Particle Refractive Index Research Articles

Unambiguous derivation of the effective refractive index of biological suspensions and an extension to dense tissue such as blood.

The van de Hulst formula provides an expression for the effective refractive index or effective propagation constant of a suspension of particles of arbitrary shape, size, and refractive index in an optically homogeneous medium. However, its validity for biological matter, which often consists of very dense suspensions of cells, is unclear because existing derivations of the formula or similar results rely on far-field scattering and/or on the suspension in question being dilute. We present a derivation of the van de Hulst formula valid for suspensions of large, tenuous scatterers-the type biological suspensions are typically made of-that does not rely on these conditions, showing that they are not strictly necessary for the formula to be valid. We apply these results specifically to blood and epithelial tissue. Furthermore, we determine the true condition for the formula to be valid for these types of tissues. We finally provide a simple way to estimate-and, more importantly, correct-the error incurred by the van de Hulst formula when this condition is not met.

Twin curvilinear vortex beams.

We report on a novel curvilinear optical vortex beam named twin curvilinear vortex beams (TCVBs) with intensity and phase distribution along a pair of two- or three-dimensional curves, both of which share the same shape and the same topological charge. The TCVBs also possess the character of perfect optical vortex, namely having a size independent of topological charge. We theoretically demonstrate that a TCVB rather than a single-curve vortex beam can be created by the Fourier transform of a cylindrically polarized beam. The behavior of TCVBs generated through our method is investigated by simulation and experiment, including interference experiments for identifying the vortex property of the TCVBs. The TCVBs may find applications in optical tweezers, such as trapping low refractive index particles in the dark region between two curves and driving them moving along the curvilinear trajectory.

Measurement of particle size and refractive index based on interferometric particle imaging

The interferometric particle imaging (IPI) technique makes use of the angular oscillations of scattered light for droplet or bubble sizing. The out-of-focus image of the scattered light consists of fringes, the spacing of which reflects the interference between the surface-reflected light and the first-order refracted light. In this work, a method is presented for measuring both the refractive index and the size of a particle simultaneously with the IPI technique which employs two CCD cameras located at different scattering angles in the forward direction. The refractive index is evaluated by comparing the fringe spacings of the interferogram images and the particle diameter is extracted from either of the interferogram images with a combination of the measured refractive index. The method is validated by the measurements of water droplet and glycerol droplet suspended in air.A method is presented for measuring both the refractive index and the size of a particle simultaneously with the IPI technique which employs two CCD cameras located at different scattering angles in the forward direction. The refractive index is evaluated by comparing the fringe spacings of the interferogram images and the particle diameter is extracted from either of the interferogram images with a combination of the measured refractive index. The method is validated by the measurements of water droplet and glycerol droplet suspended in air.

Analytical Jacobians of single scattering optical properties using the invariant imbedding T-matrix method

Integrated and differential optical properties of a single particle, such as the scattering, absorption, and extinction cross sections, single scattering albedo, asymmetry factor, and scattering phase matrix, are derived from electromagnetic scattering theory. This process depends on microphysical inputs which include particle shape, refractive index, aspect ratio, and size parameter. In this work, we use the invariant imbedding T-matrix method (IITM) to derive analytic expressions for Jacobians of these optical properties with respect to the input parameters. These IITM-derived Jacobians for spheroids, cylinders, and hexagonal prisms are validated by comparison with results calculated with the extended boundary condition method (EBCM) and further validated using finite-difference estimates. We examine the dependencies of these Jacobians as functions of the input microphysical parameters, focusing again on spheroids, cylinders, and hexagonal prisms.

