Determination Of Absorption Coefficient Research Articles

Density, ultrasound velocity, acoustic impedance, reflection and absorption coefficient determination of liquids via multiple reflection method

The accuracy of density, reflection coefficient, and acoustic impedance determination via multiple reflection method was validated experimentally. The ternary system water–maltose–ethanol was used to execute a systematic, temperature dependent study over a wide range of densities and viscosities aiming an application as inline sensor in beverage industries.The validation results of the presented method and setup show root mean square errors of: 1.201E−3gcm−3 (±0.12%) density, 0.515E−3 (0.15%) reflection coefficient and 1.851E+3kgs−1m−2 (0.12%) specific acoustic impedance. The results of the diffraction corrected absorption showed an average standard deviation of only 0.12%. It was found that the absorption change shows a good correlation to concentration variations and may be useful for laboratory analysis of sufficiently pure liquids.The main part of the observed errors can be explained by the observed noise, temperature variation and the low signal resolution of 50MHz. In particular, the poor signal-to-noise ratio of the second reflector echo was found to be a main accuracy limitation. Concerning the investigation of liquids the unstable properties of the reference material PMMA, due to hygroscopicity, were identified to be an additional, unpredictable source of uncertainty. While dimensional changes can be considered by adequate methodology, the impact of the time and temperature dependent water absorption on relevant reference properties like the buffer’s sound velocity and density could not be considered and may explain part of the observed deviations.

Determination of absorption coefficient based on laser beam thermal blooming in gas-filled tube

Thermal blooming of a laser beam propagating in a gas-filled tube is investigated both analytically and experimentally. A self-consistent formulation taking into account heating of the gas and the resultant laser beam spreading (including diffraction) is presented. The heat equation is used to determine the temperature variation while the paraxial wave equation is solved in the eikonal approximation to determine the temporal and spatial variation of the Gaussian laser spot radius, Gouy phase (longitudinal phase delay), and wavefront curvature. The analysis is benchmarked against a thermal blooming experiment in the literature using a CO₂ laser beam propagating in a tube filled with air and propane. New experimental results are presented in which a CW fiber laser (1 μm) propagates in a tube filled with nitrogen and water vapor. By matching laboratory and theoretical results, the absorption coefficient of water vapor is found to agree with calculations using MODTRAN (the MODerate-resolution atmospheric TRANsmission molecular absorption database) and HITRAN (the HIgh-resolution atmospheric TRANsmission molecular absorption database).

Predicted sound absorption coefficients of absorber materials lined in a chamber

Aims: The present study was aimed to measurement of sound absorption coefficient of mineral wool and determination of their absorption ability. Materials and Methods: Mineral wool was used to find noise absorption coefficient. Random and normal sound absorption coefficient values were predicted. Then, the measures of transmission loss calculated as an overall value, for applied absorbent material and bare sheet metal. Results: The measured values of noise with one octave band frequency demonstrated an attenuation of 5.5-7 dB for these frequencies. The absorption coefficients of materials showed that mineral wool had more normal sound coefficients than its random sound absorption coefficient values. Conclusion: It can be concluded that predicted normal sound absorption coefficients of used mineral wool materials were near to the areas of standard line. It seems that the amount or thickness of absorbent lining was a main reason of noise reduction in low band frequencies. Mineral wool has a higher density and can provide better acoustical and insulating results than fiberglass. Besides, mineral wool doesn't lose its insulating value when wet and has an outstanding resistance to fire.

Cavity mode-width spectroscopy with widely tunable ultra narrow laser

We explore a cavity-enhanced spectroscopic technique based on determination of the absorbtion coefficient from direct measurement of spectral width of the mode of the optical cavity filled with absorbing medium. This technique called here the cavity mode-width spectroscopy (CMWS) is complementary to the cavity ring-down spectroscopy (CRDS). While both these techniques use information on interaction time of the light with the cavity to determine absorption coefficient, the CMWS does not require to measure very fast signals at high absorption conditions. Instead the CMWS method require a very narrow line width laser with precise frequency control. As an example a spectral line shape of P7 Q6 O₂ line from the B-band was measured with use of an ultra narrow laser system based on two phase-locked external cavity diode lasers (ECDL) having tunability of ± 20 GHz at wavelength range of 687 to 693 nm.

