Metal Mirrors Research Articles

Results of the Chemical Composition Analysis of Metal Mirrors of the Golden Horde Period Excavated in Mangup

The collection of metal mirrors of the Golden Horde period of the Mangup hillfort, situated in the south-western part of the Crimea, includes 19 items. The chemical composition of 17 mirrors was studied using an M1 Mistral (Bruker) X-ray fluorescence spectrometer. The measurements were carried out at three points on the front and back sides of the mirrors. Averages were calculated for each side. According to the results of the analysis, the mirrors are made of pewter bronze with additives of lead. The content of pewter in the alloy of mirrors from Mangup ranged from 10 to 38%. The share of lead was 1-17%. Analysis of dopants made it possible to distinguish three types of alloys. 11 mirrors are made of pewter-lead bronze (Cu + Sn + Pb), 4 mirrors are made of pewter-lead-antimony bronze (Cu + Sn + Pb + Sb), 1 mirror is made of tin-lead-zinc bronze (Cu + Sn + Pb + Zn). The differences between the identified types of alloys probably reflect formula variations of the “mirror” alloy composition within the unified craft tradition. The comparison of the chemical composition of the studied mirrors with the items from other regions gave the following results. The closest analogies to mirrors from Mangup were found on the territory of the Volga and Don rivers regions. Their alloy contains similar proportions of the main components. The only difference is the set of ore impurities. The results of the analysis of the chemical composition suggest the producing of Mangup mirrors in the Volga region. The morphological and stylistic similarities of mirrors from both regions can be considered as an additional argument in favor of this thesis.

An Experimental Study on Simultaneous Use of Metal Fins and Mirror to Improve the Performance of Photovoltaic Panels

The world is inconceivable without an everlasting demand for energy. Nowadays, various kinds of renewable energies, such as solar energy, are developing rapidly, since they have the least negative environmental impacts. Irradiation intensity is one the most important parameters in photovoltaic (PV) technology, and so integration of mirrors with a PV module can improve its performance. Mounting mirrors increases the radiation intensity but, at the same time, raises the surface temperature, which in turn reduces the electrical efficiency. The novelty of this study is keeping the cell temperature low despite receiving more radiation by installing 10 aluminum fins on the back of the panel. All tests were experimentally performed in the hot climate of Dezful, Iran. As a result, the best tilt angle of the mirror was found at 30°, where the output power was enhanced by 3.3% and electrical efficiency was reduced by 0.5% compared with the conventional case. When aluminum fins were added as heat sinks, both output power and electrical efficiency were enhanced by 11.4% and 13.1%, respectively. Moreover, comprehensive discussions on both energy and exergy are provided. The entropy generation was also calculated and accordingly, the case of PV 30 + fin generates 1.6% less entropy than the base one.

Effect of Mirror Quality on Optical Response of Nanoparticle‐on‐Mirror Plasmonic Nanocavities

AbstractAs an essential part of nanoparticle‐on‐mirror (NPoM) plasmonic nanocavities, metal mirrors play an important role not only in determining the optical response of the nanocavities but also their application performance. Here the effect of mirror quality on the optical response of nanosphere‐on‐mirror (NSoM) and nanocube‐on‐mirror (NCoM) nanocavities is experimentally studied. Polycrystalline sputtered gold films (SGFs), template‐stripped gold films (TSGFs), and single‐crystalline gold microflakes (GMFs) are investigated and compared. Due to the great improvement in the surface roughness that can minimize fluctuations in the gap morphology, NSoM and NCoM nanocavities formed on smooth TSGFs and GMFs have a better cavity‐to‐cavity homogeneity in the scattering spectrum than those formed on comparably rougher SGFs. In addition, there is an obvious change in the spectral positions of the resonance modes of NSoM and NCoM nanocavities formed on SGFs due to the variation in the gap morphology, which is reproduced very well by theoretical calculations based on measured dielectric functions of the gold films. Finally, due to the reduction in electron scattering losses from SGFs to TSGFs and GMFs, an increase in the quality factors and scattering intensities of the resonance modes is observed for nanocavities formed on the corresponding films.

Design of a metal-based deformable mirror for orthogonal beam deflection and highly dynamic beam oscillation.