Computational investigation of the plasmonic properties of TiN, ZrN, and HfN nanoparticles: the role of particle size, medium, and surface oxidation

Group 4 transition metal nitride (TMN) nanoparticles (NPs) display strong plasmonic responses in the visible and near-infrared regimes, exhibit high melting points and significant chemical stability, and thus are potential earth-abundant alternatives to Au and Ag based plasmonic applications. However, a detailed understanding of the relationship between TMN NP physical properties and plasmonic response is required to maximize their utility. In this study, the localized surface plasmon resonance (LSPR) frequency, bandwidth, and extinction of titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) NPs were examined as a function of the particle size, surface oxidation, and refractive index of the surrounding medium using finite element method (FEM). A linear redshift in the LSPR frequency and a linear increase in the associated full width at half maximum (FWHM) was observed with increasing the particle size, oxidation layer thickness, and medium refractive index. We show that the effect of surface oxidation on plasmonic properties of TMN NPs is strongly size-dependent with a significant LSPR redshift, intensity reduction, and broadening in small NPs compared with larger NPs. Furthermore, the performance and efficiency of HfN, ZrN, and TiN, as well as Au NPs for narrowband (photothermal therapy, PTT) and broadband (solar energy conversion) applications, was investigated in detail. The results indicate that narrowband and broadband photothermal performance of NPs strongly depend on the particle size, surface properties, and in case of narrowband absorption, excitation wavelength.

Trapping two types of Rayleigh particles simultaneously by a focused rotational elliptical Laguerre–Gaussian correlated Schell-model beam

We analyze the optical radiation forces, produced by a focused rotational elliptical Laguerre–Gaussian correlated Schell-model (ELGSM) beam, on the dielectric particles of different refractive indices in the Rayleigh scattering regime. It is found that through a judicious modulation of the initial spatial coherence width and the beam order of the correlation function of the rotational ELGSM beam, the particles with higher refractive index (compared with the ambient) can be trapped along an elliptical ring centered at the focus, the particles with lower refractive index, at the same time, will be trapped at the focal point. Our results also show that the trapping area/range can be modulated by structuring the correlation function of the beam. By comparing the gradient, scattering, Brownian, and gravity forces acting on the particles, the trapping stability is analyzed. Our results indicate that the coherence structure engineering can be used as an alternative approach to modulate the symmetry of the optical trapping area.

CCRD based development of bromocriptine and glutathione nanoemulsion tailored ultrasonically for the combined anti-parkinson effect

Bromocriptine Mesylate (BRM) acts as a dopamine receptor agonist along with antioxidant effect and is utilized in the treatment of Parkinson’s disease (PD). Glutathione (GSH) is a thiol- reducing agent having antioxidant properties in the brain. Replenishment of GSH inside the brain can play a major role in the management of PD. Both BRM and GSH suffer from low oral bioavailability and poor absorption. The objective of the present study was to develop BRM and GSH loaded nanoemulsion for the combined and synergistic effect delivered through the intranasal route for the better and effective management of PD. After extensive screening experiments, Capmul PG-8 NF was selected as oil, polyethylene glycol (PEG) 400 as a surfactant and propylene glycol as co-surfactant. Ultrasonication technique was employed for the fabrication of nanoemulsion. Central composite rotatable design (CCRD) was used to obtain the best formulation by optimization. Oil (%), Smix (%), and sonication time (second) were chosen as independent variables for the optimization. Particle size, PDI, zeta potential, % transmittance, pH, refractive index, viscosity and conductivity of the optimized nanoemulsion were found to be 80.71 ± 2.75 nm, 0.217 ± 0.009, −12.60 ± 0.10 mV, 96.00 ± 3.05 %, 6.48 ± 0.28, 1.36 ± 0.03, 30.12 ± 0.10 mPas and 214.28 ± 2.79 μS/cm respectively. Surface morphology demonstrated that nanoemulsion possessed spherical and globular nature of the particle which showed 3.4 times and 1.5 times enhancement in drug permeation in the case of BRM and GSH respectively as compared to suspension. MTT assay done on neuro-2a cell lines revealed that nanoemulsion was safe for intranasal delivery. Behavioural studies were carried out to prove the efficacy of optimized nanoemulsion in PD using forced swimming test, locomotor activity test, catalepsy test, rota-rod test, and akinesia test in Wistar rats. The outcomes of the behavioural studies revealed that BRM and GSH loaded nanoemulsion treatment showed significant improvement in behavioural activities of PD (haloperidol-induced) rats after intranasal administration. This study concluded that BRM and GSH loaded nanoemulsion could be promising for the combined and synergistic anti-parkinson effect for the effective management of PD.