Bandgap widening in thermochromic Mg-doped VO2 thin films: Quantitative data based on optical absorption

Thermochromic Mg-doped VO2 films were deposited by reactive direct current magnetron sputtering onto heated glass and carbon substrates. Elemental compositions were inferred from Rutherford backscattering. Optical bandgaps were obtained from spectral transmittance and reflectance measurements—from both the film side and the back side of the samples—and ensuing determination of absorption coefficients. The bandgap of Mg-doped films was found to increase by 3.9 ± 0.5 eV per unit of atom ratio Mg/(Mg + V) for 0 < Mg/(Mg + V) < 0.21. The presence of ∼0.45 at. % Si enhanced the bandgap even more.

Spectral reflectance of solar light from dirty snow: a simple theoretical model and its validation

Abstract. A simple analytical equation for the snow albedo as the function of snow grain size, soot concentration, and soot mass absorption coefficient is presented. This simple equation can be used in climate models to assess the influence of snow pollution on snow albedo. It is shown that the squared logarithm of the albedo (in the visible) is directly proportional to the soot concentration. A new method of the determination of the soot mass absorption coefficient in snow is proposed. The equations derived are applied to a dusty snow layer as well.

Flow-through PSICAM: a new approach for determining water constituents absorption continuously

Determination of spectral absorption coefficients in seawater is of interest for biologic oceanographers for various reasons, but faces also several problems, especially if continuous measurements are required. We introduce the flow-through point-source integrating cavity absorption meter (ft-PSICAM) as a new tool for the continuous measurement of spectral absorption coefficients in a range of 400–710 nm. A description of the system is given and its performance in comparison with a conventional PSICAM has been evaluated on two cruises in 2011 in the southern part of the North Sea (German Bight). Furthermore, factors influencing the measurement are discussed. When comparing the data of both systems, a good linear correlation has been found for all wavelengths (r 2 > 0.91). Deviations between systems were different with respect to the wavelength examined with slopes of linear fits between 1.1 and 1.65 and offsets between −0.1 and 0.01, with the higher values at shorter wavelengths. They were caused mainly due to contamination of the flow-through system during operation by phytoplankton particles. Focus was also laid on the measurement of chlorophyll-a concentrations ([chl-a]) and total suspended matter concentrations ([TSM]) on the basis of absorption coefficient determination. For this, appropriate relationships were established and [chl-a] and [TSM] values were calculated from the relevant ft-PSICAM absorption coefficients. Their progression matches well with the progression of fluorescence and turbidity measurements made in parallel. In conclusion, the ft-PSICAM is successful in measuring spectral absorption coefficients continuously and resolving relative changes in seawater optical properties.

Method of Testing of Sound Absorption Properties of Materials Intended for Ultrasonic Noise Protection

Abstract Efficient ultrasonic noise reduction by using enclosures requires the knowledge of absorbing properties of materials in the frequency range above 4 kHz. However, standardized methods enable determination of absorption coefficients of materials in the frequency range up to 4 kHz. For this reason, it is proposed to carry out measurements of the sound absorption properties of materials in the free field by means of a tone-burst technique in the frequency range from 4 kHz to 40 kHz at angles of incidence varying from 0° to 60°. The absorption coefficient of a material is calculated from the reflection coefficient obtained by reflecting a tone-burst from both a perfectly reflecting panel and a combination of this panel and the sample of the tested material. The tests results show that mineral wool and polyurethane open-cell foam possess very good absorbing properties in this frequency range.

