Miniaturized infrared spectrometer based on the tunable graphene plasmonic filter.

Miniaturization of a conventional spectrometer is challenging because of the tradeoffs of size, cost, signal-to-noise ratio, and spectral resolution, etc. Here, a new type of miniaturized infrared spectrometer based on the integration of tunable graphene plasmonic filters and infrared detectors is proposed. The transmittance spectrum of a graphene plasmonic filter can be tuned by varying the Fermi energy of the graphene, allowing light incident on the graphene plasmonic filter to be dynamically modulated in a way that encodes its spectral information in the receiving infrared detector. The incident spectrum can then be reconstructed by using decoding algorithms such as ridge regression and neural networks. The factors that influence spectrometer performance are investigated in detail. It is found that the graphene carrier mobility and the signal-to-noise ratio are two key parameters in determining the resolution and precision of the spectrum reconstruction. The mechanism behind our observations can be well understood in the framework of the Wiener deconvolution theory. Moreover, a hybrid decoding (or recovery) algorithm that combines ridge regression and a neural network is proposed that demonstrates a better spectral recovery performance than either the ridge regression or a deep neural network alone, being able to achieve a sub-hundred nanometer spectral resolution across the 8∼14 µm wavelength range. The size of the proposed spectrometer is comparable to a microchip and has the potential to be integrated within portable devices for infrared spectral imaging applications.

Impact of the pitch angle on the spin Hall effect of light weak measurement.

The spin Hall effect of light (SHEL), as a photonic analogue of the spin Hall effect, has been widely studied for manipulating spin-polarized photons and precision metrology. In this work, a physical model is established to reveal the impact of the interface pitch angle on the SHEL accompanied by the Imbert-Fedorov angular shift simultaneously. Then, a modified weak measurement technique is proposed in this case to amplify the spin shift experimentally, and the results agree well with the theoretical prediction. Interestingly, the amplified transverse shift is quite sensitive to the variation of the interface pitch angle, and the performance provides a simple and effective method for precise pitch angle sensing with a minimum observable angle of 6.6 × 10-5°.

[Research progress in sample pretreatment and analytical techniques for cosmetics].

With the continuous economic development and improvement of living standards, cosmetic products are being widely used as daily consumer products, and there are increasing concerns about their safety. Consequently, there is a substantial increase in the number of cosmetic samples subjected to various analyses, and this in turn necessitates more stringent requirements for the related analytical techniques. However, traditional sample pretreatment and analytical techniques are time-consuming, require large amounts of organic solvents, and have low throughput, thus failing to meet the current demand for green analytical chemistry. To address this issue, researchers have developed numerous environmentally friendly pretreatment techniques as well as high-throughput and rapid on-site methods to ensure the quality and safety of cosmetics. This paper reviews the current progress in sample pretreatment and analytical techniques for cosmetics and discusses the trends and prospects, which may provide technical guidance for researchers and inspectors in the analysis of cosmetic products.

Ultrahigh Frequency and Anti-Interference Optical-Mode Resonance with Biquadratic Coupled FeCoB/Ru/FeCoB Trilayers.

Microwave soft magnetic films (SMFs) are the key materials to effectively miniaturize and multifunctionalize the microwave electromagnetic components and devices. However, currently, single-layer SMFs encounter a frequency bottleneck at around 10 GHz. The ferromagnet/nonmagnetic spacer/ferromagnet sandwiched films with strong interlayer exchange coupling are possible solutions to break through that frequency limitation because they exhibit ultrahigh optical-mode (OM) resonance frequency frO up to 50 GHz, while the tiny permeability and the limited thickness are their own obstacles to overcome. In this study, biquadratic coupled FeCoB25nm/Ru0.25nm/FeCoB25nm sandwiched films with uniaxial magnetic anisotropy were deposited by a composition gradient sputtering method. Pure OM resonance with self-bias frO up to 18.21 GHz and a relative permeability µrO as high as 169 at the cut-off frequency was achieved. Moreover, both the frO and µrO remain unchanged in the magnetic field range of 0-80 Oe, indicating a strong anti-interference capability to small interference field. These results demonstrate that the biquadratic coupled OM resonance can solve the current frequency bottleneck of microwave SMFs by providing ultrahigh resonance frequency while maintaining considerable permeability, thus leading to potential applications of OM resonance in Ku-band microwave magnetic components.

High efficiency active wavefront manipulation of spin photonics based on a graphene metasurface.

Metasurfaces have been widely studied for manipulating light fields. In this work, a novel metasurface element is achieved with a high circular polarization amplitude conversion efficiency of 88.5% that creates an opposite phase shift ranging from -180° to 180° between incidence and reflection for different spin components. By arranging the elements according to different requirements, spin-dependent reflection, focusing and scattering are demonstrated. It is also demonstrated that tuning of the Fermi energy is an viable way to active control the circular polarization conversion efficiency and expand the applicable bandwidth. The results open a new route for modifying and designing the wavefront of circular polarized light.

