Field Of Nano-optics Research Articles

Plasmon Driven Nanocrystal Transformation by Aluminum Nano-Islands with an Alumina Layer.

The plasmonic photothermal effects of metal nanostructures have recently become a new priority of studies in the field of nano-optics. Controllable plasmonic nanostructures with a wide range of responses are crucial for effective photothermal effects and their applications. In this work, self-assembled aluminum nano-islands (Al NIs) with a thin alumina layer are designed as a plasmonic photothermal structure to achieve nanocrystal transformation via multi-wavelength excitation. The plasmonic photothermal effects can be controlled by the thickness of the Al2O3 and the intensity and wavelength of the laser illumination. In addition, Al NIs with an alumina layer have good photothermal conversion efficiency even in low temperature environments, and the efficiency will not decline significantly after storage in air for 3 months. Such an inexpensive Al/Al2O3 structure with a multi-wavelength response provides an efficient platform for rapid nanocrystal transformation and a potential application for the wide-band absorption of solar energy.

Photonic Assemblies of Randomly Oriented Nanocrystals for Engineered Nonlinear and Electro-Optic Effects.

Nonlinear crystals that have a noncentrosymmetric crystalline structure, such as lithium niobate (LiNbO3) and barium titanate (BaTiO3) exhibit nonzero second-order tensor susceptibilities (χ(2)) and linear electro-optic coefficients (r ij ). The constraints associated with top-down nanofabrication methods have led to bottom up approaches to harness the strong nonlinearities and electro-optical properties. Here, we present an overview of photonic assemblies made of randomly oriented noncentrosymmetric nanocrystals via bottom-up fabrication methods. In this configuration, nanocrystals can form objects with tunable dimensions, increased complexity, and a great span of symmetry level, ranging from thin layers to spheres. At the same time, according to their shape, photonic assemblies may support optical modes, that is, Mie or guided, which can tailor linear optical properties and enhance nonlinear and electro-optic responses. As a result, assemblies of noncentrosymmetric nanocrystals can form a disruptive platform to realize photonic integrated devices free of etching process and over large surface areas. Last, we foresee potential applications of noncentrosymmetric nanocrystals in various fields of nano-optics and sensing.

Multilayer subwavelength gratings or sandwiches with periodic structure shape light reflection in the tapetum lucidum of taxonomically diverse vertebrate animals.

Eye shine in the dark has attracted many researchers to the field of eye optics, but the initial studies of subwavelength arrangements in tapetum began only with the development of electronic microscopy at the end of the 20th century. As a result of a number of studies, it was shown that the reflective properties of the tapetum are due to their specialized cellular subwavelength microstructure (photonic crystals). These properties, together with the mutual orientation of the crystals, lead to a significant increase in reflection, which, in turn, enhances the sensitivity of the eye. In addition, research confirmed that optical mechanisms of reflection in the tapetum are very similar even for widely separated species. Due to progress in the field of nano-optics, researchers now have a better understanding of the main principles of this phenomenon. In this review, we summarize electron microscopic and functional studies of tapetal structures in the main vertebrate classes. This allows data on the microstructure of the tapetum to be used to improve our understanding of the visual system.

High efficiency and large optical anisotropy in the high-order nonlinear processes of 2D perovskite nanosheets

Abstract Nonlinear nanophotonic devices have brought about great advances in the fields of nano-optics, quantum science, biomedical engineering, etc. However, in order to push these nanophotonic devices out of laboratory, it is still highly necessary to improve their efficiency. Since obtaining novel nanomaterials with large nonlinearity is of crucial importance for improving the efficiency of nonlinear nanodevices, we propose the two-dimensional (2D) perovskites. Different from most previous studies which focused on the 2D perovskites in large scale (such as the bulk materials or the thick flakes), herein we studied the 2D perovskites nanosheets with thickness of ∼50 nm. The high-order nonlinear processes including multi-photon photoluminescence and third-harmonic generation (THG) have been systematically investigated, and it is found the THG process can have a high conversion efficiency up to ∼8 × 10−6. Also, it is observed that the nonlinear responses of 2D perovskites have large optical anisotropy, i.e., the polarization ratio for the incident polarization dependence of nonlinear response can be as high as ∼0.99, which is an impressive record in the perovskite systems. Our findings reveal the properties of high efficiency and huge optical anisotropy in the nonlinear processes of 2D perovskite nanosheets, shedding light on the design of advanced integrated nonlinear nanodevices in future.