A model for partitioning the light absorption coefficient of suspended marine particles into phytoplankton and nonalgal components

We developed a model for partitioning the spectral absorption coefficient of suspended marine particles, ap(λ), into phytoplankton, aph(λ), and nonalgal, ad(λ), components based on the stacked‐constraints approach. The key aspect of our model is the use of a set of inequality constraints that account for large variability in the aph(λ) and ad(λ) coefficients within the world's oceans. The bounds of inequality constraints were determined from the analysis of a comprehensive set of 505 field determinations of absorption coefficients in various oceanic environments. The feasible solutions of the model are found by simultaneously satisfying all inequality constraints. The optimal solutions represented by the median values of feasible solutions for aph(λ) and ad(λ) generally agree well with field measurements and are superior in terms of error statistics compared with previous partitioning models. For example, on the basis of comparisons of optimal model solutions with field determinations of absorption coefficients, the systematic error calculated as the median ratio of model‐derived to measured values for both aph(443) and ad(443) is within ±1% for our model. The random error represented by the mean absolute percent difference for aph(443) and ad(443) is <5% and <20%, respectively. This study suggests that our model has the potential for successful applications with input data of ap(λ) which can be collected from various oceanographic platforms.

Experimental Determination of Sound Absorption Coefficients of Four Types of Malaysian Wood

Currently, one of the important topics in acoustic science is noise control. It is important to control the noise in order to minimize extraneous noise in rooms, buildings, and our environment. Noise control can be achieved by reducing the intensity of sound to the level that is not harmful to human ear. There are four basic principles employed to reduce noise which is absorption, isolation, vibration isolation, and vibration damping. In fact, the most recognized technique to reduce noise is sound absorption on the materials itself. Sound absorption on material such as wood and porous material have been developed and studied by few researchers. Materials that reduce the sound intensity as the sound wave passes through it by the phenomenon of absorption are called sound absorptive materials. There are lot of methods can be used on determining the sound absorption coefficient of materials. In this paper, a preliminary work has been carried out experimentally to determine the sound absorption coefficient of four types of Malaysian wood. They are Tapang (Koompassia excels), Pulai (Alstonai angustiloba), Selunsor merah (Tristianiopsis beccariana) and Jelutong (Dyera polyphylla). The test was performed using the ASTM E1050-98/ISO 10534-2 (American Society for Testing and Material) standards for the sound absorption coefficient testing. This method is known as impedance tube method (Two-Microphone Method). The absorption coefficient depends on the frequencies. In this study the values of the frequencies used was in the range from 350 Hz to 1000 Hz.

Quantitative Analysis of IR Intensities of Alkanes Adsorbed on Solid Acid Catalysts

The goal of this work was to determine the integrated molar absorption coefficients of adsorbate vibrations and to use them as a measure of the activation of chemical bonds by the catalyst surface. For this purpose, an apparatus was built for the simultaneous measurement of transmission IR spectra of the adsorbate and the corresponding adsorption isotherm; the adsorbed amount was determined by a volumetric–barometric method. The adsorption of n-butane and 2,2-dimethylpropane on self-supporting wafers of mordenite and sulfated zirconia samples was investigated at temperatures of 298–308 K and alkane pressures of 0–100 hPa. The linear range of plots of the IR band intensities vs coverage was used to determine absorption coefficients of C–H stretching vibrations. The coefficients were found to depend on particle size and morphology, and it is shown that they are overestimated because the path length is enhanced through strong scattering in the wafers. The results reveal the limitations of quantitative analysis by transmission IR spectra when fine powders (such as catalysts) are investigated.

Accurate determination of optical nonlinear absorption coefficients by the combination of reflection and transmission open-aperture z-scan measurements

In most z-scan measurements, the Fresnel reflection loss is generally negligible, which is reasonable for transparent samples or materials with small nonlinear coefficients. However, for semi-transparent samples with low transmission or samples with large nonlinear coefficients, the Fresnel reflection loss attributed to the nonlinear effect is large and must be considered in z-scan measurement and data fitting. In this study, we proposed a method and established the corresponding theoretical model and experimental configuration of combining the reflection open-aperture z-scan and the transmission open-aperture z-scan measurements to determine accurately the nonlinear absorption coefficients by considering the Fresnel reflection loss. The Sb2Te3 film was used as an example. The nonlinear absorption coefficient was experimentally measured and theoretically fitted by our model. The theoretical fitting curves are highly consistent with the experimental data, indicating that the theoretical model and the configuration of the experimental setup can reasonably and feasibly obtain an accurate nonlinear absorption coefficient in actual applications.