We report on an opto-mechanical metal mirror design for highly dynamic, diffraction-limited focus shifting. Here, the mechanical geometry of the membrane is of crucial interest as it must provide sufficient optical performance to allow for diffraction limited focussing and have a high mechanical eigenfrequency to provide dynamic motions. The approach is the analytical consideration of the plate theory and provides the basis for a parameterized finite element model. By means of an finite element analysis (FEA), essential steps for the optimization of the mirror design with respect to a wide range of optical power and a high operating frequency are shown. To verify the results of the FE analysis, the deformed surface is decomposed into Zernike coefficients. An analysis of the point spread function is performed to evaluate the optical performance. For dynamic evaluation a modal and a harmonic vibration analysis are conducted. The opto-mechanical design allows a biconical deformation of the mirror surface, enabling the generation of a diffraction-limited spot diameter in the adjustment range of ±1.2 dpt. The surface shape error in this range is 53 nm. The dynamic analysis shows the first excited eigenfrequency at 21.6 kHz and a diffraction-limited operation frequency at 9.5 kHz. This paper provides an alternative design approach for highly dynamic beam oscillation in the Z direction, forming a complement to highly dynamic X-Y scanning systems.

Extremely wide-angle nonreciprocal thermal emitters based on Weyl semimetals with dielectric grating structure

Although various nonreciprocal thermal emitters have been suggested to break the balance between absorption and emission, the majority can only achieve nonreciprocal effect at one certain angle, and the angular range in which these structures exhibit nonreciprocal effect is heavily restricted. In this work, the scheme to realize extremely wide-angle nonreciprocal thermal radiation effect is proposed and investigated. It is achieved by placing a dielectric grating atop a Weyl semimetal film backed with a metal mirror. The results show that the emitter exhibits strong nonreciprocal radiation at the wavelength of 15.98 μm when the incident angle is 30°. What's more, the strong nonreciprocal radiation can be achieved in a wide angular range. Such behavior results from the guided mode resonance, which is revealed by investigating the distribution of electromagnetic field at the resonant wavelength and is also confirmed by the dispersion relation of guided mode. This work provides a new approach to the design of novel nonreciprocal thermal emitters.

Broadband Graphene-Based Electro-Optic Chiral Polarization Conversion for Terahertz Pulse Shaping

Terahertz (THz) radiation is ideally suited for noninvasive testing and short-distance data transmission. Actively controlling the polarization of THz waves is highly desirable in measurement systems. Although significant developments of THz active devices has been achieved through introducing the electromagnetic resonance structure (e.g., metamaterials), the bandwidth is limited. Here, we propose a graphene-based electrically reconfigurable polarization conversion across a broadband THz region (0.3 to 0.9 THz) for controlling the chiral polarization of terahertz pulse. By electrically controlling the graphene conductivity, we can switch the device reflection in-between total internal reflection and metal mirror reflection to realize a frequency-independent phase change, which enables a tunable waveplate with a high dynamic range for manipulating the polarization of THz waves. Because of the frequency-independent modulation property, we achieved tunable chiral polarization THz waveforms in the time domain for the first time, from right-handed to left-handed polarization. This work opens up a new mechanism for designing novel THz modulators for THz circular dichroism.

Manipulation of optical bound states in the continuum in a metal-dielectric hybrid nanostructure

Optical bound states in the continuum (BICs) are spatially localized states with vanishing radiation, despite their energy embedded in the continuum spectrum of the environment. They are expected to greatly enhance light–matter interaction due to their long lifetime and high quality factor. However, the BICs in all-dielectric structures generally exhibit large mode volumes and their properties are difficult to manipulate. In this paper, we propose a metal–dielectric hybrid nanostructure where a silver film is inserted into the silicon (Si) substrate under the Si nanopillar array. We show that symmetry-protected BIC in this system can couple with surface plasmon polaritons (SPPs) to form a hybridized mode. Compared with previous symmetry-protected BICs in all-dielectric structures, the SPP-coupled BIC has a significantly decreased mode volume, and its corresponding electric field is strongly localized below the Si nanopillars. We also show that the SPP mode makes the original polarization-independent symmetry-protected BIC become polarization-dependent. In addition, we demonstrate that the silver film in the considered structure can induce a metal mirror effect. The destructive interference between the magnetic dipole inside the Si nanopillars and the mirror magnetic dipole in the silver film can lead to the formation of accidental BICs. Our hybrid structure provides a versatile platform for the manipulation of light–matter interaction in the nanoscale.

