Showing papers on "Absorption (electromagnetic radiation) published in 1986"

Absolute absorption cross sections of ozone in the 185- to 350-nm wavelength range

Abstract: The absorption cross sections of ozone have been measured in the wavelength range 185-350 nm and in the temperature range 225-298 K. The absolute ozone concentrations were established by measuring the pressure of pure gaseous samples in the 0.08to 300-torr range, and the UV spectra were recorded under conditions where less than 1 percent of the sample decomposed. The temperature dependence is significant for wavelengths longer than about 280 nm. The absorption cross-section values around 210 nm were found to be about 10 percent larger than the previously accepted values.

Optical band gap of indium nitride

Abstract: Room‐temperature optical absorption data in the 1.5–2.5‐eV range are reported for indium nitride thin films prepared by reactive radio‐frequency sputtering. The fundamental absorption edge in high‐purity material is located at 1.89±0.01 eV and corresponds to a direct transition at k=0, in agreement with band‐structure calculations. A significant Moss‐Burstein shift is noted for carrier concentrations in excess of 1019 cm−3 and obeys the empirical relationship EG =1.89+2.1×10−8 n1/3 eV.

Comparison of x-ray absorption with x-ray photoemission of nickel dihalides and nio

Abstract: High-resolution ${L}_{2}$,3 x-ray absorption data are presented for nickel dihalides and nickel oxide. The near-edge multiplet splitting is observed to decrease rapidly with decreasing anion electronegativity. This decrease is accompanied by an increase in a satellite feature. A detailed analysis of the data in terms of recently proposed many-body theories is presented and is shown to yield excellent agreement with experiment allowing a determination of the charge-transfer energy, the d-d Coulomb interaction, and the Ni d--anion p hybridization interaction. We show that the values obtained are in good agreement with those obtained from x-ray photoelectron spectroscopy even though the spectral shapes are strongly different. The difference in spectral shapes is shown to be due to the very different final states.

A very singular solution of the heat equation with absorption

Abstract: Consider the Cauchy problem ut -du + u p ----0 on RN• (0, oo) (I.1) u > 0 on RN• (0, oo) (1.2) u(X, O) = c ~(x) on R, N, (1.3) where N _--> 1, c > 0 is a constant and ~(x) denotes the Dirac mass at the origin. A result of BREZlS and FRIEDMAN [6] asserts that if 1 < p < (N + 2)/N, then for every c > 0 there exists a unique 1 solution uc of (1.1)-(1.3). When p >= (N + 2)IN there is no solution of (1.1)-(1.3) and in fact any solution u of (1.1) such that u ~ 0 on RN• oo) and lim f u(x, t) Z(x) dx = 0 VT, ~ Co~ N \\ (0}) t~,o RN

Vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8

Abstract: The vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8 are reported for the wavelength region 107–220 nm using synchrotron radiation as a light source. Absorption maxima of these compounds were found at the exciting wavelengths of 115–119 nm. Broad peaks observed were mostly assigned as primarily Rydberg transitions of the σSiH and σSiSi bonding electrons to the 4s, 4p, and 4d orbitals. The absorption features of germane resemble those of monosilane. In the photoexcitation of monosilane, the emission of the SiH(A 2Δ→X 2Π) transition was observed and its onset was found to be 132±2nm. The absorption spectrum of disilane showed five peaks. They were mostly assigned as 2a1g→4s, 2a1g→np(n=4−6) transitions and the strongest band was overlapped by 1eg→4d and 1eu→4p Rydberg transitions. In trisilane molecules three very weak and broad peaks were recognized and assigned as 3b2→4s, 4p and 4a1→4s, 4d Rydberg transitions. The strongest band was tentatively assigned as the superposition of...

Collison-induced rototranslational absorption spectra of H2-He pairs at temperatures from 40 to 3000 K

Abstract: The zeroth, first, and second spectral moments of the rototranslational collision-induced absorption (RT CIA) spectra of hydrogen-helium mixtures are calculated from the fundamental theory, for temperatures from 40 to 3000 K. With the help of simple analytical functions of three parameters and the information given, the RT CIA spectra of H2-He pairs can be generated on computers of small capacity, with rms deviations from exact quantum profiles of not more than a few percent. Such representations of the CIA spectra are of interest for work related to the atmospheres of the outer planets and cool stars. The theoretical spectra are in close agreement with existing laboratory measurements at various temperatures from about 77 to 3000 K.

Eigenstate‐free, Green function, calculation of molecular absorption and fluorescence line shapes

Abstract: Green function techniques are used to develop a simple and efficient method towards the calculation of optical absorption, excitation, and dispersed fluorescence spectra of large harmonic polyatomic molecules. The molecular line shapes are expressed in terms of Fourier transforms of appropriate correlation functions which may be explicitly evaluated. Closed expressions are derived for a general harmonic molecule with two electronic states including equilibrium displacements, frequency changes, and Dushinsky rotation, within the Condon approximation. A simple method for extracting the complete set of parameters characterizing the ground and the electronically excited states from supersonic beam absorption and emission spectra is presented. Detailed calculations are performed for a model system with ten vibrational modes, and the sensitivity of the various experimental observables to Dushinsky rotation is analyzed.

