On-chip complex refractive index detection at multiple wavelengths for selective sensing

Abstract. Modeling the interaction of dust with long-wave (LW) radiation is still a challenge because of the scarcity of information on the complex refractive index of dust from different source regions. In particular, little is known about the variability of the refractive index as a function of the dust mineralogical composition, which depends on the specific emission source, and its size distribution, which is modified during transport. As a consequence, to date, climate models and remote sensing retrievals generally use a spatially invariant and time-constant value for the dust LW refractive index. In this paper, the variability of the mineral dust LW refractive index as a function of its mineralogical composition and size distribution is explored by in situ measurements in a large smog chamber. Mineral dust aerosols were generated from 19 natural soils from 8 regions: northern Africa, the Sahel, eastern Africa and the Middle East, eastern Asia, North and South America, southern Africa, and Australia. Soil samples were selected from a total of 137 available samples in order to represent the diversity of sources from arid and semi-arid areas worldwide and to account for the heterogeneity of the soil composition at the global scale. Aerosol samples generated from soils were re-suspended in the chamber, where their LW extinction spectra (3–15 µm), size distribution, and mineralogical composition were measured. The generated aerosol exhibits a realistic size distribution and mineralogy, including both the sub- and super-micron fractions, and represents in typical atmospheric proportions the main LW-active minerals, such as clays, quartz, and calcite. The complex refractive index of the aerosol is obtained by an optical inversion based upon the measured extinction spectrum and size distribution. Results from the present study show that the imaginary LW refractive index (k) of dust varies greatly both in magnitude and spectral shape from sample to sample, reflecting the differences in particle composition. In the 3–15 µm spectral range, k is between ∼ 0.001 and 0.92. The strength of the dust absorption at ∼ 7 and 11.4 µm depends on the amount of calcite within the samples, while the absorption between 8 and 14 µm is determined by the relative abundance of quartz and clays. The imaginary part (k) is observed to vary both from region to region and for varying sources within the same region. Conversely, for the real part (n), which is in the range 0.84–1.94, values are observed to agree for all dust samples across most of the spectrum within the error bars. This implies that while a constant n can be probably assumed for dust from different sources, a varying k should be used both at the global and the regional scale. A linear relationship between the magnitude of the imaginary refractive index at 7.0, 9.2, and 11.4 µm and the mass concentration of calcite and quartz absorbing at these wavelengths was found. We suggest that this may lead to predictive rules to estimate the LW refractive index of dust in specific bands based on an assumed or predicted mineralogical composition, or conversely, to estimate the dust composition from measurements of the LW extinction at specific wavebands. Based on the results of the present study, we recommend that climate models and remote sensing instruments operating at infrared wavelengths, such as IASI (infrared atmospheric sounder interferometer), use regionally dependent refractive indices rather than generic values. Our observations also suggest that the refractive index of dust in the LW does not change as a result of the loss of coarse particles by gravitational settling, so that constant values of n and k could be assumed close to sources and following transport. The whole dataset of the dust complex refractive indices presented in this paper is made available to the scientific community in the Supplement.

The temperature-induced complex refractive index (CRI) effect of graphene is demonstrated theoretically and experimentally based on a graphene coated in-fiber MZI (Mach–Zehnder interferometer). The relationships between real and imaginary parts of the graphene CRI and temperature are obtained through investigating the dip wavelength and intensity of the MZI interference spectrum changing with temperature, respectively. The temperature effect of CRI of the graphene is also analyzed theoretically. Both experimental and theoretical studies show that the real part and imaginary part of the CRI nonlinearly decrease and increase with temperature increasing, respectively. This graphene-coated in-fiber MZI structure also possesses the advantages of easy fabrication, miniaturization, low cost and robustness. It has potential applications in nanomaterial-based optic devices for communication and sensing.

