresponding point in the image space. Here we explore metalenses and metamirrors for dealing with the optimal transfer of... more
So far, metalenses have only been studied in imaging optics, where a point from the object space is mapped to a corresponding point in the image space. Here we explore metalenses and metamirrors for dealing with the optimal transfer of light energy. Owing to its compactness and high design flexibility, metasurface-based flat optics may open new opportunities in the nonimaging field, which deals with light concentration and illumination. The building blocks of metalenses are subwavelength-spaced scatterers. By suitably adjusting their shape, size, position, and orientation , one can control the light spatial distribution, as is desired in nonimaging problems. In this Letter, we introduce nonimaging metaoptics, review its basics, and briefly explore three cases: the compound-metasurface concentra-tor [analogous to the compound parabolic concentrator (CPC)], the total internal reflection (TIR) metalens (analogous to the TIR lens), and a simple condensing metalens.
The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for... more
The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for alternative optimal antenna designs. Here we subject a checkerboard-type, initially random array of gold cubes to evolutionary optimization. To illustrate the power of the approach, we demonstrate that by optimizing the near-field intensity enhancement, the evolutionary algorithm finds a new antenna geometry, essentially a split-ring–two-wire antenna hybrid that surpasses by far the performance of a conventional gap antenna by shifting the n = 1 split-ring resonance into the optical regime.
Reactive oxygen and nitrogen species play a critical role in many free radical mediated degenerative diseases and in aging. Oxidative stress is the state of a diminished capacity of a biological system to counteract an overproduction or... more
Reactive oxygen and nitrogen species play a critical role in many free radical mediated degenerative diseases and in aging. Oxidative stress is the state of a diminished capacity of a biological system to counteract an overproduction or invasion of reactive oxygen species and other radicals. Nanotechnology is an enable technology that has the potential to address the issues relevant to oxidative stress. Nanoparticle antioxidants constitute a new wave of antioxidant therapies for disease prevention and treatment in the field of oxidative stress and associated disorders such as type 2 diabetes. Specific nanoconstructs are also reported to have anti-inflammatory activities. CNTs and CNFs used as integral part of polymer composites are able to exhibit an antioxidant effect in these materials because of their radical accepting capacity. This concise review is mainly focused on nanoparticles that are now increasingly getting recognized owing to various studies conducted over the past couple of years. Recent reports have demonstrated that several types of nanoparticles act as potent free radical scavengers and antioxidants. The characterization and functioning of various inorganic nanoparticles along with the mechanism of their antioxidant activity and their use in the field of oxidative stress has been explored. Their action is mediated through free radical scavenging activity by reducing the concentration of reactive oxygen and nitrogen species, thus acting as antioxidants by themselves. Given these properties, the potential applications of some selected antioxidant nanoparticles in alleviating oxidative stress are discussed in this review.
Dynamic generation of obitial angular momentum (OAM) of light has enabled complex manipulation of micro-particles, high-dimension quantum entanglement and optical communication. We report an analog vortex transmitter made of one... more
Dynamic generation of obitial angular momentum (OAM) of light has enabled
complex manipulation of micro-particles, high-dimension quantum entanglement and
optical communication. We report an analog vortex transmitter made of one bilaterally
symmetric grating and an aperture, emitting optical vortices with the average OAM
value continuously variant in the entire rational range. Benefiting from linearly-varying
transverse dislocation along its axis of symmetry, this diffractive transmitter possesses
extra degree of freedom in engineering broadband optical vortices meanwhile
preserving a novel spiniform phase with equally spaced singularities. It unlimitedly
increases the average OAM of light by embracing more singularities, which is
significantly different from that for Laguerre-Gaussian (LG) and Bessel vortex beams.
Realizing analog generation of OAM in a single device, this technique can be potentially
extended to other frequencies and applied to a wide spectrum of developments on
quantum physics, aperiodic photonics and optical manipulation.
This work presents analytical, numerical and experimental demonstrations of light diffracted through a logarithmic spiral (LS) nanoslit, which forms a type of switchable and focustunable structure. Owing to a strong dependence on the... more
This work presents analytical, numerical and experimental demonstrations of light diffracted through a logarithmic spiral (LS) nanoslit, which forms a type of switchable and focustunable structure. Owing to a strong dependence on the incident photon spin, the proposed LS-nanoslit converges incoming light of opposite handedness (to that of the LS-nanoslit) into a confined subwavelength spot, while it shapes light with similar chirality into a donut-like intensity profile. Benefitting from the varying width of the LS-nanoslit, different incident wavelengths interfere constructively at different positions, i.e., the focal length shifts from 7.5 μm (at λ = 632.8 nm) to 10 μm (at λ = 488 nm), which opens up new opportunities for tuning and spatially separating broadband light at the micrometer scale.
Communities are reluctant to embrace new technologies where there is inadequate disclosure about the potential impacts on health or safety. Community outrage surrounding the recent widespread use of asbestos, despite the known health... more
Communities are reluctant to embrace new technologies where there is inadequate disclosure about the potential impacts on health or safety. Community outrage surrounding the recent widespread use of asbestos, despite the known health impacts, has led to distrust and scepticism towards new and emerging technologies which are heralded as revolutionary. Molecular genetics and nanotechnology are two examples of such technologies
Confined electromagnetic fields are created at the surface of various substrates such as indium-tin-oxide (ITO) and goldfilms. Two scanning tunneling microscope tips (Pt–Ir and W) are used to create a localized perturbation. With ITO as a... more
Confined electromagnetic fields are created at the surface of various substrates such as indium-tin-oxide (ITO) and goldfilms. Two scanning tunneling microscope tips (Pt–Ir and W) are used to create a localized perturbation. With ITO as a substrate, an evanescent field is observed without a tip-substrate interaction. Conversely, with a goldfilmsurface formation of “gap modes,” the particle-substrate cavity is seen. Gap modes at the interface of a metallic film are involved essentially when the modulation amplitude of the particle is below 100 nm. In the context of apertureless near-field microscopy, this demonstrates the influence of tip-surface coupling in scanning plasmon near-field microscope (SPNM) signals. The strong interaction of the tip with the metal substrate, through its surface plasmon, when combined with SPNM, may result in inaccuracies in the claimed chemical identification or intrinsic optical properties of the particle.
We report on an experimental investigation on surface plasmon polariton SPP propagation and interaction on two-dimensional arrays of differing symmetry properties. Providing the required symmetry variations and forming the basis of the... more
We report on an experimental investigation on surface plasmon polariton SPP propagation and interaction on two-dimensional arrays of differing symmetry properties. Providing the required symmetry variations and forming the basis of the arrays are tailor designed nanostructures. We demonstrate that as a result of a 120° symmetry presence, our triquetra-rotor nanostructures can be used for SPP guiding and propagation direction control. As a result, the polarization angle at which the far field SPP related minimum reflectivity occurs can be predetermined by design characteristics and orientation of the nanostructures.
Metal nanoparticles play a key role in sensing and imaging. Here we demonstrate the detection of metal particles down to 5 nm in size with a signal-to-noise ratio of 7 using interferometric cross-polarization microscopy at ultralow... more
Metal nanoparticles play a key role in sensing and imaging. Here we demonstrate the detection of metal particles down to 5 nm in size with a signal-to-noise ratio of 7 using interferometric cross-polarization microscopy at ultralow excitation powers (1 μW) compatible with single molecule detection. The method is background-free and induces no heating as it operates far from plasmonic resonance. The combination of unlimited observation time and protein-sized metal nanoparticles has great potential for biophysical applications.