Review on Graphene-based Absorbers for Infrared to Ultraviolet Frequencies

The graphene-based absorbers are widely applicable and highly efficient. Graphene has very high electrochemical properties due to which tuning characteristics can be achieved with efficient and broadband absorption response. For this review paper, we have divided the graphene-based absorbers into three categories (Absorber sensors, Solar absorbers, and THz absorbers) based on their applications. We have presented a detailed discussion on various designs and their analysis in this paper. Absorber sensors are mainly applicable in biosensors for the detection of hemoglobin, urine biomolecules using the tuning properties of graphene, and are also applicable in medical, environmental, chemical, biological diagnostic applications. Solar absorbers are applicable in energy harvesting devices. Adding graphene layer in solar absorber design gives the highly efficient and broadband absorption response. THz absorbers are applicable in the THz applications in sensing and imaging devices. Some of the THz absorbers are improving the applications in the new field of nano-optics with 2D material. Graphene and its excellent electrical and optical properties are applied in material designs which create new structures applicable in novel applications like sensing, imaging, solar energy harvesting, etc.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

High-efficiency-and-quality nanostructuring of molybdenum surfaces by orthogonally polarized blue femtosecond lasers

Femtosecond laser-induced periodic surface structures featured by a mask-free and one-step procedure provide a new fascinating prospect for the high precision manufacture applicable to diverse materials, but still face challenges in both the fabrication efficiency and the structure quality. Here, a homogenous large-area nanolithography is implemented on molybdenum surface, through using cylindrical focusing of double temporally delayed blue femtosecond lasers with orthogonal polarizations. The achieved grating structures present some unique features including the ablated narrow groove width of 100 nm, the small period of 245 nm, the smooth ridge profiles, and especially the uniform distribution in a mm-scaled range without bending, spitting and interruption. The calculated structure orientation angle shows an unprecedentedly minimum dispersion value of 5°, indicting a significant improvement on the structure uniformity compared with the observations of the single-beam femtosecond laser irradiation. The simulation results reveal that the transient spatiotemporal correlations between the localized electromagnetic field distributions from the double orthogonally polarized laser pulses constitutes a positive feedback mechanism to regularize the growth of the surface structures. A macro-sized surface pattern of such uniform structures displays good monochromatic colors and excellent broadband antireflection performances. This efficient laser nanolithography facilitates the applications in the fields of nanooptics.

Quantum electrodynamics description of localized surface plasmons at a metal nanosphere

A canonical quantization scheme for localized surface plasmons (LSPs) in a metal nanosphere is presented based on a microscopic model composed of electromagnetic fields, oscillators that describe plasmons, and a reservoir that describes excitations other than plasmons. The eigenmodes of this fully quantum electrodynamic theory show a spectrum that includes radiative depolarization and broadening, including redshifting from the quasistatic LSP modes with increasing particle size. These spectral profiles correctly match those obtained with exact classical electrodynamics (Mie theory). The present scheme provides the electric fields per plasmon in both near- and far-field regions whereby its utility in the fields of quantum plasmonics and nano-optics is demonstrated.

Sights Unseen

Can we make mice see the invisible? Renaud Bachelot reviews striking developments in the emergent field of nano-optics and nanophotonics—particularly, new results which explore making infrared visible to mice. To what degree might this be practical for humans?

Role of Geometric Shape in Chiral Optics

The distinction of chiral and mirror symmetric objects is straightforward from a geometrical point of view. Since the biological as well as the optical activity of molecules strongly depend on their handedness, chirality has recently attracted high interest in the field of nano-optics. Various aspects of associated phenomena including the influences of internal and external degrees of freedom on the optical response have been discussed. Here, we propose a constructive method to evaluate the possibility of observing any chiral response from an optical scatterer. Based on solely the T-matrix of one enantiomer, planes of minimal chiral response are located and compared to geometric mirror planes. This provides insights into the relation of geometric and optical properties and enables identifying the potential of chiral scatterers for nano-optical experiments.

The preparation, characterization and application of ultra-smooth, low-loss plasmonics noble metal films

Since its discovery, plasmonics has become one of the most popular topics in the field of nano-optics due to its unprecedented capability of harvesting and localizing electromagnetic fields down to diffraction-unlimited length scales. However, the application of plasmonic effects has long been hindered by the difficulties in controlling the surface morphology and reducing the optical loss of noble metal films, which not only hinders the progress of its experimental research, but also cast a shadow on its application prospects in many fields. With the fast development of nanofabrication technologies, the surface roughness and optical loss of noble metal films is getting closer the theoretical expectation, while the preparation technology is becoming precisely controllable, which lets it play an important role not only in the traditional field, but in may emerging fields as well. In this review, we systematically summarize the recent progress in preparation, characterization and application of ultra-smooth, low-loss noble metal films.

