Minimum Absorption Coefficient Research Articles

Study of the preparation and properties of hydrophobic and high strength geopolymers

An excellent hydrophobic geopolymer (GP) composite modified by fatty acid and polydimethylsiloxane (PDMS) with high mechanical strength was prepared successfully. The results of this research show that, when the mass fraction of fatty acid and PDMS were 50 % and 5 % respectively, the maximum water contact angle, 24 h minimum water absorption and maximum softening coefficient of GP obtained by composite modification method could reach 143°, 0.36 % and 0.88, respectively. Meanwhile, the maximum compressive strength exceeds 47.25 MPa.

Water vapor concentration measurements in high purity gases by means of comb assisted cavity ring down spectroscopy

In manufacturing processes of semiconductor industry accurate detection and monitoring of water vapor concentration in trace amount is of great importance. The ability to perform reliable measurements in ultra-pure gases, with a wide dynamic range and low uncertainty, can have a substantial impact on product quality and process performances. Here, we report on the development of a second-generation comb-assisted cavity ring-down spectrometer and present H2O mole fraction measurements in high-purity N2 gas. Based on the use of a pair of phase-locked lasers and referenced to an optical frequency comb synthesizer, the spectrometer allowed to record high-quality absorption spectra in coincidence with the 32,2→22,1 H2O transition at 1.3946μm. Retrieval of water mole fractions, at levels as low as 380 part per billion, was accomplished through a careful spectra analysis procedure based on the use of refined line shape models which include speed-dependent effects. Measurements were performed with a statistical reproducibility of 5 parts per billion, for an integration time of about 0.2 s. The noise equivalent and minimum detectable absorption coefficients were found to be 3.1 × 10−11 cm−1/Hz and 6.5 × 10−12 cm−1, respectively. This latter allowed for a minimum detectable water mole fraction (limit of detection) of 160 parts per trillion. Finally, the main sources of systematic uncertainty have been discussed and quantified.

Highly sensitive portable laser absorption spectroscopy formaldehyde sensor using compact spherical mirror multi-pass cell

A portable sensor with an optical case dimension of 46 × 28 × 16 cm3 based on laser absorption spectroscopy for highly sensitive measurement of formaldehyde was reported. A compact improved spherical mirror multi-pass cell consisting of two 5-cm diameter spherical mirrors separated by 17.7 cm was developed. The cell offered a sample volume of 350 mL and an optical absorption path length of 50.6 m, giving a high path length-to-volume ratio of 14.6 cm−2. The sampling response time was less than 1 s, allowing the application of rapid spectral background subtraction technique to effectively suppress optical fringes. The achieved detection limit was 650 pptv (1σ, 1 s), corresponding to a minimum detection absorption coefficient of 2.3 × 10−9 cm−1. The capability of the HCHO sensor was demonstrated by two days of continuous indoor air monitoring. The developed portable sensor is suitable for mobile and fast indoor air quality measurements.

Development of high efficiency Ce1–BMgBO2 buffer and perovskite HTL based CIGSSe thin film solar cell using a simulation approach

Performance of the conventional (ZnMgO:Al/ZnMgO/CIGSSe) photovoltaic device has been enhanced by using novel magnesium-doped cerium oxide (Ce1–BMgBO2) as a buffer and perovskite as a hole transport layer (HTL) material. At the beginning of this paper, three experimental photovoltaic devices having an efficiency of 19.8%, 19.8% and 20% have been simulated and verified using the AFORS-HET simulation tool. Later, a low resistivity (ρ), wide energy bandgap (Eg), and minimum absorption coefficient (α) Ce1–BMgBO2 material is applied to the conventional device instead of the ZnMgO buffer layer. As a result, the efficiency of the proposed-1 photovoltaic device has been enhanced (20–26.59%). Due to a deficiency of HTL material, the proposed-1 device cannot properly suppress the photogenerated minority carrier recombination losses. Further, perovskite as a HTL material is applied between the CIGSSe/Mo back layers in the proposed-1 device. Therefore, the proposed-2 device instantly reduces the recombination losses and enhances the efficiency (28.93%) and EQE.