Low-profile and compact retroreflector enabled by a wide-angle and high-efficiency metalens

In this paper, a low-profile metasurface retroreflector based on an ultra-thin wide-angle and high-efficiency metalens is proposed and investigated. Owing to its stable high transmission magnitude and the insensitive phase shift of the proposed meta-atoms within a continuous wide-angle range, the designed metalens can efficiently focus both normal and various oblique incident angle waves to a pre-designed curved trajectory continuously. By placing a concave metal mirror which is exactly coincide with the determined focused spots, the cascaded structure thus can realize backscattering enhancement working at a continuous wide-angle range. A prototype is also fabricated, measured and characterized and the experimental results verify that the proposed retroreflector can perform an excellent backscattering enhancement within a stable 3 dB monostatic RCS for almost ±30° angle range. Moreover, the relationship between the focusing performances of wide-angle metalens (e.g., focused spot power intensity, focusing efficiency and positions) and the backscattering enhancement of cascaded wide-angle retroreflector is established and highlighted. Besides, its excellent backscattering enhancement (the absolute RCS level and angular range) can be compared to some traditional widely-used radar retroreflectors like trihedral corner reflector or Luneburg lens reflector for the similar physical size. The proposed metalens retroreflector also posses of a noticeable working bandwidth of about 0.2 GHz within X band. The presented retroreflective device is promising to develop into a low-profile, light-weight and cost-effective wide-angle retroreflector thus enabling various applications for modern microwave engineering.

Near-Perfect TMOKE in Photonic Crystal Structures for Sensing Devices With High Figure of Merit

Near-perfect transverse magneto-optical Kerr effect (TMOKE), which is realized by sandwiching a magnetic-optical film between a photonic crystal (PhC) structure and a metallic mirror, is studied. Near-unity amplitude in TMOKE is observed owing to the excitation of Tamm plasmon polaritons (TPPs) at the interface between the PhC and the metallic mirror. The physical origin behind such giant enhancement of TMOKE is disclosed by studying the magnetic field distributions at resonance and also confirmed by the reflection spectra of the top PhC and the bottom continuous metallic film. Besides, the suitability and the sensitivity of the proposed structure for sensing both gas and aqueous mediums are also illustrated in the last. And it is found that the excellent performance with the averaged figure of merit (FoM) on the order of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.8\times10^{3}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.7\times10^{3}$ </tex-math></inline-formula> can be achieved for sensing gas and aqueous mediums, respectively. We hoped that this work will prompt the development of data magnetic storage, optical filters, waveguide isolators, and novel sensors with improved sensitivity.

Dedicated Boundary Element Modeling for Nanoparticle‐on‐Mirror Structures Incorporating Nonlocal Hydrodynamic Effects

AbstractA boundary element modeling for predicting the plasmonic response from a Nanoparticle‐on‐Mirror (NPoM) structure is proposed. The NPoM can be considered as one of the most important platforms in the research on nanophotonics. Instead of using the local response model to describe the optical response of metals, the nonlocal hydrodynamic model is used to account for the dynamics of free electrons in the metallic NP and the metallic mirror beneath. A system of boundary integral equations (BIEs) is derived to describe the interaction of light with the NPoM structure. The BIEs are solved by the boundary element method. To validate the implementation, two exemplary structures are considered: the Nanosphere‐on‐Mirror structure and the Nanocube‐on‐Mirror structure. By contrasting with the results from previous works and the results from a generalized T‐matrix method, both a qualitative and quantitative agreement in the near field and the far field regimes are observed.

Design, fabrication, and testing of an all-metal ultra-compact telescope.

The design, fabrication, and testing of an all-metal four-mirror telescope for high-resolution remote sensing is presented in this paper. The system works in the visible (VIS) band and is designed with a focal length of 1406 mm, an aperture of 200 mm, and a full field of view (FOV) of 1.32°. The mechanical structure is designed to realize the snap-together alignment. The primary mirror (M1) and tertiary mirror (M3) are designed as a co-substrate element to simplify the fabrication and alignment. The telescope's weight is 3.5 kg, and the volume is just φ230×220mm3. Metallic mirrors are fabricated with single-point diamond turning, and post-polishing is used to correct the mirror's surface form deviation and remove turning tool marks effectively. After polishing, the RMS value of the mirror surface form deviation of the final mirror can reach 0.02λ at λ=632.8nm, and the surface roughness Ra value is about 1.83 nm. Benefiting from the all-metal mechanical design, the alignment process of the telescope is fast and accurate. The interferometric wavefront, modulation transfer function, and focal length of the telescope are measured, and the results demonstrated that it achieves the near-diffraction-limited imaging performance.