We analyzed data measured by a Sun-photometer of the RIMA-AERONET network with the purpose to characterize the aerosol properties in the atmosphere over Natal, state capital of Rio Grande do Norte, at the coast of Northeast Brazil. Aerosol Optical Depth, Ångström Exponent, Volume Size Distribution, Single Scattering Albedo, Complex Refractive Index, Asymmetry Factor, and Precipitable Water were analyzed from August 2017 to March 2018. In addition, MODIS and CALIOP observations, local Lidar measurements, and modeled backward trajectories were analyzed in a case study on February 9, 2018, that consistently confirmed the identification of a persistent aerosol layer below 4 km agl. Aerosols present in the atmosphere of Natal showed monthly mean Aerosol Optical Depth at 500 nm below 0.15 (~ 75%), monthly means of the Ångström Exponent at 440-670 nm between 0.30 and 0.70 (~ 69%), bimodal Volume Size Distribution is dominantly coarse mode, Single Scattering Albedo at 440 nm is 0.80, Refractive Index - Real Part around 1.50, Refractive Index - Imaginary Part ranging from 0.01 to 0.04, and the Asymmetry Factor ranged from 0.73 to 0.80. The aerosol typing during the measurement period showed that atmospheric aerosol over Natal is mostly composed of mixed aerosol (58.10%), marine aerosol (34.80%), mineral dust (6.30%), and biomass burning aerosols (0.80%). Backward trajectories identified that 51% of the analyzed air masses over Natal originated from the African continent.

An investigation of the wavelength dependent extinction spectra of coated sphere with different core@shell compositions based on discrete dipole approximation technique has been presented in this paper. We have used combinations of A g, A u, and S i O 2 for this analysis. Specifically, we study the impact of spherical core-shell thickness on its surface plasmon resonance (SPR) peak positions and corresponding spectral widening in distinct regimes of the spectrum. We observe that SPR peak of core-shell nanoparticle(CSNP) can be tuned over the visible to near-infrared spectrum region by manipulating the core/shell ratio and composition of core and shell. Specifically, for dielectric@metal (core@shell) nanoparticle, SPR peak position shifted towards lower wavelength as we increase the shell thickness, which is opposite to the SPR behavior of metal@dielectric. The extinction spectrum shows linear relation between SPR position and thickness of the shell. Further, we observed two resonant peaks for the case of metal@metal CSNP. The SPR peak of Au@Ag (a eff 100 nm with shell thickness 8 nm) reveals two resonant peak corresponding to Au (594 nm) in red domain, while the peak in blue domain corresponds to Ag (402 nm). We also observe that optical resonance of CSNP can be tuned across the near-infrared region by changing the surrounding medium of higher refractive index. Further, near field pattern of core@shell geometry at resonance wavelength is also shown in the present study. We have also compared the numerical and analyticalmethod for smaller size CSNP with varying thickness and the results show good agreement.

High-performance liquid chromatography has already become one of themost widely applied analytical separation techniques because of its superior performance and reliability, especially in the pharmaceutical, environmental, forensic, clinical, food and flavor sciences. However, the relatively slow progress made in the field of HPLC detection has influenced the general progress and the extent of application of HPLC technology. Due to the lack of a universal detector that can be used for quantitative analysis without the need for an authentic standard, the information obtained from analytical HPLC is heavily limited. However, the needs of pharmaceutical companies (e.g. modern drug discovery research using highthroughput quantification methods for lead discovery) and other industries demand the development of a generic quantitative detection technique that can quickly determine the quantity of a chemical without the need to use an authentic standard and the tedious calibration procedure. Researchers are therefore focusing much of their activity into developing a truly “universal” detector for HPLC [1]. The HPLC detectors reported in peer-reviewed publications so far can be classified into [2]: elemental detectors (atomic absorption/emission, inductively coupled plasma–mass spectrometry and microwave-induced plasma); optical detectors (UV/visible, IR/Raman, optical activity, evaporative light scattering and refractive index); luminescent detectors (fluorescence/phosphorescence, chemiluminescence/bioluminescence); electrochemical detectors (potentiometry, novel material/modified electrodes, array electrodes and pulsed and oscillometric techniques); mass spectrometric detectors (time-of-flight/MALDI, Fourier transform ion cyclotron resonance mass spectrometry, electrospray/thermospray, atmospheric pressure ionization and particle beam); and other detection systems (nuclear magnetic resonance, radioactivity detectors, surface plasmon resonance). It is well known that NMR is a spectroscopic techniquewith a very high information content. Although the LC–NMR technique has been successfully applied to the characterization of drug impurities and synthetic compounds in the form of combinatorial libraries [3], analysts are aware of the very high cost of NMR instrumentation. For this reason, the LC–NMR technique has not gained widespread usage [4]. Attention has also focused on the design of LC–FTIR systems, which are either of the flow-cell or the solvent-elimination type. Problems facing this technique include the limited compatibility of the optimized separation and detection conditions, and the rather complicated interface required. Extensive investigations into the use of RI (refractive index) detectors [5–8], evaporative light scattering detectors (ELSDs) [9–12] and chemiluminescence nitrogen detectors (CLNDs) [13–31] as universal detectors for HPLC have been performed. The RI detector, which measures the change in the refractive index of the column effluent as it passes through the flow-cell, could be a universal detector in theory. The greater the difference in RIs between the sample and the mobile phase, the higher the sensitivity of the system. On the other hand, when analyzing complex mixtures, the sample components may cover a wide range of refractive index values, and the RIs of some of the sample components may closely match that of the mobile phase, making them “invisible” to the detector. The RI detector is a pure differential instrument, and any changes in the eluent composition require the rebalancing of the detector. This factor Anal Bioanal Chem (2008) 390:299–301 DOI 10.1007/s00216-007-1633-0