Broadband optical limiting in nanohybrids of graphene grafted peripheral (non-peripheral) pyrene substituted phthalocyanines with a low linear absorption

In nonlinear optics, nanohybrids from the functionalization of graphene and organic molecules can be an interesting area of research. In this work, nanohybrid materials consisting of pyrene conjugated peripheral phthalocyanines and non-peripheral phthalocyanines, which are non-covalently attached to the graphene exhibit broadband optical characteristics and broadband limiting optical behavior through a two-photon absorption process with a high degree of transparency. For confirming non-covalent functionalization, optical as well as spectroscopic studies like UV–vis absorption, fluorescence studies, transient absorption, FTIR, XPS, Raman, AFM techniques, etc., were employed. Distinct morphologies are observed for these nanohybrids, such as -nanohybrids with a cylindrical shape in the non-peripheral case whereas a conical shaped nanohybrids in the peripheral case. Furthermore, Raman studies reveal a shift of 8 cm−1 for the 2D peak of both nanohybrids in comparison with that of graphene confirms the strong π-π interaction, which is the maximum shift in a non-covalent interaction between pyrene attached graphene. In a major finding, a donor-acceptor combination is established in these nanohybrids, which makes them important nonlinear optical materials. The nonlinear absorption coefficients of 112 ± 7 cm/GW and 228 ± 12 cm/GW were obtained for these nanohybrids. Compared to the existing reported values, these nanohybrids with the minimum linear absorption coefficient (1.15 cm−1 and 1.25 cm−1), display broadband nonlinear optical characteristics with low optical limiting thresholds (0.9 and 0.83 Jcm−2), which is achieved through the transfer of electrons from Pc core to pyrene anchored graphene, enable them standout candidates for photonic applications.

Influence of SnMnO2 window layer on enhancing the performance of CIGSSe thin-film solar cell

In this paper, the thickness and doping concentrations of the double buffer cell-based conventional CIGSSe solar cells are optimized, and alignment of the energy band of the optimized solar cell (ZnMgO/CIGSSe) is carried out, thus obtaining an increase in efficiency from 23.35 % to 27.88 %. Further, a new design is proposed of low cost, low resistivity, minimum absorption coefficient, tunable energy bandgap (3.6–4.44 eV) with tin-doped manganese oxide Sn1−xMnxO2 material (x = 0.5) as a window layer in conventional solar cell design. The thin-film solar cell efficiency has improved from 23.35 % to 29.05 % by aligning the energy bandgap with an optimized thickness and doping concentration. The proposed Sn1−xMnxO2 window layer-based thin-film solar cell is more convenient in instantly absorbing the maximum blue light with reduced recombination loss, increased efficiency and external quantum efficiency. The simulated parameters of the conventional model are compared and validated with the existing conventional solar cells.

Ni0.48Cu0.12Zn0.4Fe2O4+ paraformaldehyde nanocomposites as microwave absorbent dominant materials

A series of nanocomposite materials were developed to study microwave absorption properties in 8.2–12.4 GHz (X-band) and 12.4–18 GHz (Ku-band) regions. Nanocomposites of ferrite and polymer constituents with ordered combination (x) wt% Ni0.48Cu0.12Zn0.4Fe2O4 + (1-x) wt% paraformaldehyde, (x = 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0) were prepared by mechanical alloying method. Microwave digestion system was used to prepare nanopowders of Ni0.48Cu0.12Zn0.4Fe2O4 by microwave hydrothermal method. Microwave absorption studies revealed that synergistic combination of ferrite and paraformaldehyde phases in the synthesized composites enhanced the ability to absorb electromagnetic waves screening maximum of 99.7% power of incident electromagnetic waves in X and Ku band frequency regions. The results proved that maximum reflection coefficient of 0.925 and minimum absorption coefficient of 0.072 at 12 GHz were achieved and maximum shielding effectiveness of 26.7 dB was obtained with significant contribution from absorption. The studies proved that maximum synergistic effects were achieved for 50% polymer phase of the sample wherein balanced combination of dielectric and magnetic losses gives rise to minimum reflection loss. The results confirmed that the prepared absorbent dominant materials are found to be potential candidates for designing microwave filters in radar, stealth and satellite applications.

Impact of ZnMnO buffer and SnMnO2 window layer on enhancing the performance of CIGSSe thin-film solar cell

A conventional copper indium gallium sulphur diselenide (CIGSSe) thin-film with double buffer layer solar cell structure of Al/MgF2/ZnO: B/ZnO/ZnMgO/CIGSSe/Mo(S, Se)/Mo is simulated. A high conductivity, low cost and minimum absorption coefficient, manganese doped zinc oxide (Zn1-xMnxO) semiconductor material as a buffer-1 layer is used instead of ZnO in the conventional solar cell. It is observed that the new proposed structure increases the efficiency by 28.80%. Smaller energy band-gap and higher absorption coefficient of ZnO: B window layer material does not absorb the short wavelength photons, thus a decrease in the external quantum efficiency (EQE) of conventional cells is observed. To overcome this, a new structure is proposed to have a wide energy band-gap. A tin-doped manganese oxide (Sn1-xMnxO2) is used as window layer material instead of ZnO: B. A new thin-film solar cell (TFSC) design is proposed where SnMnO2 as window and ZnMnO as buffer-1 is proposed, which helps in instantly absorbing the maximum blue light, reducing recombination losses, increasing efficiency and EQE. This new TFSC design provides a better efficiency of 29.40%.

