Dispersive Element Research Articles

Snapshot Imaging Spectrometer Based on Pixel-Level Filter Array (PFA).

Snapshot spectral imaging technology plays an important role in many fields. However, most existing snapshot imaging spectrometers have the shortcomings of a large volume or heavy computational burden. In this paper, we present a novel snapshot imaging spectrometer based on the pixel-level filter array (PFA), which can simultaneously obtain both spectral and spatial information. The system is composed of a fore-optics, a PFA, a relay lens, and a monochromatic sensor. The incoming light first forms an intermediate image on the PFA through the fore-optics. Then, the relay lens reimages the spectral images on the PFA onto the monochromatic sensor. Through the use of the PFA, we can capture a three-dimensional (spatial coordinates and wavelength) datacube in a single exposure. Compared with existing technologies, our system possesses the advantages of a simple implementation, low cost, compact structure, and high energy efficiency by removing stacked dispersive or interferometric elements. Moreover, the characteristic of the direct imaging mode ensures the low computational burden of the system, thus shortening the imaging time. The principle and design of the system are described in detail. An experimental prototype is built and field experiments are carried out to verify the feasibility of the proposed scheme.

Compact and adjustable compensator for AOD spatial and temporal dispersion using off-the-shelf components.

Random access multiphoton microscopy using two orthogonal acousto-optic deflectors (AODs) allows sampling only particular regions of interest within a plane, greatly speeding up the sampling rate. AODs introduce spatial and temporal dispersions, which distort the point spread function and decrease the peak intensity of the pulse. Both of these effects can be compensated for with a single dispersive element placed a distance before the AODs. An additional acousto-optic modulator, a custom cut prism, and a standard prism used with additional cylindrical optics have been demonstrated. All of these introduce additional cost or complexity and require an extended path length to achieve the needed negative group delay dispersion (GDD). By introducing a telescope between a transmission grating and the AODs, we correct for spatial and temporal dispersions in a compact design using only off-the-shelf components, and we show that the GDD can be tuned by translation of the telescope without adjustment of any other elements.

Effect of shift in refractive index of dispersive elements in waveband-shift-free optical-phase conjugator based on DFG

In this study, the effect of the shift in the refractive index between two dispersive elements on the output phase-conjugated (PC) wave power of waveband-shift-free optical-phase conjugators based on difference-frequency generation (DFG-OPCs) is analyzed. First, a numerical model of the DFG-OPC is built by considering the shift ∆n in the refractive index. The derived formula shows that the output PC wave power of DFG-OPCs depends on the shift in the refractive index. Subsequently, the dependence of the output PC wave power on the shift is confirmed analytically. Calculations indicate that the output PC wave power varies according to the shift. For a relatively fractional shift ∆n = 1.0e-6, the output PC power is degraded by 3 dB. Finally, acceptable values of the shift and temperature difference are calculated as functions of the length of the dispersive element. It is illustrated in this study that the acceptable value of shift in the refractive index increases as the length of the dispersive element is reduced and that the output PC wave power can be stabilized against changes in temperature.

Multipass etalon cascade for high-resolution parallel spectroscopy.

Spectral contrast, the ability to measure frequency components of vastly different intensity, is critical in optical spectroscopy. For high spectral contrast at high spectral resolution, scanning etalons are generally used, as they allow cascading multiple dispersive elements. However, scanning instruments are inherently limited in terms of acquisition speed. Here we report a single-shot cascaded spectrometer design, in which light is dispersed along a single dispersion direction at every stage and thus can be recirculated in the same etalon multiple times. Using this design principle, we demonstrate single-shot spectral measurements at sub-gigahertz resolution and unprecedented spectral contrast (∼80dB).

Tunable near infrared laser

The article introduces a tunable NIR laser. The tuning process realizes by the dispersion elements placed inside the resonator. Energy parameters depending on the laser operating mode are presented. The possibility of smooth tuning of the fundamental lasing wavelength depending on the rotation parameters of the dispersion element is shown.