Gradient ion-exchange chromatography (IEC) was interfaced with a low-angle laser light scattering photometer (LALLS) and ultraviolet (UV) and refractive index (RI) detectors connected in series for on-line determination of the differential refractive index (dn/dc) of proteins and eventually their molecular weights (Mw's). Interfacing of gradient HPLC with a RI detector was made possible by using two isorefractive buffers, which helped generate stable baselines for the LALLS and RI detectors. An optically modified, laser based RI detector was used for determination of dn/dc. On-line determinations of dn/dc required smaller amounts of sample compared to off-line determinations (3-4 mg vs 200 mg). Also, dn/dc could be measured by making one repetitive injection of the sample, if the molar absorptivity of the sample was known. dn/dc values determined on-line were in close agreement with those determined off-line. Additionally, percent recovery of the sample was calculated on-line, and this provided true concentration detected at the UV detector, which was then used for determination of Mw.

This article represents an analytical formulation for optical properties of absorbing metallic nanoparticles in visible region of electromagnetic spectrum based on Mie theory, in order to find a clear relationship between fundamental characteristics of nanoparticles with their spectral behavior and color coordinate in CIELAB color space. Calculations were performed on nanoparticles with various diameters (d = 50, 100, and 200 nm), as well as complex refractive index with different real (n = 1.5, 2.0, 2.5, and 3.0) and imaginary (k = 0.001 and 0.1) parts. Obtained results reveal that scattering phenomena in nanoparticles are strongly linked to the particle size parameter and complex index of refraction. The results indicate that the reflectance and lightness (L*) of nanoparticles increases as a result of increase in their size and real part of complex refractive index and decrease with increasing the imaginary part of complex refractive index. The CIELAB colorimetric system was used for analysis the color of nanoparticles. According to obtained results, all nanoparticles have greenish‐blue color, and undergo color change as a result of varying in their size and the complex refractive index. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 477–483, 2016

We report a numerical study of D-shaped photonic crystal fiber based plasmonic refractive index sensor with high resolution and sensitivity in the near-infrared region. D-shaped photonic crystal fiber is formed by side polishing one part of photonic crystal fiber. It has a polishing surface where plasmonic gold layer is coated to modulate the resonant wavelength and enhance the refractive index sensitivity. Several D-shaped photonic crystal fiber plasmonic sensors with various distances from the photonic crystal fiber's core to the polishing surface and gold thicknesses are designed and their characteristics are analyzed by the finite element method. The simulation results indicate that distance from the photonic crystal fiber's core to the polishing surface causes modifications in the loss intensity, the resonant wavelength, and the refractive index sensitivity of D-shaped photonic crystal fiber plasmonic sensor. Mass production of refractive index sensors were achieved using a simple fabrication process, whereby the D-shaped photonic crystal fiber is grinded where distance from the photonic crystal fiber's core to the polishing surface is less than one layer thickness and then coated with the gold layer. For the refractive index sensing applications, the maxima theoretical resolution and sensitivity of D-shaped photonic crystal fiber plasmonic sensor reach 2.98 × 10 6refractive index unit and 6,140 nm/refractive index unit in range of 1.30-1.37, respectively. We also report an initial fabrication of the D-shaped photonic crystal fiber following the standard stack-and- draw method to demonstrate the feasibility of the proposed device by using our in-house equipments. The proposed D-shaped photonic crystal fiber plasmonic sensor design in this work would be useful for the development of cheap refractive index sensors with high sensitivity and resolution.