A Prototype Evanescent Wave-Coupled Cavity Ring-down Spectrometer for Probing Real-Time Aggregation Kinetics of Gold and Silver Nanoparticles.

We report on the development of a simple, linear optical cavity-based system combining evanescent wave (EW) with high-sensitive cavity ring-down spectroscopy (CRDS) technique using a diode laser at 644 nm and a right-angled prism for evanescent field generation on prism surface. We characterized the setup in detail and achieved an optimum ring-down time of 159.4 ns and a minimum absorption coefficient of αmin = 1.67 × 10-6 cm-1. We utilized this setup to investigate the salt-induced aggregation kinetics of gold (Au) and silver (Ag) nanoparticles (NPs) at the prism interface with high-sensitivity. We evaluated the extinction rates on the surface due to Au and Ag NPs aggregation and examined the variations due to their respective concentrations. To demonstrate the applicability of the developed EW-CRDS prototype setup to different molecular systems, we investigated the urease-bound aggregation kinetics of the Au and Ag NPs which has not been explored earlier by this linear cavity geometry. We finally illustrated the aggregation dynamics through surface imaging, thus demonstrating an alternative analytical approach to monitor interfacial phenomena using EW-CRDS technique.

Mapping the Impact of Land Use and Land Cover Change on Urban Land and Vegetation in Osun State, Nigeria

Urban expansion along with other changes in land use and land cover is a global phenomenon and most parts of Western Nigeria have experienced tremendous changes in recent past. Osun state, located in Western Nigeria, was originally made up of mostly traditional farming communities. These communities have witnessed rapid urbanisation in the last few decades and most of the communities previously known to be farming communities have transformed to modern well-known cities. This project examines the use of Remote Sensing in mapping of Land Use Land Cover in Osun state over a period of 30 years (1986 to 2016) using Landsat (MSS, TM, and ETM+) images. The aim of this study is to produce a land use/land cover map of Osun state at three epochs in order to detect the changes that have taken place particularly in the built up and Vegetation areas. Landsat Images of Osun state in 1986, 2006 and 2016 were processed into five land use classes namely: Water body, Vegetation, Wetland, Built-up and Bare land. Total area of land use in each class were determined along with percentage change area, Land Consumption Rate and Land Absorption Coefficients. The result of the work shows that built-up area changed from 20.52% in 1986 to 30.71% in 2006 and then 34.45% in 2016. Land Consumption rate was 0.068 in 2016 which is indication of highly compacted living environment. The minimum Land Absorption Coefficient observed was 0.027 in between 2006 and 2016, which indicates that land is acquired for built-up development at very high rate. The resultant effect of these observed changes was a reduction of the vegetation class from 35.82% in 1986 to 31.14% in 2006 and then 23.83% in 2016. The results in this study may influence new land policy that will enhance sustainable use of land in Osun state.

Simultaneous detection of C<sub>2</sub>H<sub>6</sub>, CH<sub>4</sub>, and <i>δ</i><sup>13</sup>C-CH<sub>4</sub> using optical feedback cavity-enhanced absorption spectroscopy in the mid-infrared region: towards application for dissolved gas measurements

Abstract. Simultaneous measurement of C2H6 and CH4 concentrations, and of the δ13C-CH4 isotope ratio is demonstrated using a cavity-enhanced absorption spectroscopy technique in the mid-IR region. The spectrometer is compact and has been designed for field operation. It relies on optical-feedback-assisted injection of 3.3 µm radiation from an interband cascade laser (ICL) into a V-shaped high-finesse optical cavity. A minimum absorption coefficient of 2.8×10-9 cm−1 is obtained in a single scan (0.1 s) over 0.7 cm−1. Precisions of 3 ppbv, 11 ppbv, and 0.08 ‰ for C2H6, CH4, and δ13C-CH4, respectively, are achieved after 400 s of integration time. Laboratory calibrations and tests of performance are reported here. They show the potential for the spectrometer to be embedded in a sensor probe for in situ measurements in ocean waters, which could have important applications for the understanding of the source and fate of hydrocarbons from the seabed and in the water column.

Absolute density measurement of nitrogen dioxide with cavity-enhanced laser-induced fluorescence**Project supported by the National Natural Science Foundation of China (Grant Nos. 11504112, 91536218, and 11604100).