Evaluation of hemato-biochemical indices and oxidative stress in goats: a potential risk towards arsenic toxicity in contaminated zone of West Bengal, India

Arsenic is one of the widely dispersed elements in the Earth’s crust and exists in the environment due to natural and anthropogenic sources. The toxin is greatly expanded through intensive application of groundwater in agriculture in the region within the Green Revolution framework. It is an environmental chemical element of high concern for human and animal health. Agricultural land is constantly contaminated with arsenic due to application of groundwater for irrigation purposes. Animals, being exposed to arsenic through contaminated drinking water, exhibit major abnormalities in the blood and tissues of animals prior to the excretion in the urine and feces. This present study was conducted to evaluate the hemato-biochemical indices and blood oxidative stress in thirty Black Bengal goats irrespective of age, sex, breeding system of Ghetugachi village of Nadia district of West Bengal, India, and control Akna village of Polba block of Hoogli district of West Bengal, India. There was a significant reduction in hemoglobin, red blood cells and white blood cells, packed cell volume, and total serum protein with a significant elevation of aspartate aminotransaminase, alanine aminotransaminase, blood urea nitrogen, and creatinine. Elevated corpuscular osmotic fragility depicted an altered mechanism associated with the deviation of the normal functioning of erythrocytes. Goats harboring in the grazing arsenic endemic zone also showed a significantly higher arsenic burden in blood. The affected goats further exhibited declined superoxide dismutase and catalase activities of erythrocytes and plasma nitrite levels with increased lipid peroxidation and protein carbonyl level. Our investigation concluded that goats of the arsenic-affected areas are suffering from a subclinical form of arsenic toxicity, which is proved through the altered hemato-biochemical and oxidative stress indices with a higher arsenic concentration in the blood.

Chromo-modal dispersion for optical communication and time-stretch spectroscopy.

Dispersion management is critical in many optical applications, whether to reduce impairments in fiber optic communication or chirp pulse amplification, or to create time stretch instruments for single-shot continuous recording of fast phenomena. The most common solutions for achieving large dispersion with low loss include dispersion compensation fiber, fiber Bragg grating, and diffraction grating pairs. Such dispersive elements have finite operational bandwidth, limited total dispersion, or insufficient power handling. In this Letter, we demonstrate a new, to the best of our knowledge, implementation of the chromo-modal dispersion device based on a silicon waveguide slab that addresses these limitations. The device provides extremely large dispersion with a widely tunable spectrum. We also propose a new time-stretch spectrometer where the absorption cell simultaneously provides spectrum-to-time mapping for fast single-shot spectroscopy.

Production of Multi-Gigawatt Sub-Nanosecond Microwave Pulses by the Method of Chirped-Pulse-Amplification

We demonstrate theoretically the possibility of efficient amplification and subsequent recompression of sub-nanosecond (0.25-0.3 ns) microwave superradiant pulses, which underwent preliminary stretching and became frequency-chirped. Similar technique, known as Chirped Pulse Amplification (CPA), is now successfully used in petawatt-class lasers. According to simulations, a microwave CPA scheme comprising a relativistic Cherenkov traveling-wave tube (TWT) as an active unit and dispersive elements (stretcher and compressor) based on multi-fold helically corrugated oversized waveguides can produce Ka-band sub-nanosecond pulses with peak power of about ten gigawatts.

Gradient Waveguide Thickness Guided-Mode Resonance Biosensor.

Portable systems for detecting biomolecules have attracted considerable attention, owing to the demand for point-of-care testing applications. This has led to the development of lab-on-a-chip (LOC) devices. However, most LOCs are developed with a focus on automation and preprocessing of samples; fluorescence measurement, which requires additional off-chip detection instruments, remains the main detection method in conventional assays. By incorporating optical biosensors into LOCs, the biosensing system can be simplified and miniaturized. However, many optical sensors require an additional coupling device, such as a grating or prism, which complicates the optical path design of the system. In this study, we propose a new type of biosensor based on gradient waveguide thickness guided-mode resonance (GWT-GMR), which allows for the conversion of spectral information into spatial information such that the output signal can be recorded on a charge-coupled device for further analysis without any additional dispersive elements. A two-channel microfluidic chip with embedded GWT-GMRs was developed to detect two model assays in a buffer solution: albumin and creatinine. The results indicated that the limit of detection for albumin was 2.92 μg/mL for the concentration range of 0.8–500 μg/mL investigated in this study, and that for creatinine it was 12.05 μg/mL for the concentration range of 1–10,000 μg/mL. These results indicated that the proposed GWT-GMR sensor is suitable for use in clinical applications. Owing to its simple readout and optical path design, the GWT-GMR is considered ideal for integration with smartphones or as miniaturized displays in handheld devices, which could prove beneficial for future point-of-care applications.