The advantage of the study is that nonlinear behavior of light inside ring resonators system can be controlled and managed by using appropriate parameters of the microring resonator (MRR) system. The effects of the coupling coefficients on the bifurcation and chaos behaviors, in terms of roundtrip and output powers are presented. Moreover, the radius of the ring is the key parameter which causes the nonlinear behaviors happen in lower roundtrips. Input optical powers can be in the form of an optical dark/bright soliton or a Gaussian beam. Optical soliton can be used to generate chaotic filter characteristics when propagating within the single microring resonator (SMRR). Therefore, chaotic signals are generated, whereas the required signals including specific wavelengths or frequencies can be used to perform the optical communication. The wide range of spread wavelength can be generated, using proposed MRRs system, where the wavelength multiplexing, dense wavelength division multiplexing (DWDM) can be perform via the optical wireless communication. The proposed MRR systems are suitable for the multi soliton pulses generation, which are available for high performance communication network. Increasing in communication capacity is provided by increasing of soliton pulses, which can be performed by generation of temporal and spatial optical soliton pulses. Generated multi optical soliton can be input into an optical receiver unit which is a quantum processing system used to generate high capacity packet of quantum information within the series of MRRs.

A multiscale nonreciprocal thermal radiation multilayer structure based on Weyl semimetal with angle and refractive index detection

A surface plasmon resonance sensor based on microstructured fiber (MSF) is proposed for low refractive index (RI) detection in the range of 1.20–1.34. The MSF is composed of substrate and sector air rings with negative curvature. Gold is coated on the external cladding surface. A finite element method is applied to analyze the performance of the sensor. Results show that the sensor is independent of polarization, and the resonance wavelength has a negative shift with RI variation in the near-infrared (near-IR) spectrum. The average sensitivity is $ - 8892\,\,{\rm nm/RIU}$−8892nm/RIU, and the maximum resolution is ${6.54} \times {{10}^{ - 6}}$6.54×10−6. Owing to the high sensitivity in the low RI range, the sensor offers a promising approach for water pollution measuring, humidity monitoring, and liquid concentration testing.

Vacuum birefringence in strong magnetic fields: (II) Complex refractive index from the lowest Landau level

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTHigh-Q Optical Sensors for Chemical and Biological AnalysisMatthew S. Luchansky and Ryan C. Bailey*View Author Information Department of Chemistry, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States*E-mail: [email protected]. Address: 44 Roger Adams Lab 600 South Mathews Avenue, Urbana, IL, 61801. Phone: (217) 333-0676.Cite this: Anal. Chem. 2012, 84, 2, 793–821Publication Date (Web):November 23, 2011Publication History Published online23 November 2011Published inissue 17 January 2012https://pubs.acs.org/doi/10.1021/ac2029024https://doi.org/10.1021/ac2029024review-articleACS PublicationsCopyright © 2011 American Chemical SocietyRequest reuse permissionsArticle Views6236Altmetric-Citations223LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Assays,Crystals,Nanoparticles,Quantum mechanics,Sensors Get e-Alerts

This paper presents the application of a theoretically developed method that provides plasma parameter solution space information from measured RF attenuation that occurs during reentry. The purpose is to provide reentry plasma parameter information from the communication signal attenuation. The theoretical development centers around the attenuation and the complex index of refraction. The methodology uses an imaginary index of the refraction matching algorithm with a tolerance to find suitable solutions that satisfy the theory. The imaginary matching terms are then used to determine the real index of refraction resulting in the complex index of refraction. Then a filter is used to reject nonphysical solutions. Signal attenuation-based plasma parameter properties investigated include the complex index of refraction, plasma frequency, electron density, collision frequency, propagation constant, attenuation constant, phase constant, complex plasma conductivity, and electron mobility. RF plasma thickness attenuation is investigated and compared to the literature. Similar plasma thickness for a specific signal attenuation can have different plasma properties.

Combining a transfer matrix analysis and slowly varying envelope approximation, we propose a simple method to describe steady states associated with dispersive multistability in coupled microring resonators. This approach allows us to consider nonlinear interactions between independent forward and backward propagative fields. We applied this simple formalism first to decrease the tristability intensity threshold in linearly coupled resonators and second to optically control the tristable behavior in a single microring resonator.