Absorption (electromagnetic radiation)

About: Absorption (electromagnetic radiation) is a research topic. Over the lifetime, 76674 publications have been published within this topic receiving 1381221 citations.

Measurement of soft X-ray absorption spectra with a fluorescent ion chamber detector

Abstract: The problem of absorption of soft X-rays by thick Be windows in hard X-ray beam lines is well known. Although the signal at 2.4 keV was reduced by ∼ 103 we have routinely measured the absorption spectra of S (2472 eV) and elements at higher energies including Cl, Ar and K. These spectra were obtained on hard X-ray beam lines at Stanford Synchrotron Radiation Laboratory (SSRL) with Si(111) monochromator crystals and a fluorescent ion chamber detector [1]. Higher energy harmonics were minimized by detuning and the end station was enclosed in a helium bag to prevent absorption by air. Although the diminished X-ray flux and decreasing fluorescent yield were serious negative factors at these low X-ray energies the spectra from thick samples were of excellent quality with sufficient sensitivity to characterize 1% S in coal. Representative spectra are shown comparing data from focused and unfocused beam lines and with S data from JUMBO [2]. Comparison of Ar and KCl data to excellent data found in the older literature [3–5] allow a confirmation of the resolution function (energy bandpass) of the monochromator. A simple new beam line is suggested which would allow a substantial increase in low energy X-ray flux (measurements down to Al and Si) with the sample and detector in a He atmosphere.

Many-particle effects in the optical spectrum of a semiconductor

Abstract: A local-orbital treatment of the two-particle Green's function for the electron-hole interaction is presented which takes into account both screened electron-hole attraction and its exchange counterpart. They give rise to the excitonic effects including Frenkel and intermediate coupling regimes and to the random-phase approximation local-field effects, respectively. An alternative formulation based on the Kohn-Sham density-functional scheme is also given and numerically tested. Quantitative calculations of the absorption and modulation spectra in Si show that electron-hole interaction effects significantly modify the absorption line shape and give rise to shifts of critical-point structure up to 0.2 eV. A model analysis indicates that deviations of the one-particle spectra of column IV, III-V, and II-VI semiconductors from experiment should similarly be accounted for.

Study on the prediction of visible absorption maxima of azobenzene compounds

Abstract: The geometries of azobenzene compounds are optimized with B3LYP/6-311G* method, and analyzed with nature bond orbital, then their visible absorption maxima are calculated with TD-DFT method and ZINDO/S method respectively. The results agree well with the observed values. It was found that for the calculation of visible absorption using ZINDO/S method could rapidly yield better results by adjusting OWFπ-π (the relationship between π-π overlap weighting factor) value than by the TD-DFT method. The method of regression showing the linear relationship between OWFπ-π and BLN-N (nitrogen-nitrogen bond lengths) as OWF π-π=−8.1537+6.5638BL N-N, can be explained in terms of quantum theory, and also be used for prediction of visible absorption maxima of other azobenzne dyes in the same series. This study on molecules’ orbital geometry indicates that their visible absorption maxima correspond to the electron transition from HOMO (the highest occupied molecular orbital) to LUMO (the lowest unoccupied molecular orbital).

Strong 8.2 μm infrared intersubband absorption in doped GaAs/AlAs quantum well waveguides

Abstract: We have measured the infrared intersubband absorption at 8.2 μm in doped GaAs/AlAs quantum well superlattices. Waveguide geometry experiments demonstrate strong absorption with 95% of the incident infrared energy being absorbed.

Emission Factors and Real-Time Optical Properties of Particles Emitted from Traditional Wood Burning Cookstoves

Abstract: It is estimated that the combustion of biofuel generates 20% of all carbonaceous aerosols, yet these particles are studied less than those of other common sources. We designed and built a portable battery-operated emission-sampling cart to measure the real-time optical properties and other emission characteristics of biofuel cookstoves. In a field study in Honduras, we measured emission factors averaging 8.5 g/kg, higher than those found in previous laboratory studies. Strong flaming events emitted very dark particles with the optical properties of black particles. The elemental carbon to total carbon ratios ranged from 0.07 to 0.64, confirming that high elemental carbon fractions can be emitted from biofuel combustion and may not be used to distinguish fossil-fuel from biofuel sources when cooking is the dominant usage. Absorption Angstrom exponents, representing the dependence of absorption on wavelength, ranged from 1 (black) to 5 (yellow). Strongly absorbing particles with absorption inversely dependent on wavelength were emitted separately from particles with weak absorption and strong wavelength dependence; the latter probably contained conjugated aromatic compounds. Because combustion occurs in distinct phases, different types of carbonaceous aerosols from biofuel combustion are externally mixed at emission and may have different atmospheric fates.