Monochromatic computed tomography with a compact laser-driven X-ray source

A laser-driven electron-storage ring can produce nearly monochromatic, tunable X-rays in the keV energy regime by inverse Compton scattering. The small footprint, relative low cost and excellent beam quality provide the prospect for valuable preclinical use in radiography and tomography. The monochromaticity of the beam prevents beam hardening effects that are a serious problem in quantitative determination of absorption coefficients. These values are important e.g. for osteoporosis risk assessment. Here, we report quantitative computed tomography (CT) measurements using a laser-driven compact electron-storage ring X-ray source. The experimental results obtained for quantitative CT measurements on mass absorption coefficients in a phantom sample are compared to results from a rotating anode X-ray tube generator at various peak voltages. The findings confirm that a laser-driven electron-storage ring X-ray source can indeed yield much higher CT image quality, particularly if quantitative aspects of computed tomographic imaging are considered.

Determination of absorption coefficients for chlorophyll a, phycocyanin, mineral matter and CDOM from three central Indiana reservoirs

Absorption coefficients are used in semi-empirical and bio-optical models to estimate various optically active constituents in water. This study determines the mass-specific absorption coefficients of chlorophyll a (a*chl), phycocyanin (a*pc), minerals (a*m), and chromophoric dissolved organic matter (CDOM; a*CDOM) and the absorption coefficient for CDOM (aCDOM) for three central Indiana reservoirs. Absorption spectra were collected using a Shimadzu spectrophotometer equipped with a Spectralon coated integrating sphere. Quantitative measurements from either fluorometric (chlorophyll a, phycocyanin, CDOM) or weight-based (mineral) measurements were used to determine the mass-specific absorption coefficients tested in this study and an exponential function was used to estimate aCDOM. While a*chl showed minimum variability between reservoirs, a*pc, a*m, a*CDOM, and aCDOM showed statistically significant differences between reservoirs; however, for a*m, there was greater variation within each reservoir. Variability in a*CDOM and aCDOM between reservoirs was likely due to different inflows. All absorption coefficients fell within previously published ranges for each constituent examined, with the exception of a*pc. Differences in a*pc were likely due to different techniques used in extracting and estimating phycocyanin.

Spatially resolved collective excitations of nano-plasmas via molecular dynamics simulations and fluid dynamics

Collective excitations in nano-plasmas are described by dynamical bi-local auto-correlation functions. These excitations, which are related to the plasmon excitations in bulk plasmas, arise in the classical as well as the quantum regime. Instead of the wave-vector-dependent dynamical structure factor, which is not well defined in finite systems, two different signatures are considered to characterize collective excitations: the bi-local particle density correlation function and the bi-local current density correlation function. The relation between both signatures is not as trivial as in the homogeneous case and is given here. Exemplary calculations are performed for expanding nearly spherical clusters of sodium atoms after excitation by a high-intensity short pulse laser beam. The lowest collective excitations obtained in the classical regime using molecular dynamics simulations agree well with the lowest collective excitations obtained from quantum calculations using fluid dynamics. The energy, damping and structure of the lowest collective modes are given. The dynamical bi-local correlation functions are of relevance for the optical properties, in particular the determination of photo absorption coefficients of nano-plasmas.

A simple analysis of interband absorption in quantum well structure of III-V ternary and quaternary semiconductors

A simple generalized theory is presented for the determination of interband optical absorption coefficient (IOAC) around band edges, in quantum well (QW) structure of non-parabolic semiconducting materials whose band structures obey the three band model of Kane. The dependence of absorption coefficient on wave-vector (k→) has also been investigated. IOAC has been calculated for a wide range of III–V compound semiconductors, such as InAs, InSb, Hg1−xCdxTe, and In1−xGaxAsyP1−y lattice matched to InP. It has been found that IOAC for QWs increases in steps with increasing photon energy and the positions of jumps of the coefficient are more closely spaced in the three band model of Kane than those with parabolic energy band approximations in all the cases. IOAC for QWs is largely dependent on the polarization direction of the incident light and on the well dimension as well. The expressions of IOAC presented in this article can easily be extended to incorporate the effects of different external conditions like strain, electric, and magnetic fields on IOAC. It has also been shown that under certain limiting conditions the expressions for IOAC reduces to the previously known results for wide band gap materials and this is the indication for it to be a generalized theory for IOAC.