Photoelectrochemistry in particulate systems. 4. Photosensitization of a titanium dioxide semiconductor with a chlorophyll analog

Abstract: Chlorophyllin, an analogue of chlorophyll a, when adsorbed on colloidal TiO/sub 2/ can participate in the sensitization process by injecting electrons from its excited states into the conduction band of the semiconductor. Upon excitation in its absorption band, 90% of the fluorescence emission of chlorophyllin could be quenched by colloidal TiO/sub 2/. The apparent association constant for the association between colloidal TiO/sub 2/ and chlorophyllin, as measured from the fluorescence quenching data, was 2 x 10/sup 4/ M/sup -1/. Picosecond lifetime measurements gave the rate constant for the electron injection process from the excited singlet state into the conduction band of the semiconductor as 4.2 x 10/sup 9/ s/sup -1/. The net charge transfer across the sensitizer-semiconductor interface was investigated with the laser flash photolysis and time-resolved microwave absorption techniques. Analysis of the transient absorption spectrum confirmed the generation of the cation radical of chlorphyllin with a quantum yield of 0.015. 32 references, 8 figures, 1 table.

Heating of the solar corona by the resonant absorption of Alfven waves

Abstract: An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. The primary conclusion to be drawn from these calculations is that to the level of the approximation adopted, the observations of the heating rate and nonthermal line broadening in the solar corona are consistent with heating by the resonance absorption mechanism.

Microwave Emission and Plant Water Content: A Comparison between Field Measurements and Theory

Abstract: Microwave radiation from a canopy cover depends primarily on the vegetation's thermal and dielectric properties; the latter are dependent on plant biometrical parameters and water content. Emission measurements carried out by means of ground-based X-and Ka-band radiometers have shown that crop coverage of soil can be detected through the spectral signatures of bare soil and vegetation. Moreover, measured brightness temperature and the radiative transfer theory for a scattering medium allow estimation of the scattering and absorption properties of the canopy. These parameters have been computed for corn and alfalfa using experimental data and a simple model in which anisotropic scattering is considered by means of transformed parameters w' and r'. We found that the single scattering albedo w' is always lower than 0.1, whereas the optical depth T' is very high. The latter has been correlated to plant water content by means of a logarithmic function.

Simultaneous measurement of the two-photon coefficient and free-carrier cross section above the bandgap of crystalline silicon

Abstract: We report what is to our knowledge the first simultaneous measurement of the two-photon absorption coefficient and the free-carrier cross section above the bandgap in a semiconductor. This is also the first observation of two-photon absorption of 1 μm radiation in single-crystal Si at room temperature in a regime where a two-photon stepwise process involving indirect absorption followed by free-carrier absorption is usually dominant. A critical pulsewidth (and fluence) is established below (and above) which two-photon absorption cannot be neglected. Pulses that range from 4 to 100 ps in duration are then used to isolate the irradiance-dependent two-photon absorption from the fluence-dependent free-carrier absorption. We obtain an indirect two-photon absorption coefficient of 1.5 cm/GW and extract a free-carrier cross section of 5 \times 10^{-18} cm2by using a simple technique that does not require a knowledge of the actual carrier density.

Fabrication and characterization of low-loss optical fibers containing rare-earth ions

Abstract: Low-loss fibers containing rare-earths have been produced with high absorption levels in the visible and near infrared regions. Although containing relatively large quantities of rare-earth impurity dopants, the fibers possess low-loss windows where the attenuation is similar to that observed in undoped fibers. This attribute makes the fibers attractive for use in long distributed sensors, as well as low-threshold fiber lasers. Fiber characteristics relevant to these two applications are uniformity of dopant incorporation, absorption and fluorescence spectra, and fluorescence lifetime. These measurements are presented, together with their respective temperature dependences. The fiber fabrication method is described and results given for Nd3+-, Er3+-, and Tb3+-doped fibers.

High-energy x-ray response of photographic films: models and measurement

Abstract: A detailed characterization has been established for the new, high-sensitivity double-emulsion Kodak Direct Exposure Film (DEF). The experimental data base consisted of density-versus-exposure measurements that were duplicated at several laboratories for x radiations in the 1000–10,000-eV region. The absorption and geometric properties of the film were determined, which, along with the density-exposure data, permitted the application of a relatively simple analytical model description for the optical density, D, as a function of the intensity, I (photons/μm2), the photon energy, E (eV), and the angle of incidence, θ, of the exposing radiation. A detailed table is presented for the I values corresponding to optical densities in the 0.2–2.0 range and to photon energies, E (eV), in the 1000–10,000-eV region. Experimentally derived conversion relations have been obtained that allow the density values to be expressed as either diffuse or specular. Also presented here is a similar characterization of the complementary, single-emulsion x-ray film, Kodak SB-5 (or 392). For the 1000–10,000-eV region this x-ray film is appreciably less sensitive but has higher resolution.