The absolute number density of nitrogen dioxide (NO2) seeded in argon is measured with cavity-enhanced laser-induced fluorescence (CELIF) through using a pulsed laser beam for the first time. The cavity ring down (CRD) signal is acquired simultaneously and used for normalizing the LIF signal and determining the relationship between the measured CELIF signal and the NO2 number density. The minimum detectable NO2 density down to (3.6 ± 0.1) × 108 cm−3 is measured in 60 s of acquisition time by the CELIF method. The minimum absorption coefficient is measured to be (2.0 ± 0.1) × 10−10 cm−1, corresponding to a noise equivalent absorption sensitivity of (2.2 ± 0.1) × 10−9 cm−1·Hz−1/2. The experimental system demonstrated here can be further improved in its sensitivity and used for environmental monitoring of outdoor NO2 pollution.

Fabrication of high refractive index TiO2 films using electron beam evaporator for all dielectric metasurfaces

Flat optics suffer meager efficiency due to plasmonic losses at visible wavelengths. This issue has been addressed in this study by the substitution of dielectric materials. For this purpose, optical parameters (real and imaginary parts of refractive index) and surface roughness of TiO2 films were optimized, which are pre-requisite for the development of highly efficient dielectric metasurface devices. Electron beam evaporator was employed to deposit various ultrathin TiO2 films with subwavelength thickness. These deposited films were further processed via annealing at various temperatures to achieve the appropriate optical parameters. SEM analysis confirmed the absence of craters, cracks and rugged type features, whereas, AFM analysis revealed the smoothness of deposited films with least roughness. High refractive index above 2.2 with minimum absorption coefficient in the visible region was studied through ellipsometry analysis. FTIR spectroscopy showed transmission over 90% from the deposited thin film on glass substrate. The results of this study would have significant implications for material processing at nanoscale and dielectric metasurface fabrication which would in turn eliminate the requirement of costly and sophisticated setups for such fabrications.

High Refractive Index Ti3O5 Films for Dielectric Metasurfaces**M. Q. M. acknowledges Information Technology University of the Punjab, Lahore, Pakistan for financial support. J. R. acknowledges the financial support by Engineering Research Center Program (NRF-2015R1A5A1037668), I. K. acknowledges global Ph.D. fellowship (NRF-2016H1A2A1906519), and N. R.-H. acknowledges the KRF fellowship (NRF-2017H1D3A1A02011379) through the National Research Foundation of Korea (NRF) funded by the

Ti3O5 films are deposited with the help of an electron beam evaporator for their applications in metasurfaces. The film of subwavelength (632 nm) thickness is deposited on a silicon substrate and annealed at 400°C. The ellipsometry result shows a high refractive index above 2.5 with the minimum absorption coefficient in the visible region, which is necessary for high efficiency of transparent metasurfaces. Atomic force microscopy analysis is employed to measure the roughness of the as-deposited films. It is seen from micrographs that the deposited films are very smooth with the minimum roughness to prevent scattering and absorption losses for metasurface devices. The absence of grains and cracks can be seen by scanning electron microscope analysis, which is favorable for electron beam lithography. Fourier transform infrared spectroscopy reveals the transmission and reflection obtained from the film deposited on glass substrates. The as-deposited film shows high transmission above 60%, which is in good agreement with metasurfaces.

Computer simulations of X-ray six-beam diffraction in a perfect silicon crystal. II.

This paper reports computer simulations of X-ray six-beam (000, 220, 242, 044, -224, -202) diffraction in a perfect silicon crystal of large thickness where the super-transmission effect prevails, i.e. about 2 cm or more for an X-ray photon energy of 8 keV. Both the plane-wave angular dependence and the six-beam section topographs, which are obtained in experiments with a two-dimensional slit, are calculated. The angular dependence is computed by means of an eigenvalue problem in accordance with Ewald's theory. The section topographs are calculated by means of a fast Fourier transformation procedure from the angular to real space. It is shown that under the effect of X-ray super-transmission the quadrupole part of the photoelectric absorption as well as the Compton scattering give apparent contributions to the minimum absorption coefficient. Comparison of experimental and theoretical results by means of measuring the effective absorption coefficient is proposed. The section topographs for a thick crystal are asymmetric and polarization sensitive. These properties are explained through the angular dependence and the stationary phase method.