Resonant behavior of a single plasmonic helix

Chiral plasmonic nanostructures will be of increasing importance for future applications in the field of nano optics and metamaterials. Their sensitivity to incident circularly polarized light in combination with the ability of extreme electromagnetic field localization renders them ideal candidates for chiral sensing and for all-optical information processing. Here, the resonant modes of single plasmonic helices are investigated. We find that a single plasmonic helix can be efficiently excited with circularly polarized light of both equal and opposite handedness relative to that of the helix. An analytic model provides resonance conditions matching the results of full-field modeling. The underlying geometric considerations explain the mechanism of excitation and deliver quantitative design rules for plasmonic helices being resonant in a desired wavelength range. Based on the developed analytical design tool, single silver helices were fabricated and optically characterized. They show the expected strong chiroptical response to both handednesses in the targeted visible range. With a value of 0.45 the experimentally realized dissymmetry factor is the largest obtained for single plasmonic helices in the visible range up to now.

Theoretical study for fabricating elliptical subwavelength nanohole arrays by higher-order waveguide-mode interference

A theoretical method is proposed for fabricating elliptical subwavelength nanohole arrays (ESNA) based on the higher-order waveguide mode (WM) interference in an asymmetric metal-cladding dielectric waveguide (AMDW). The finite-element method is used to simulate the optical field distributions in the AMDW. With excitation by 442-nm transverse magnetic (TM) polarized light, the metal layer is a 40-nm-thick silver film and the waveguide layer is a 9650-nm-thick photoresist that can support many guided modes by virtue of its thickness. The interference of TM51 WMs is used to demonstrate the proposed method for fabricating ESNA. The major and minor axes of the nanohole are obtained theoretically as 110 nm and 98 nm, respectively. With a certain photoresist thickness, ESNA with various periods can be fabricated by selecting different guided modes. The proposed method is a simple way to produce ESNA and could have wide applications in the field of nano-optics.

Optical Features of the Silica Sol–Gel Derived Glasses Doped with Copper Selenide Nanoparticles

In the field of semiconductor nanooptics, copper chalcogenides have challenged a novel direction associated with nontrivial optical features in the near IR range important for applications. We consider this phenomenon in the silica sol–gel derived glasses doped with copper selenide nanoparticles. They were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy and optical absorption spectroscopy. An origin of the near IR optical features is discussed involving both the plasmon resonance concept extended to the self-doping of chalcogenides with a variable stoichiometry and the effect of Cu2+ impurity-generated intraband levels providing linear and nonlinear optical response of these materials.

Semi-closed T-shaped-disk waveguide filter based on surface-plasmon-induced transparency

Filter is the core communication device in optical integrated chip. In recent years, plasma-induced transparency in surface plasmon (SPP) subwavelength waveguide photonic deviceshas become a research hotspot in the field of nano optics. The plasmon-induced transparency (PIT) is a phenomenon that the original absorption region produces a sharp transparent window due to the interaction among different resonant modes of SPPs, therefore, a higher resolution and quality factor surface plasmons can be obtained by using this feature to design a metal-medium-metal (MIM) waveguide structure filter. However, due to the Ohmic loss caused by metal parts, further research is needed on how to effectively improve transmission efficiency and achieve better frequency selection and filtering effect while reducing filter bandwidth in MIM waveguide filter. Based on the transmission and coupling characteristics of SPPs, an MIM waveguide filter with semi-closed T-waveguide side coupled disc cavity is proposed.Its transmission characteristics are studied by using the finite element method. The results show that a narrow-band transmission peak based on plasma-induced transparency appears in the transmission spectrum. Through theoretical analysis and mode field distribution, the physical mechanism of generating the PIT transparent peak and valley values on both sides is effectively explained. Compared with the traditional straight waveguide structure, the curved waveguide structure can generate the bilateral coupling effect, which can make resonant interaction stronger. Meanwhile, the numerical study shows that the approximately linear adjustment of filter wavelength can be achieved by changing the length of branches, the radius of the disk cavity and the refractive index of the medium in the cavity through external modulation. Further, the gain medium is embedded in the disk cavity, which enhances its local ability to emit light, strengthens the mode resonance effect, and realizes the compression filter pass-band bandwidth while effectively improving the structural transmittance, compared with similar filters. The research results provide an effective theoretical reference for designing the high resolution narrowband filter.

Tailoring a periodic metal nanoantenna array using low cost template-assisted lithography

Tailoring the optical response of metal nanoparticles by controlling their morphology is a key topic in the field of nano-optics. Here, a simple approach for the fabrication of tunable plasmonic nanostructures by nanosphere lithography is presented.

Theoretical study of multiexposure zeroth-order waveguide mode interference lithography

A new nanolithography technique in which sample rotation is incorporated into zeroth-order waveguide mode interference lithography is proposed in this report. A 325-nm laser was used to excite zeroth-order waveguide modes, which were loaded by an asymmetric metal-cladding dielectric waveguide structure. The optical field intensity distribution of zeroth-order waveguide modes interference is numerically simulated using the finite element method. The lithography sample consisted of a glass substrate, Al film, and photoresist film, and the rotation operation on the sample is expressed in coordinate matrix transformation. Various subwavelength structures, such as two-dimensional square lattices, two-dimensional hexagonal closed-packed lattices,and circular gratings, were obtained through double, triple, and continuous exposure. These subwavelength structures with different sizes can be produced by changing the thickness of the photoresist. The subwavelength structures simulated with various shapes and sizes can be applied to the field of nano-optics. The proposed technique provides a flexible and promising approach for interference nanolithography because of its simplicity and low cost.