Effects of high energy electron and X-ray irradiation on the morphology, microstructure and reflectivity of cast speculum metal mirror

The effects of irradiation of cast speculum metal mirrors using high-energy electrons (6 MeV and 9 MeV) and X-rays (6 MeV and 10 MeV) from a medical linear accelerator setup are studied in detail for the first time. Analyses using the techniques of X-ray diffraction, atomic force microscopy and Ultraviolet–Visible spectroscopy reveal that the irradiation causes some significant microstructural and morphological changes on the surface of speculum metal leading to the modifications of surface properties and hence the reflectivity of the material. From AFM morphology and XRD pattern, it is evident that the electron beam irradiation affects the surface topography and crystallographic properties of the material more at 6 MeV than 9 MeV. The optical studies suggest a significant reduction in Ultraviolet–Visible reflection after electron irradiation. However, X-ray irradiation of speculum metal provides an enhancement of reflection in the Ultraviolet–Visible region. Irradiation with high-energy electrons affects significantly the amount of absorption in the ultraviolet region. Moreover, an inverse relationship between crystallinity and visible reflectivity is inferred after electron and X-ray irradiations. These results may open up promising possibilities for this alloy to use in future space missions under high-energy irradiation due to its capacity to resist energetic particles and electromagnetic radiation without much material destruction.

Reflective metalens with an enhanced off-axis focusing performance

Metalenses are one of the most promising metasurface applications. However, all-dielectric reflective metalenses are rarely studied, especially regarding their off-axis focusing performance. After experimentally studying the material optical properties in this work, we propose reflective metalens based on titanium dioxide (TiO2) and silicon dioxide (SiO2), which operate at a visible wavelength of 0.633 µm. Unlike conventional reflective metalenses based on metallic mirrors, the proposed device was designed based on a modified parabolic phase profile and was integrated onto a dielectric distributed Bragg reflector periodic structure to achieve high reflectivity with five dielectric pairs. The focusing efficiency characteristics of the metalens were experimentally studied for beam angles of incidence between 0∘ and 30∘. The results reveal that the focusing efficiency for the modified metalens design remains higher than 54%, which is higher than 50%, making it promising for photonic miniaturization and integration.

Performance Improvement of Red InGaN Micro-LEDs by Transfer Printing From Si Substrate Onto Glass Substrate

Red micro light-emitting diodes (micro-LEDs) on silicon substrates are important components for realizing large-scale and low-cost micro-LED displays. Recently, InGaN red micro-LEDs have received enormous attention because their external quantum efficiency (EQE) is not significantly affected by size effect and they are compatible with existing green and blue LED material systems. Here, taking advantage of the easy removal of silicon substrates, we successfully achieved the transfer printing of InGaN red micro-LEDs. By removing the light-absorbing Si substrate and introducing a metal mirror, the transfer printed micro-LEDs exhibited better color purity, higher optical power, and higher EQE. At 0.5 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the optical power of micro-LEDs on glass was 300% higher than that of micro-LEDs on silicon. And the peak EQE of transfer printed micro-LEDs was 2.3 times that of micro-LEDs on native substrate. This work is applicable to most transfer printing techniques requiring PDMS stamps, and shows the potential to realize InGaN-based full-color micro-LED displays by mass transfer in the future.

High-Performance Grating Coupler Array on Silicon for a Perfectly-Vertically Mounted Multicore Fiber

High performance grating coupler array for coupling of a silicon photonic chip to a multi-core fiber mounted perfectly vertical to the chip surface is proposed and demonstrated. Experimental results show a low coupling loss of −0.8 dB with 1-dB bandwidth of 47 nm, a low back reflection of <−15.8 dB in about 40 nm wavelength range, a channel non-uniformity of 0.9 dB, and crosstalk of <−40 dB. These improved results attribute to the design of embedding the diffractive grating in a one-port cavity formed by partially and perfectly reflecting Bragg gratings on the silicon chip and a metal mirror on the chip surface.

Design of tunable dual-band terahertz perfect absorber base on graphene

In this paper, a novel tunable dual-band graphene-based perfect absorber which features a three-layer structure consisting of a monolayer graphene sheet and a metallic mirror separated by a thin Si layer with circular microcavity array is designed and systematically investigated. The simulation results show that the two perfect absorption peaks (99.7% and 99.5%) are achieved at 4.13 and 4.38 THz. The two resonance modes are caused by different electric and magnetic field distributions, resulting in different tuning properties. The absorption peaks could be tuned by adjusting the chemical potential of the monolayer graphene. In addition, the influences of the structural parameters such as period, thickness of the Si layer, depth and radius of the circular microcavity on the absorption characteristics of the absorber have been studied and presented.