Control of gold nano-domes to design an all-optical switch by simultaneously binary and continuous operated optimization

This paper presents an efficient evolutionary method to optimize an array of plasmonic nano-domes in order to design an optical switch. In the proposed switch, the optical switch has been excited by two monochromatic incident plan-waves with the same frequency and two polar angles "$$\uptheta =0$$?=0" and "$$\uptheta =\uppi /2$$?=?/2". When only the signal with $$\uptheta =0$$?=0 is applied, the incident wave is transmitted and when both signals are applied to the switch simultaneously, coherent perfect absorption (CPA) occurs and the two incident waves are suppressed. Therefore, the signal with $$\uptheta =\uppi /2$$?=?/2 acts as control signal. Since the CPA efficiency depends strongly on the number of plasmonic nano-domes, on their location and geometric characterization, a new efficient optimization method named "fuzzy adaptive modified particle swarm optimization" (FAMPSO) is proposed to design an optimized array of the plasmonic nano-domes in order to achieve the maximum absorption coefficient in the off-state and the minimum absorption coefficient in the on-state. In the FAMPSO algorithm a group of birds controlling the presence (`1') or the absence (`0') and geometric characterization of nano domes in the array.

Investigating the optical XNOR gate using plasmonic nano-rods

In this paper, a coherent perfect absorption (CPA)-type XNOR gate based on plasmonic nano particle is proposed. It consists of two plasmonic nano rod arrays on top of two parallel arms with quartz substrate. The operation principle is based on the absorbable formation of a conductive path in the dielectric layer of a plasmonic nano-particles waveguide. Since the CPA efficiency depends strongly on the number of plasmonic nano-rod and the nano rod location, an efficient binary optimization method based the Particle Swarm Optimization (PSO) algorithm is used to design an optimized array of the plasmonic nano-rod in order to achieve the maximum absorption coefficient in the ‘off’ state and the minimum absorption coefficient in the ‘on’ state. In Binary PSO (BPSO), a group of birds consists a matrix with binary entries, control the presence (‘1′) or the absence (‘0′) of nano rod in the array.

Investigating the optical NOR gate using plasmonic nanorods

SummaryIn this paper, a coherent perfect absorption‐type NOR gate based on plasmonic nano particles is proposed. It consists of two plasmonic nanorod arrays on top of two serial arms with quartz substrate. The operation principle is based on the absorbable formation of a conductive path in the dielectric layer of a plasmonic nanoparticle waveguide. Because the coherent perfect absorption efficiency depends strongly on the number of plasmonic nanorods and the locations of nanorods, an efficient binary optimization method based the Particle Swarm Optimization algorithm is used to design an optimized array of the plasmonic nanorods in order to achieve the maximum absorption coefficient in the ‘off’ state and the minimum absorption coefficient in the ‘on’ state. In Binary Particle Swarm Optimization, a group of birds consists a matrix with binary entries, control the presence (‘1’) or the absence (‘0’) of nanorods in the array. Copyright © 2016 John Wiley & Sons, Ltd.

Investigating the optical AND gate using plasmonic nano-spheres

In this paper, a coherent perfect absorption (CPA)-type AND gate based on plasmonic nano particles is proposed. It consists of two gold nano sphere arrays on top of two serial arms with quartz substrate. The operation principle is based on the absorbable formation of a conductive path in the dielectric layer of a plasmonic nano-particle waveguide. Since the CPA efficiency depends strongly on the number of gold nano-sphere and the locations of nano-spheres, an efficient binary optimization method based the Particle Swarm Optimization (PSO) algorithm is used to design an optimized array of the plasmonic nano-sphere in order to achieve the maximum absorption coefficient in the `off' state and the minimum absorption coefficient in the `on' state. In Binary PSO, a group of birds consists a matrix with binary entries, control the presence (`1') or the absence (`0') of nano sphere in the array.

Noise-immune cavity-enhanced optical heterodyne molecular spectrometry on N₂O 1.283 μm transition based on a quantum-dot external-cavity diode laser.

To access the wavelength within the 1.1-1.3 μm region, we have developed a quantum-dot (QD) laser with an external-cavity configuration and a linewidth of kilohertz at a 1 ms integration time. The residual electroluminescence, due to the inhomogeneous broadening of the QD gain medium, was observed and filtered out using a grating. While a fiber-coupled electro-optical modulator was employed, this laser system was locked to a high-finesse (F∼18,500) optical cavity, and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy was used to observe weak transitions. The Doppler-broadened spectra of a weak N(2)O transition at 1.283 μm are obtained with a signal-to-noise ratio of 30 for a gas pressure of 54 mTorr. The minimum noise-equivalent absorption coefficient is 5.3×10(-10) cm(-1) Hz(-1/2). This system can be a powerful and stable light source for atomic parity nonconservation measurements using thallium, ytterbium, lead, and iodine.