Stress-Enhanced Interlayer Exchange Coupling and Optical-Mode FMR Frequency in Self-Bias FeCoB/Ru/FeCoB Trilayers.

Nowadays, the most popular method to increase ferromagnetic resonance (FMR) frequency ( fr) in self-bias soft magnetic films is to improve the anisotropy field HK. However, to push fr to higher frequencies only via raising HK becomes increasingly challenging because fr is already higher than 10 GHz by now. In this study, we fabricated a series of magnetically anisotropic FeCoB/Ru/FeCoB sandwich films possessing antiferromagnetic-like coupling and gradually increased uniaxial stress in the FeCoB sublayers from 52 to 110 MPa. It is quite remarkable that the acoustic mode of FMR gradually disappears, whereas the optical mode is enhanced in these structures. We observed simultaneous enhancement of HK and interlayer coupling field ( JIEC) with the uniaxial stress, which leads to a very pronounced optical-mode frequency increase from 8.67 to 11.62 GHz with a very sensitive stress response of 51 Hz/Pa. In contrast, the fr in a FeCoB single layer (acoustic mode) only varies from 3.47 to 5.05 GHz under similar stress. We believe that the strain-induced electron density variation of the Ru spacer's Fermi surface in the out-of-plane direction is responsible for the enhancement of JIEC. This study demonstrates that the antiferromagnetic coupling is a new route to achieve higher fr and provides the possibility of engineering and manipulating optical-mode resonance simply by controlling the interlayer coupling strength via stress.

Tunable spin Hall effect of light with graphene at a telecommunication wavelength.

The spin Hall effect of light (SHEL) has been widely studied for manipulating spin-polarized photons. In this Letter, we present a mechanism to tune the spin shift of the SHEL electrically at 1550 nm by means of introducing a graphene layer. The spin shift is quite sensitive to a graphene layer near the Brewster angle for horizontal polarization incidence and can be dynamically tuned by varying the Fermi energy of graphene. We find that the position of the Brewster angle and the value of the spin shift are decided by the real and imaginary parts of graphene conductivity, respectively. In addition, two different tuned regions have been revealed: one is the "step-like switch" region where the spin shift switches between two values, and the other is the "negative modulation" region where the spin shift declines gradually as the Fermi energy increases. These findings may provide a new paradigm for a tunable spin photonic device.

Laboratory simulation of laser propagation through plasma sheaths containing ablation particles of ZrB2-SiC-C during hypersonic flight.

The optical communication method has potential for solving the blackout problem, which is a big challenge faced in the development of aerospace. Two laser transmission systems were set up to explore the influence of the plasma and the ablation particles on the propagation of the laser. The experimental results indicate that the laser can transmit through the plasma with little attenuation. When there are ablation particles of ZrB2-SiC-C added in the plasma, the intensity of the laser has fluctuations. The work introduced in this Letter can be regarded as basic research of the propagation characters of the laser through plasma sheaths.

[Rapid screening of three halogenated salicylanilines in cosmetics using ambient ionization coupled with ion mobility spectrometry].

OBJECTIVE: A rapid analytical method had been developed for the screening of three halogenated salicylanilines in cosmetics using ambition ionization coupled with ion mobility spectrometry. METHODS: Without time-consuming pretreatment, cosmetic samples of lotion, lipstick and powder were added or smudged onto a Grade 3MM chromatography paper for paper spray ionization, cosmetic samples of cream and shampoo were simply loaded with a metal wire probe for extraction nano-electrospray. RESULTS: The limits of detection( LODs) for the three halogenated salicylanilides were 50 µg/kg. The instrumental analysis time for a single ion mobility spectrometry run was less than 15 ms. The suspected positive samples were subjected to further verification by high-performance liquid chromatography coupled with tandem mass spectrometry. CONCLUSION: The method is simple, rapid, and with low cost and is suitable for rapid, on-site screening of cosmetics.

[Determination of six allergenic coumarin compounds in children's toys using hollow-fiber liquid-phase microextraction followed by ultra-performance liquid chromatography-tandem mass spectrometry].

A comprehensive analytical method was developed for the determination of six allergenic coumarin compounds (coumarin, 7-methyl coumarin, 7-methoxycoumarin, 7-ethoxy-4-methyl coumarin, 4,6-dimethyl-8-tert-butyl coumarin and hexahydrocoumarin) in children's toys based on hollow-fiber liquid-phase microextraction (HF-LPME) followed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). HF-LPME was employed in sample pretreatment with the following parameters:extraction solvent of n-octanol, stirring rate of 700 r/min, extraction time of 50 min and amount of sodium chloride of 0.7 g. After chromatographic separation on an ACQUITY UPLC BEH Phenyl column (150 mm×2.1 mm, 1.7 µm), the target compounds were analyzed under multiple reaction monitoring (MRM) mode in positive electrospray ionization mode. The limits of quantification (LOQs) of the six allergenic coumarin compounds were either 2 µg/kg (7-ethoxy-4-methyl coumarin and 4,6-dimethyl-8-tert-butyl coumarin) or 10 µg/kg (coumarin, hexahydrocoumarin, 7-methyl coumarin and 7-methoxycoumarin). The average recoveries at different spiked levels ranged from 70.8% to 118.9% with relative standard deviations (RSDs) of 0.19%-16.34% (n=6). The proposed method is accurate, sensitive, reliable, and can be applied for the inspection and quality control of toy products.