A High Efficiency and Precision Smoothing Polishing Method for NiP Coating of Metal Mirror.

The NiP coating has excellent wear and corrosion resistance, and electroless nickel-phosphorus coating is one of the best measures for surface modification of metal optical devices. The NiP layer could be processed by single-point diamond turning (SPDT). However, the periodic marks on the surface of the NiP coating processed by SPDT will lead to diffraction and stray light, which will reduce the reflectivity and image quality of the mirror. This paper studied smoothing polishing based on chemical mechanical polishing to remove turning periodic marks efficiently. Firstly, we studied the chemical corrosion and mechanical removal mechanism of smoothing polishing of the NiP coating through theoretical analysis. Then, the influencing factors of processing the quality of smoothing polishing are analyzed, and the optimal machining parameters and polishing slurry formula are formulated. Finally, through the developed process, the surface roughness of Root Mean Square (RMS) 0.223 nm is realized on the NiP coating, and an ultra-smooth surface that can meet the service accuracy of a hard X-ray mirror is obtained. Our research simplifies the high-precision machining process of the NiP coating and improves the machining efficiency. Therefore, it can be used as a new high-precision manufacturing NiP coating method.

Transition from Phononic to Geometrical Mie Modes Measured in Single Subwavelength Polar Dielectric Spheres

Spherical dielectric resonators are highly attractive for light manipulation, thanks to their intrinsic electric and magnetic resonances. Here, we present measurements of the mid-infrared far-field thermal radiation of single subwavelength dielectric spheres deposited on a gold substrate, of radii ranging from 1 to 2.5 μm, which agree quantitatively with simulated absorption cross sections. For SiO2 microspheres, we evidence the excitation of both surface phonon-polariton (SPhP) modes and geometrical electric and magnetic Mie modes. The transition from a phonon-mode-dominated to a Mie-mode-dominated emission spectrum is observed, with a threshold radius of ∼1.5 μm. We also show that the presence of the metallic substrate augments the computed spheres absorption cross-section due to increased local field enhancement, arising from the near-field interaction of the spheres oscillating charges with their image in the metallic mirror. In contrast, measurements of single subwavelength SPhP-inactive PTFE spheres reveal that the mid-infrared response of such lossy spheres is dominated by their bulk absorption. Our results demonstrate how engineering the geometrical and dielectric properties of subwavelength scatterers can enable the control of thermal emission near room temperature, with exciting perspectives for applications such as radiative cooling.

Nonlinear pulse compression to 51-W average power GW-class 35-fs pulses at 2-µm wavelength in a gas-filled multi-pass cell.

We report on the generation of GW-class peak power, 35-fs pulses at 2-µm wavelength with an average power of 51 W at 300-kHz repetition rate. A compact, krypton-filled Herriott-type cavity employing metallic mirrors is used for spectral broadening. This multi-pass compression stage enables the efficient post compression of the pulses emitted by an ultrafast coherently combined thulium-doped fiber laser system. The presented results demonstrate an excellent preservation of the input beam quality in combination with a power transmission as high as 80%. These results show that multi-pass cell based post-compression is an attractive alternative to nonlinear spectral broadening in fibers, which is commonly employed for thulium-doped and other mid-infrared ultrafast laser systems. Particularly, the average power scalability and the potential to achieve few-cycle pulse durations make this scheme highly attractive.

Low-loss fiber grating coupler on thin film lithium niobate platform

A grating coupler with a high coupling efficiency and low back reflections is designed and demonstrated on the thin film lithium niobate platform, which facilitates an efficient interface between a lithium niobate ridge waveguide and a standard single mode fiber. The excellent performances of the present grating coupler are enabled by a cavity-assisted grating structure and a top metal mirror, even though a uniform grating is adopted as the diffractive element. Experimentally, a coupling loss of −0.89 dB at 1552 nm is demonstrated with a 1-dB bandwidth of 45 nm. Low back reflections of &amp;lt;−16.5 dB to the waveguide and &amp;lt;−13.7 dB to the fiber are also achieved from 1536 to 1579 nm.