Particle Size and Refractive Index Measurement Based on the Polarization Distribution Difference of Scattered Light

Particle Size and Refractive Index Measurement Based on the Polarization Distribution Difference of Scattered Light

An experimental method of simultaneously studying refractive index and dynamic properties of transparent materials

Based on the electromagnetic loading device CQ-4, an experimental method of simultaneously measuring the refractive index and high pressure sound velocity of transparent material is established. The ramp wave compression experiment of PMMA is carried out under a pressure of 14 GPa. The velocity history curves of PMMA sample rear surface are obtained by dual laser heterodyne velocimetry (DLHV). The velocity curve shows obvious double wave structure, which indicates the elastic-plastic transition. The refractive index particle velocity optical characteristics and Lagrangian sound velocity particle velocity dynamic characteristics of PMMA are obtained simultaneously with the experimental data processing.

Optical Trapping Raman Spectroscopy As a Sensor / Actuator / Treatment System

In recent years, Raman spectroscopy has evolved into a broadly used analytical method in chemistry, life sciences, and medicine. Here, we combine Raman spectroscopy with optical trapping and optical microscopy to isolate and investigate individual micron-size biological particles from a sample. In this setup, Raman spectroscopy provides a label-free chemical fingerprint while light microscopy reveals the sample morphology. In addition, elastic light scattering as well as observation of diffusive movement in the optical trap’s potential offer information on particle size and refractive index. Single particles can be captured and manipulated for tens of minutes. During this time, the stably trapped particles can be exposed to a variety of chemical and physical stimuli such as heat, light of different wavelengths, or changes in the chemical composition of the particle environment through microfluidics (Fig. 1A).In this work, we employ this optical trapping Raman spectroscopy sensor / actuator / treatment system to study the effect of hydrogen peroxide (H2O2) on individual spores of Bacillus atrophaeus, an important model system to assess the efficacy of industrial sterilization processes. Interestingly, we find B. atrophaeus spores to be stable for more than 30 minutes while optically trapped even at elevated temperatures (> 70 °C). Exposure to H2O2 results in spore degradation in a concentration-dependent manner within several minutes and is accelerated by high temperatures. Raman spectroscopy indicates that spore degradation is characterized by the rupture of the spore core resulting in the fast release of dipicolinic acid, a major spore biomarker that is considered key for spore resistance to environmental stress (Fig. 1B). Oxidative degradation of the spore shell starts before core rupture and continues after dipicolinic acid release. Simultaneous observation of spore morphology corroborates this two-phase model. Illumination with shorter (< 550 nm) wavelength light exposes the spores to oxidative stress via the generation of reactive oxygen species in the spore environment by light, thereby mimicking the H2O2 sterilization process. In the presence of small amounts (0.5%) H2O2, spore lifetime is reduced to several seconds.With the presented system, we address spore activity down to the single cellular level in a multimodal manner: trapping and manipulation of single spores over several tens of minutes (actuator functionality), stimulation of single spores by temperature, illumination, and H2O2 exposure (treatment functionality) as well as on-line monitoring of spore activity (sensor functionality). Figure 1

Spaceborne Middle‐ and Far‐Infrared Observations Improving Nighttime Ice Cloud Property Retrievals

AbstractTwo upcoming missions are scheduled to provide novel spaceborne observations of upwelling far‐infrared spectra. In this study, the accuracy of ice cloud property retrievals using spaceborne middle‐to‐far‐infrared (MIR‐FIR) measurements is examined toward a better understanding of retrieval biases and uncertainties. Theoretical sensitivity studies demonstrate that the MIR‐FIR spectra are sensitive to ice cloud properties, thereby providing a robust means for retrieving cloud properties under nighttime conditions. However, the temperature dependence of the ice refractive index and relevant ice particle shape models need to be incorporated into the retrieval procedure to avoid systematic biases in inferring cloud optical thickness and effective particle radius. Furthermore, prior information of subpixel cloud fractions is essential to mitigation of substantial systematic retrieval biases due to inconsistent subpixel cloud fractions.