Hydrogel gratings with patterned analyte responsive dyes for spectroscopic sensing.

This is an unprecedented report of hydrogel gratings with an analyte responsive dye immobilised in alternating strips where the patterned dye is its own dispersive element to perform spectroscopy. At each wavelength, the diffraction efficiency of hydrogel gratings is a function of dye absorbance, which in turn is dependent on the concentration of analytes in samples. Thus, changes in intensity of diffracted light of hydrogel gratings were measured for sensing of analytes. Equally, the ratio of diffracted intensities at two wavelengths was used for quantification of analytes to reduce errors caused by variations in intensity of light sources and photobleaching of dyes. 15.27 μm pitch gratings were fabricated by exposing 175 μm thick films of photofunctionalisable poly(acrylamide) hydrogel in a laser interferometric lithography setup, generating an array of alternating lines with and without free functional groups. The freed functional groups were reacted with pH sensitive fluorescein isothiocyanate to create gratings for measurement of pH. The ratio of intensity of diffracted light of hydrogel gratings at 430 and 475 nm was shown to be linear over 4 pH units, which compares favourably with ∼2 pH units for conventional absorption spectroscopy. This increased dynamic range was a result of cancellation of the opposite non-linearities in the pH response of the analyte responsive dye and the diffraction efficiency as a function of dye absorbance.

The (Self)portrait of a Writer: A Hermeneutic Reading of Virginia Woolf’s (Auto)biographical Writings

Woolf’s maturing as a writer was deeply influenced by her traumatic experiences in childhood, the (in)capacitating states of mental instability, as well as her proto-feminist convictions. Long before Barthes, she toppled the traditional position of the author, and her literary enshrinement of “the other reality” reached unity with the world rather than individuality. This article ponders Woolf’s creative impulse and investigates her autobiographical writings to show the import of their impact on her fiction, which, as Woolfian scholarship suggests, can be viewed as autobiographical, too. I argue that philosophical hermeneutics sheds light on the self-portrait that emerges from Woolf’s autobiographical writings and offers a rewarding insight into her path of becoming an author. I assert that Paul Ricoeur’s philosophy of subjectivity, and, in particular, his notion of narrative identity provide a route to examine how Woolf discovers her writing voice. In light of his hermeneutics of the self, the dispersed elements of the narrative of life can be seen as a possibility of self-encounter. Woolf’s writings bespeak her gradually evolving self-knowledge and self-understanding, which come from the configuration of those separate “stories” into a meaningful whole. The article also interprets Woolf’s autobiographical writings through the prism of Michel Foucault’s reflection on discourse and subjectivity, indicating that her texts instantiate his assertion of the subject’s constant disappearance.

Aumento de la presión del cárter por abrasión de los cilindros y la incidencia en la potencia del motor Wärtsilä Vasa 32

INTRODUCCIÓN. En los motores Wärtsilä Vasa 32 pertenecientes a una empresa de servicios petroleros, se ha evidenciado un aumento de la presión del cárter del motor debido al descenso de la compresión desde la cámara de combustión, producido por un desgaste abrasivo en las camisas de los cilindros, lo que ha provocado una disminución anual de la potencia. OBJETIVO. Determinar el desgaste producido en una camisa, los valores de los elementos abrasivos que se encuentran dispersos en el combustible y aceite, y la dependencia de la potencia en función de la presión del cárter. MÉTODO. Realización de mediciones con instrumentos de metrología y análisis de elementos dispersos en el combustible y aceite en laboratorios internacionales. RESULTADOS. Los análisis de aceite y combustible indicaron una excesiva cantidad de vanadio, aumentando el desgaste abrasivo en las camisas. Este desgaste se comprobó midiendo el diámetro y la rugosidad media de una camisa, después de 12000 horas de funcionamiento y cuyos valores no estaban dentro de los límites recomendados por el fabricante del motor. DISCUSIÓN Y CONCLUSIONES. Existe una correlación lineal decreciente entre la potencia del motor y la presión del cárter. Además, se determinó que el crudo ecuatoriano tiene una elevada cantidad de vanadio.