Engineering optical mode ferromagnetic resonance in FeCoB films with ultrathin Ru insertion.

Ferromagnetic resonance (FMR) in soft magnetic films (SMFs) to a large extent determines the maximum working frequency of magnetic devices. The FMR frequency (fr) in an optical mode is usually much higher than that in the corresponding acoustic mode for exchange coupled ferromagnet/nonmagnet/ferromagnet (FM/NM/FM) trilayers. In this study, we prepared a 50 nm FeCoB film with uniaxial magnetic anisotropy (UMA), showing a high acoustic mode fr of 4.17 GHz. When an ultrathin Ru spacer was inserted in the very middle of the UMA-FeCoB film, the zero-field FMR was abruptly switched from an acoustic mode to an optical one with fr dramatically enhanced from 4.17 GHz to 11.32 GHz. Furthermore, the FMR mode can be readily tuned to optical mode only, acoustic mode only, or double mode by simply varying the applied filed, which provides a flexible way to design multi-band microwave devices.

Driving ferromagnetic resonance frequency of FeCoB/PZN-PT multiferroic heterostructures to Ku-band via two-step climbing: composition gradient sputtering and magnetoelectric coupling.

RF/microwave soft magnetic films (SMFs) are key materials for miniaturization and multifunctionalization of monolithic microwave integrated circuits (MMICs) and their components, which demand that the SMFs should have higher self-bias ferromagnetic resonance frequency fFMR, and can be fabricated in an IC compatible process. However, self-biased metallic SMFs working at X-band or higher frequency were rarely reported, even though there are urgent demands. In this paper, we report an IC compatible process with two-step superposition to prepare SMFs, where the FeCoB SMFs were deposited on (011) lead zinc niobate-lead titanate substrates using a composition gradient sputtering method. As a result, a giant magnetic anisotropy field of 1498 Oe, 1-2 orders of magnitude larger than that by conventional magnetic annealing method, and an ultrahigh fFMR of up to 12.96 GHz reaching Ku-band, were obtained at zero magnetic bias field in the as-deposited films. These ultrahigh microwave performances can be attributed to the superposition of two effects: uniaxial stress induced by composition gradient and magnetoelectric coupling. This two-step superposition method paves a way for SMFs to surpass X-band by two-step or multi-step, where a variety of magnetic anisotropy field enhancing methods can be cumulated together to get higher ferromagnetic resonance frequency.

General conformal transformation method based on Schwarz-Christoffel approach.

A general conformal transformation method (CTM) is proposed to construct the conformal mapping between two irregular geometries. In order to find the material parameters corresponding to the conformal transformation between two irregular geometries, two polygons are utilized to approximate the two irregular geometries, and an intermediate geometry is used to connect the mapping relations between the two polygons. Based on these manipulations, the approximate material parameters for TE and TM waves are finally obtained by calculating the Schwarz-Christoffel (SC) mappings. To demonstrate the validity of the method, a phase modulator and a plane focal surface Luneburg lens are designed and simulated by the finite element method. The results show that the conformal transformation can be expanded to the cases that the transformed objects are with irregular geometries.

Artificial metal with effective plasma frequency in near-infrared region.

We have proposed and demonstrated an artificial medium consisting of arrays of circular metal rods embedded in a dielectric host, which holds a real metal behavior but the extracted effective plasma frequency is in near-infrared region. The electromagnetic responses of such medium and the retrieved effective material parameters have been particularly shown. In addition, an analytic model about effective plasma frequency is constructed by uniquely considering the skin effect and introducing the parameter-skin depth, whose predicting results are in well accordance with the FDTD simulation. This artificial material may open possibilities for many metal-based applications in near-infrared regime.

A design method to change the effective shape of scattering cross section for PEC objects based on transformation optics.

A design method was proposed for transforming the scattering cross section's shape of PEC objects to other arbitrary shapes based on transformation optics. The parameters of the transformer which is a kind of metamaterial being tightly covered to the original PEC object can be determined by the transformation expressions derived in the paper. With the method, the virtual PEC objects with their definite shape of the scattering cross section can be produced visually through the original PEC objects with a designed transformer. The validation was made by comparing the distribution of electromagnetic field of the PEC objects with and without transformer by means of finite-element method. Some examples are also given for demonstrating the effectiveness of the method.