An experimental study on light scattering matrices for Chinese loess dust with different particle size distributions

Abstract. Mineral dust suspended in the atmosphere has significant effects on radiative balance and climate change. The Chinese Loess Plateau (CLP) is generally considered one of the main sources of Asian dust aerosol. After being lifted by wind, dust particles with various size distributions can be transported over different distances. In this study, an original loess sample was collected from Luochuan, which is centrally located on the CLP, and two samples with different size distributions were obtained afterwards. “Pristine loess” was used to represent dust that only affects source regions, part of pristine loess was milled to finer “milled loess” that can be transported over long distances. Light scattering matrices for these two samples were measured at 532 nm wavelength from 5 to 175∘ angles. Particle size distribution, refractive index, chemical component, and microscopic appearance were also characterized for auxiliary analyses. Experimental results showed that there are obvious discrepancies in angular behaviors of matrix elements for pristine loess and milled loess, and these discrepancies are different from those for other kinds of dust with distinct size distributions. Given that the effective radii of these two loess samples differ by more than 20 times, it is reasonable to conclude that the difference in size distributions plays a major role in leading to different matrices, while differences in refractive index and microstructure have relatively small contributions. Qualitative analyses of numerical simulation results of irregular particles also validate this conclusion. Gaussian spheres may be promising morphological models for simulating the scattering matrix of loess but need further quantitative verification. Finally, synthetic scattering matrices for both pristine loess and milled loess were constructed over 0–180∘, and the previous average scattering matrix for loess dust was updated. This study presents measurement results of Chinese loess dust and an updated average scattering matrix for loess, which are useful for validating existing models, developing more advanced models for optical simulations of loess dust, and helping to improve retrieval accuracy of dust aerosol properties over both source and downwind areas.

Thermosensitive Brinzolamide in situ Gel Nanoemulsions, in vitro and ex vivo Evaluation

Brinzolamide (BZ) is a carbonic anhydrase inhibitor with selectivity and affinity for the carbonic anhydrase type II isoenzyme that administrated topically as an ophthalmic suspension for reducing intraocular pressure. In this study, BZ in situ gel nanoemulsions (NEs) were developed and evaluated for transcorneal permeation via the bovine corneal membrane. The spontaneous emulsification method was employed to prepare BZ in situ gel NEs. Various physicochemical characteristics, including particle size, polydispersity index, pH, refractive index, and viscosity, were evaluated. Accelerated physical stability and in vitro drug release, as well as transcorneal permeation studies was performed by applying the Franz-type diffusion cells. Thermosensitive BZ in situ gel NEs with desired physicochemical features and sustained release profiles were designed in the current study. Optimized Formulations exhibited physical stability under different conditions. The transcorneal permeation of formulations was higher than that of suspension, especially for F3b formulation. According to the present in vitro and ex vivo evaluations, it is concluded that in situ gel NEs could be a topical administration of BZ as a suitable ocular drug delivery system.

Shifts in Phytoplankton Community Structure Across an Anticyclonic Eddy Revealed From High Spectral Resolution Lidar Scattering Measurements

Changes in airborne high spectral resolution lidar (HSRL) measurements of scattering, depolarization, and attenuation coincided with a shift in phytoplankton community composition across an anticyclonic eddy in the North Atlantic. We normalized the total depolarization ratio (delta) by the particulate backscattering coefficient (b(b)(p)) to account for the covariance in delta and b(b)(p) that has been attributed to multiple scattering. A 15% increase in delta/b(b)(p) inside the eddy coincided with decreased phytoplankton biomass and a shift to smaller and more elongated phytoplankton cells. Taxonomic changes (reduced dinoflagellate relative abundance inside the eddy) were also observed. The delta signal is thus potentially most sensitive to changes in phytoplankton shape because neither the observed change in the particle size distribution (PSD) nor refractive index (assuming average refractive indices) are consistent with previous theoretical modeling results. We additionally calculated chlorophyll-a (Chl) concentrations from measurements of the diffuse light attenuation coefficient (K-d) and divided by b(b)(p) to evaluate another optical metric of phytoplankton community composition (Chl:b(bp)), which decreased by more than a factor of two inside the eddy. This case study demonstrates that the HSRL is able to detect changes in phytoplankton community composition. High spectral resolution lidar measurements reveal complex structures in both the vertical and horizontal distribution of phytoplankton in the mixed layer providing a valuable new tool to support other remote sensing techniques for studying mixed layer dynamics. Our results identify fronts at the periphery of mesoscale eddies as locations of abrupt changes in near-surface optical properties.