Absorption of acrylates and polysilazanes in the far UVC and the VUV regions

A simple but reliable method was developed for the determination of wavelength-dependent absorption coefficients in the vacuum-UV (VUV) spectral range 160 nm < λ < 195 nm. Absorption coefficients were determined on thin layers of UV curable compounds like acrylates and of polysilazanes, which are subject to photo-induced conversion into SiOx layers. Results were discussed in terms of changing values of the absorption coefficients during irradiation. In case of acrylates polymerization leads to the decrease of the absorption coefficients especially in the wavelength range about 195 nm from about 10 μm−1 to about 1 μm−1. Results of quantum-chemical calculations explain this finding by the depletion of double bonds for which ππ* transitions are characteristic. XPS depth profiles reveal the VUV induced degradation of carboxyl and ether functionalities in a thin surface layer corresponding to the penetration depth of the VUV photons.

Determination of optical absorption coefficient with focusing photoacoustic imaging

Absorption coefficient of biological tissue is an important factor for photothermal therapy and photoacoustic imaging. However, its determination remains a challenge. In this paper, we propose a method using focusing photoacoustic imaging technique to quantify the target optical absorption coefficient. It utilizes the ratio of the amplitude of the peak signal from the top boundary of the target to that from the bottom boundary based on wavelet transform. This method is self-calibrating. Factors, such as absolute optical fluence, ultrasound parameters, and Grüneisen parameter, can be canceled by dividing the amplitudes of the two peaks. To demonstrate this method, we quantified the optical absorption coefficient of a target with various concentrations of an absorbing dye. This method is particularly useful to provide accurate absorption coefficient for predicting the outcomes of photothermal interaction for cancer treatment with absorption enhancement.

Determination of total x-ray absorption coefficient using non-resonant x-ray emission

An alternative measure of x-ray absorption spectroscopy (XAS) called inverse partial fluorescence yield (IPFY) has recently been developed that is both bulk sensitive and free of saturation effects. Here we show that the angle dependence of IPFY can provide a measure directly proportional to the total x-ray absorption coefficient, µ(E). In contrast, fluorescence yield (FY) and electron yield (EY) spectra are offset and/or distorted from µ(E) by an unknown and difficult to measure amount. Moreover, our measurement can determine µ(E) in absolute units with no free parameters by scaling to µ(E) at the non-resonant emission energy. We demonstrate this technique with measurements on NiO and NdGaO3. Determining µ(E) across edge-steps enables the use of XAS as a non-destructive measure of material composition. In NdGaO3, we also demonstrate the utility of IPFY for insulating samples, where neither EY or FY provide reliable spectra due to sample charging and self-absorption effects, respectively.

A portable fiber optic system for measuring particle absorption using the quantified filter technique (QFT)

The Quantitative Filter Technique (QFT) has been shown to be an effective method for determining absorption coefficients of aquatic particles retained by filters. Although many investigators use the QFT, its routine use has been limited due in‐part to the required use of a high performance spectrophotometer and prescribed protocols for handling, storage, and transport of filters obtained in the field for later laboratory analysis. We describe a portable fiber optic system for conducting QFT measurements designed to overcome these limitations. The system (QFT2) consists of a high intensity light source, filter holder, and a photodiode array spectrometer configured as a single‐beam optical system. A set of 52 samples consisting of natural samples and cultures were analyzed following standard QFT protocols on a conventional spectrophotometer and the QFT2 system. Optical Density (absorbance) rather than absorption spectra were compared to avoid errors introduced by determining the pathlength amplification factor, β. Optical density (OD) spectra normalized at 400 nm measured using the fiber optic system were very similar to spectrophotometer spectra over a wide range of particle loadings. Strong linear relationships of normalized OD values at 443, 520, 550, 650, and 670 nm were observed for total particulate (r2 = 0.996; P &lt; 0.001, n = 52), detrital particulate (r2 = 0.991, P &lt; 0.001, n = 38), and pigmented particles or phytoplankton (r2 = 0.968, P &lt; 0.001, n = 38). The greatest difference between the two systems was observed at ca. 683 nm where the QFT2 underestimates absorption due to pigment fluorescence.