Archaeological ash deposits and soils formed on ash in the south of the East European Plain

Ash as an anthropogenic substrate is widely found at archaeological sites in the south of the East European Plain. Investigations of archaeological ashes, the results of which are presented here, have been conducted in three regions that differ in climate and extent of forest cover (from 29 to 1.5%): 1) typical forest–steppe; 2) piedmont forest-steppe with islands of groves; 3) steppe, almost woodless landscapes. Using spectrometry and X-ray analysis, the present study investigates the chemical composition of ancient ash and ash experimentally produced from different sorts of fuel, as well as the geochemistry of soils developed on ash deposits. For ashing, 25 samples of plants that potentially might have been used as fuel were selected, as well as dung from cattle and horses. Using the geometric mean values of concentrations of diagnostic elements, a formula was proposed for evaluating the pedogenetic transformation of ash, which is based on the ratio of accumulation elements (Cu, As, SiO2, Al2O3 and Pb) and dispersion elements (Sr, Ca, Со, Mg and Na2O). The procedure makes it possible to date the pedogenetically transformed ash through the stable associations of chemical elements diagnostic of the geochemical accumulation and dispersion in the soils formed on ash. Geochemical criteria were established for identifying ash that results from the combustion of dung, wood or a combination of different fuels. This study opens prospects for further research into archaeological ash deposits in varying cultural, temporal and environmental conditions.

The effect of Ce3+ doping on structural, optical, ferromagnetic resonance, and magnetic properties of ZnFe2O4 nanoparticles

Herein, we used the ultrasound irradiation to assist the sol–gel method for the synthesis of spinel ZnCexFe2 − xO4 nanoparticles. The patterns obtained from energy dispersive x-rays (EDX) analysis and elements mapping demonstrate the appropriate elemental stoichiometry and spatial distribution in the prepared samples. The Rietveld refinement patterns revealed the successful synthesis of the cubic-structured ZnFe2 − xCexO4 without any secondary phases. The crystallite size of ZnFe2 − xCexO4 ranged from 7 to 11 nm. Also, the optical bandgap for ZnFe2 − xCexO4 decreased from 2.1 eV to 1.77 eV. Electron paramagnetic resonance (EPR) spectroscopy was used to study the ferromagnetic resonance (FMR) characteristics of the ZnFe2 − xCexO4 samples. The resonance field was increased from 3362.65 Gauss to 3401.76 Gauss, while the line width decreased from 598.90 to 455.72 Gauss. The saturation magnetization was enhanced from 2.43 emu/g for x = 0.00 to 9.38 emu/g for x = 0.02. In addition, the values of coercivity (Hc) and remanence magnetization (Mr) were significantly lowered. The great value of saturation magnetization together with low values of Hc and Mr of Ce3+-substituted Zn ferrites makes them potential candidates for the microwave absorption field.

Circuit Modularization of Quantum Optical Systems

Quantum optics and nanophotonics are the basis of future communications and computation technologies. Thus, there is an ever-increasing need for analysis and design tools that are suitable for large, complex, and multielement systems. However, full quantum analysis of systems requires writing the full quantum Hamiltonian, which is usually possible only in simple cases that are easy to analyze analytically, and especially difficult when the system contains dispersive and dissipative elements. Here we use circuit theory to modularize the modeling of the quantum Hamiltonian, and therefore the entire quantum system. We use the notion of optical metatronics---circuit analog for nanophotonic structures---to model our photonic system as an electronic circuit, and show how each coupling term in the Hamiltonian can be written using classical equivalent circuits. Thus, the quantum-interaction term between any two elements can be analyzed, designed, and optimized using the vast library of circuit engineering tools, which by their very nature enable the design of complex, multielement realistic systems. Our work generalizes the current theoretical treatment of quantized nanophotonic systems, paving the way for a systemic, modularized modeling of large-scale systems.