Effects of environment variation of glycerol smoke particles on the persistence of linear and circular polarization.

Environment variation is an important factor affecting the polarization propagation through the smoke. In this paper, we investigate the effects of the relative humidity and optical thickness on polarization transmission character, as well as the persistence of the linear and circular polarization of artificial smoke particles with simulations and experiments. We develop an environment modulation system to control the environment variation and measure the transmission degree of polarization (DOP). Correspondingly, by building the relation between the smoke filling time and optical thickness, as well as between the relative humidity and particle size and refractive index, we utilize the Monte Carlo program to track photon scattering process through varying the radius, refractive index and optical thickness. Both the simulation and the experimental results show that the DOP of both linear and circular polarizations are constantly decreased with the increasing of the optical thickness. However, at the same optical thickness, both the linear and circular polarization's persistence benefits with the increasing of the relative humidity. Moreover, circular polarization persists better than linear polarization in the larger optical thickness and the higher humidity environment under the wavelength of 532 nm. These works can verify the persistence of circular polarization and broaden the application range of polarized lights in a variable artificial smoke environment.

Miniature particulate matter counter and analyzer based on lens-free imaging of light scattering signatures with a holed image sensor

We report our latest developments on a novel miniature particulate matter (PM) sensor for personal air quality monitoring. This optical sensor combines a visible fibered light source and a vertical air channel drilled out of a holed retina. The fabrication of such retina features an unconventional design of a CMOS image sensor and a specific drilling post process at wafer level. The scattering of light by a single particle generates a distinctive pattern. By using a compact optical set-up, we measure a lens-free projection of the scattering signature on the image sensor. We present the design and fabrication of such sensor as well as experimental signatures that are consistent with our in-house analytical model. We demonstrate counting and differentiation between calibrated particles of different sizes. Our current setup allows for the detection of single 320 nm polystyrene particles. Finally, we describe our image analysis procedure that fits a measured signature with a modelled one in order to retrieve particle's size and refractive index.

Spectrally dependent linear depolarization and lidar ratios for nonspherical smoke aerosols

We use the numerically exact T-matrix method to model light scattering and absorption by aged smoke aerosols at lidar wavelengths ranging from 355 to 1064 nm assuming the aerosols to be smooth spheroids or Chebyshev particles. We show that the unique spectral dependence of the linear depolarization ratio (LDR) and extinction-to-backscatter ratio (or lidar ratio, LR) measured recently for stratospheric Canadian wildfire smoke can be reproduced by a range of model morphologies, a range of spectrally dependent particle refractive indices, and a range of particle sizes. For these particles, the imaginary part of the refractive index is always less than (or close to) 0.035, and the corresponding real part always falls in the range [1.35, 1.65]. The measured spectral LDRs and LRs could be produced by nearly-spherical oblate spheroids or Chebyshev particles whose shapes resemble those of oblate spheroids. Their volume-equivalent effective radii should be large enough (reff = 0.3 µm or greater) to produce the observed enhanced LDRs. Our study demonstrates the usefulness of triple-wavelength LDR measurements as providing additional size information for a more definitive characterization of the particle morphology and composition. Non-zero LDR values indicate the presence of nonspherical aerosols and are highly sensitive to particle shapes and sizes. On the other hand, the LR is a strong function of absorption and is very responsive to changes in the particle refractive index.

Study of the Variation of the Optical Properties of Nano-GaAs Coating with Particle Size

In this work, the optical properties of nano-GaAs coating are studied as a function of its particle size. Bulk Si is used as a basis for multi-layer optical reflection of nano-GaAs coating. This study is done by using a program performed in Matlab software, aiming to calculate the variation in reflectivity of the perpendicular and oblique incident light at wavelength of 1064[Formula: see text]nm with particle size, refractive index and energy gap of the coated multi-layer. This program is based on the Brus model and characteristic matrix theory. The results show that the reflectivity of Air/Si/Nano-GaAs/Si design, with particle size [Formula: see text] which equal is to 3.6[Formula: see text]nm is ([Formula: see text]%, [Formula: see text]%), approximately for oblique incidence at 45∘ and [Formula: see text]% for a perpendicular incidence. Given such a high reflectivity gained by this design, this study makes a major contribution to the field of fabricating Nd-YAG laser resonators.