Exploring the Magnetic and Electric Side of Light through Plasmonic Nanocavities.

Light-matter interactions are often considered to be mediated by the electric component of light only, neglecting the magnetic contribution. However, the electromagnetic energy density is equally distributed between both parts of the optical fields. Within this scope, we experimentally demonstrate here, in excellent agreement with numerical simulations, that plasmonic nanostructures can selectively manipulate and tune the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement or decay of magnetic and electric emission from trivalent europium-doped nanoparticles in the vicinity of plasmonic nanocavities, designed to efficiently couple to either the electric or magnetic emission of the quantum emitter. Specifically, by precisely controlling the spatial position of the emitter with respect to our plasmonic nanostructures, by means of a near-field optical microscope, we record local distributions of both magnetic and electric radiative local densities of states (LDOS) with nanoscale precision. The distribution of the radiative LDOS reveals the modification of both the magnetic and electric optical quantum environments induced by the presence of the metallic nanocavities. This manipulation and enhancement of magnetic light-matter interaction by means of plasmonic nanostructures opens up new possibilities for the research fields of optoelectronics, chiral optics, nonlinear and nano-optics, spintronics, and metamaterials, among others.

Enhancing Magnetic Light Emission with All-Dielectric Optical Nanoantennas.

Electric and magnetic optical fields carry the same amount of energy. Nevertheless, the efficiency with which matter interacts with electric optical fields is commonly accepted to be at least 4 orders of magnitude higher than with magnetic optical fields. Here, we experimentally demonstrate that properly designed photonic nanoantennas can selectively manipulate the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement of magnetic emission from trivalent europium-doped nanoparticles in the vicinity of a nanoantenna tailored to exhibit a magnetic resonance. Specifically, by controlling the spatial coupling between emitters and an individual nanoresonator located at the edge of a near-field optical scanning tip, we record with nanoscale precision local distributions of both magnetic and electric radiative local densities of states (LDOS). The map of the radiative LDOS reveals the modification of both the magnetic and electric quantum environments induced by the presence of the nanoantenna. This manipulation and enhancement of magnetic light-matter interaction by means of nanoantennas opens up new possibilities for the research fields of optoelectronics, chiral optics, nonlinear and nano-optics, spintronics, and metamaterials, among others.

Plasmon–emitter interaction using integrated ring grating–nanoantenna structures

Overcoming the diffraction limit to achieve high optical resolution is one of the main challenges in the fields of plasmonics, nanooptics and nanophotonics. In this work, we introduce novel plasmonic structures consisting of nanoantennas (nanoprisms, single bowtie nanoantennas and double bowtie nanoantennas) integrated in the center of ring diffraction gratings. Propagating surface plasmon polaritons (SPPs) are generated by the ring grating and coupled with localized surface plasmons (LSPs) at the nanoantennas exciting emitters placed in their gap. SPPs are widely used for optical waveguiding but provide low resolution due to their weak spatial confinement. In contrast, LSPs provide excellent sub-wavelength confinement but induce large losses. The phenomenon of SPP–LSP coupling witnessed in our structures allows for achieving more precise focusing at the nanoscale, causing an increase in the fluorescence emission of the emitters. Finite-difference time-domain simulations as well as experimental fabrication and optical characterization results are presented to study plasmon–emitter coupling between an ensemble of dye molecules and our integrated plasmonic structures. A comparison is given to highlight the importance of each structure on the photoluminescence and radiative decay enhancement of the molecules.

Numerical investigation of the Rayleigh hypothesis for electromagnetic scattering by a particle

The validity of the Rayleigh hypothesis (RH) has been a long-standing issue in the applicability of the T-matrix method to near-field calculations, and despite numerous theoretical works, the practical consequences for numerical simulations have remained unclear. Such calculations are increasingly important in the field of nano-optics, for which accurate and efficient modeling tools are in high demand. We here tackle this challenge by investigating numerically the convergence behavior of series expansions of the electric field around spheroidal particles, which provides us with unambiguous examples to clarify the conditions of convergence. This study is made possible by the combination of alternative methods to compute near-fields accurately, and crucially, the recent improvements in the calculation of T-matrix elements free from numerical instabilities, as such errors would otherwise obfuscate the intrinsic convergence properties of the field series. The resulting numerical confirmation for the range of validity of the RH, complemented by a better understanding of the convergence behavior of the field expansions, is a crucial step toward future developments.