Design of a Multimode Interferometer-Based Mid-Infrared Multispecies Gas Sensor

A $1\times 2$ multimode interferometer beam splitter based on mid-infrared emitting chalcogenides waveguides is designed. This device multiplexes mid-infrared light in two channels whose respective passbands overlap either CO2 or CO absorption bands, respectively between 4.20- $4.32~\mu \text{m}$ and 4.50- $4.86~\mu \text{m}$ . The proposed device offers a low-cost solution for monolithic combination of broadband on-chip mid-infrared light emission with dispersive spectroscopic element devoted to mid-IR multigas sensing applications. Based on restrictive interference mechanism in a $1\times 2$ multimode interferometer, the multimode section dimensions (width and length) are engineered to increase the imbalance between the two ports for the two passbands and consequently to increase the output contrast ratio. Tolerances to variations from the optimum device design resulting from processing conditions (materials fabrication and sputtering, photolithography and dry etching steps) are assessed. In particular, the $1\times 2$ multimode interferometer diplexer spectral transmission is investigated as a function of deposited film refractive index and multimode section dimensions (width and length) deviation from designed values. Input and output ports tapering is introduced to reduce the device insertion loss.

Properties and potential applications of reflection focusing and dispersion plane gratings

Plane gratings are widely used as dispersion elements in spectral analysis from the infrared to x-ray regions. This study proposes an optical element, consisting of only a reflection focusing and dispersion plane grating (RFPG) designed for a specific wavelength. A raytracing simulation and a visible light experiment were performed to verify the focusing and wavelength dispersion properties of the proposed RFPG. The raytracing simulation result shows that the designed 635 nm RFPG has a spectral resolution (λ/∆λ) of 423 (linear dispersion = 493.8 eV/m) under specific conditions. Additionally, in the visible light experiment, the spectral resolution of 423 (linear dispersion = 493.8 eV/m) and band range of ±25 nm were obtained at the target wavelength of 635 nm. The experimental results indicate that the proposed optical element, RFPG, exhibits focusing and dispersion properties for a designed wavelength. It is a potential tool for the study of x-ray fluorescence, absorption, and advanced x-ray sources, such as laser wakefield Betatron x-ray sources.

A Solid-State Near-IR Laser for Spin-Exchange Optical Pumping

A mean of spin-exchange optical pumping is considered for the polarization of noble gases using a tunable laser. The possibility is considered of creating a solid-state source of laser radiation with dispersive elements in its cavity in order to achieve spin-exchange optical pumping.

Carrier-less phase retrieval receiver leveraging digital upsampling.

Phase retrieval (PR) receivers can reconstruct the full electrical field of the signal using only intensity measurements without any optical carrier. In this Letter, we investigate the requirement of digital upsampling and receiver bandwidth of the PR receiver based on alternative projection employing a dispersive element. An iteration scheme averaging the interleaved upsampled symbols to maintain two samples per symbol for the estimated complex-valued signal is proposed and experimentally demonstrated with fast algorithm convergence. The PR uses a modified Gerchberg-Saxton algorithm. Experimentally, we measure Nyquist-shaped 30-GBaud quadrature phase shift keying signals after 55-km single-mode fiber transmission using only 110 and 250 iterations to reach, respectively, the 20% and 7% forward-error correction threshold levels.

Reactive LES-Euler/Lagrange modelling of bubble columns considering effects of bubble dynamics

Bubble columns are complex multiphase reactors producing large contact areas for mass transfer and subsequent chemical reactions. For allowing a deeper insight into this complexity and providing strategies for process optimisation, CFD (computational fluid dynamics) has become a standard tool. However, accurate models are needed to reproduce correctly such dynamic systems. Numerical computations of reactive bubble columns are conducted based on a LES-Euler/Lagrange approach. For extending this approach beyond the point-mass assumption for the dispersed elements, a bubble oscillation model based on stochastic generation of eccentricity and motion angle is proposed. The effects of bubble dynamics are modelled in the interfacial forces accounting for instantaneous eccentricity. A dynamic Sherwood number is used to consider bubble dynamics in the mass transfer. The influence of chemical reactions in species consumption within the liquid phase was modelled through the enhancement factor. Large Eddy Simulation (LES) was used for calculating the fluid flow with momentum source terms for bubbles and modelling sub-grid-scale (SGS) turbulence in the continuous phase through a transport equation for the turbulent kinetic energy. The effect of sub-grid-scale (SGS) turbulence on bubble motion, and also SGS turbulence modification by bubbles (BIT) is considered, introducing an extra source term in a kSGS equation. This source term automatically accounts for turbulence dissipation as well as enhancement (i.e. BIT). Numerical simulations of the chemisorption process for CO2 bubbles rising in highly concentrated NaOH solutions were compared with data presented in the literature. A very good agreement was only found when applying the full bubble dynamics model.