Simultaneous retrieval of particle size and refractive index by extended interferometric particle imaging technique.

A method is presented for simultaneously inferring both the refractive index and the size of a particle with extended interferometric particle imaging technique. The optical system of extended IPI with opposite two-sheet illumination at dual scattering angles is laid out for the experiment. The size of a particle is evaluated by the interference fringe recorded at the scattering angle of 90°, which is from the two reflected lights with two counter-propagating sheet illuminations. And then the refractive index is calculated by the fringe pattern recorded in the side scattering angle region with one of two-sheet illumination when combined with droplet size determined. Experiments on the polystyrene microsphere and water droplet suggest that the method presented herein is promising for many relevant applications, such as fuel combustion and environmental monitoring, in accurately measuring both the particle size and its refractive index.

Vertical distribution of aerosol mass concentration over Pearl River Delta observed by Lidar during autumn and winter

This study aims to analyze the vertical distribution of aerosol particles during autumn and winter by deriving the number density of aerosol particles from Mie Lidar return signals. Haze has always existed in regions with low humidity and stable weather. In such regions,particle vertical distribution characters are needed for transport mechanisms. As a widely used instrument, Mie Lidar surfer from the uncertainties caused by the Lidar ratio and boundary value assumption. However, Mie Lidar is the most powerful tool to observe the atmospheric vertical distribution because it performs well in day and night under all weather conditions in comparison with passive sensors.Moreover, Mie Lidar is easier to carry compared with Raman Lidar.Lidar radiation principles were studied to understand the Lidar equation and its solution. Several parameters were carefully chosen for the numerical solutions. Instead of using boundary value for approximation, the Lidar parameter k was directly calculated on the basis of Lidar-validated parameters to avoid uncertainties. Thus, aerosol particles backscatter and extinction coefficient were retrieved by solving the Lidar equation and integrated for Aerosol Optical Depth(AOD) results. A Cimel CE318 sun photometer and an ASD Field Spec3 were used to measure AOD as validation data. Lastly, the number density of aerosol particles was derived on the basis of Mie theory with the estimation of aerosol particle distribution, size, and refractive index of particles.According to the number density vertical profile, nearly no difference was observed between the number density vertical profile of aerosol particles during daytime and nighttime in one day at a low altitude. This result indicated that the sunlight effect is ignorable for aerosol particle distribution near ground. The retrieved AODs with the CE318 and ASD observations showed a root mean square error of approximately 0.0541 and 0.0100, demonstrating that the retrieved result is reliable. The comparison with traditional method showed that the proposed algorithm in this study improved the accuracy of the traditional Lidar equation solution. The near-real distribution results showed aerosol particle distribution characteristics near the ground. The number density of aerosol particles in Guangzhou was mainly distributed in low-altitude regions, and its relationship with height was approximately a negative exponential distribution. The retrieved results of the aerosol particle number density were similar to those from the previous years, indicating that the air pollution in Guangzhou has not worsened. However, potential environmental threats and air pollution problems still need to be governed.Several uncertainties, such as changes in air temperature and pressure, validation of Lidar instrument k, and overlap factor, that could cause deviation were identified. The overlap factor and molecular backscatter coefficient were carefully calculated using the theoretical method. Frequent updates on Lidar parameters will be requested from the Lidar company in the future. The theoretical and experimental methods were combined for the calculation of the overlap factor and molecular backscatter coefficient. Raman Lidar was used to measure the actual Lidar ratios and characteristics of molecular scatter.The aerosol particle number density-retrieved algorithm was based on Lidar radiation principles and revealed the particles’ spatial distribution characters. The vertical distribution characters remained unchanged for several days under stable weather in the autumn and winter seasons, and its relationship with height was approximately a negative exponential distribution;hence, air conditions can have huge effect on human health. Air pollution problem still needs to be governed.