Optical constants of carbon dioxide ice

Abstract: Laboratory measurements of the absorption coefficient and refractive index of solid CO2 are reviewed for all parts of the electromagnetic spectrum from the ultraviolet to the microwave with emphasis on values for temperatures above 77 K The available measurements in some cases require reinterpretation A compilation of the spectral absorption coefficient kabs is made for 52-nm to 160-nm wavelength (with some gaps because of lack of data), and the complex refractive index is then computed by Kramers-Kronig analysis The uncertainty in imaginary refractive index is discussed; it varies greatly with wavelength The real part of the refractive index is close to 14 for all parts of the spectrum except near strong absorption bands and is accurate to ±005 outside those bands No measurements of absorption are available for 180–330-nm, 10–25-μm, and 25-μm–25-mm wavelength, except in the strong narrow absorption lines Remeasurement of kabs is also needed for parts of the IR spectrum between 25 and 25 μm because of experimental error in the available measurements

Effect of photosensitizer concentration in tissue on the penetration depth of photoactivating light

Abstract: The additional optical absorption in tissue resulting from the uptake of exogenous photosensitizers increases the effective attenuation of photoactivating light. This may be significant for the irradiation of solid tumours in photodynamic therapy, since it reduces the depth or volume of tissue treated. The effect has been studied in vitro by using dihaematoporphyrin ether (DHE) and 630 nm light in tissues representing a wide range of absorption and scattering conditions. While the attenuation may be markedly changed by small concentrations of DHE in pure scattering media, tissues with significant inherent light absorption are little affected by the additional absorption of DHE at concentrations relevant to clinical photodynamic therapy. However, it is shown that for other potential photosensitizers such as the phthalocyanines, which have substantially greater absorption at the treatment wavelength than DHE, the penetration of light in tissues may be significantly reduced.

Optical spectra and energy band structure of layer-type AIVBVI compounds

Abstract: The electroreflectance and absorption spectra as well as the hydrostatic pressure dependence of the fundamental absorption edge of GeS, GeSe, SnS, and SnSe crystals are investigated in polarized light. The lowest direct energy gaps are found to be 1V1—1V1 (E | | a) and 1Λ4—1Λ4 (E || b) for Ge and Sn monochalcogenides, respectively. The pressure coefficient of the energy gap 1Λ4—1Λ4 dE/AP = = — (1.3 ± 0.1) × 10−4 eV/MPa of SnSe and SnS is almost twice larger than that of the gap 1V1—1V1 in GeSe, GeS, and SnSe. On the basis of these investigations, different absorption mechanisms responsible for the fundamental absorption edge are discussed. [Russian Text Ignored].

Fiber optic probe system

Abstract: A system for automatic and real time detection of water and icing on surfaces by monitoring variations in light energy transmitted through an optical fiber having a specially processed sensitive area probe. The sensitive probe area is positioned on, about or within the surface on which icing is to be detected. Because of differences in optical indices of refraction and energy absorption characteristics of air, water and ice, the presence of each of these at the processed sensitive area will cause a proportional and characteristic attenuation of the light energy passing through the optical fiber. Changes in light energy transmission can be interpreted automatically to provide an indication of icing. A reference optical circuit may be used to provide compensation for variations in input energy levels. Light energy of different wave lengths and energy levels may be used to compensate for or avoid interference with measurement by ambient lighting conditions or for the detection of other conditions and materials using the principle of characteristic absorption and resonance.

Theoretical collision-induced rototranslational absorption spectra for the outer planets: H2-CH4 pairs

Abstract: The modeling of the collision-induced rototranslational absorption spectra for H2-CH4 molecules is described. The intermolecular potentials of the molecular complex are analyzed. The absorption coefficient is dependent on the molecular structure and the line-shape formulas for induction by hydrogen and methane are provided. Dipoles induced by an electric multipole field are examined. The measurements of the collision-induced absorption spectrum of the H2-CH4 system at 195 and 297 K are fitted to the Sutter et al. data. The relation between spectral components and H2-CH4 intermolecular potential are studied using the Hanley-Klein potential model (1972). Absorption coefficients of H2-CH4 are presented. 51 references.

Femtosecond carrier relaxation in semiconductor‐doped glasses

Abstract: Light induced changes of absorption in semiconductor‐doped glasses are studied on the femtosecond and picosecond time scale. Extremely rapid absorption recovery times of 200 fs are found when carriers are excited with large excess energy (500 meV) above the absorption edge of the semiconductor‐doped glasses. Excitation close to the band edge results in a slower absorption recovery with a time constant of τ≂100 ps.

Extended X-Ray Absorption Fine Structure

Abstract: The x-ray absorption spectrum of an atom exhibits sharp edges which correspond to the excitation threshold of the core electrons. If the atom is surrounded by other atoms in a condensed phase, then the absorption cross section above the absorption edge is observed to oscillate, exhibiting an often complex structure that can extend for hundreds of electron volts. These oscillations are aptly called the extended x-ray absorption fine structure (EXAFS). The fundamental understanding of EXAFS has advanced in the last two decades to the point where quantitative theoretical formulations can accurately account for the fine structure. The oscillations of the absorption cross section are due to the interference between the outgoing photoelectron wave and the incoming wave that is generated when the photoelectron scatters off of the atoms that surround the excited atom. Hence, EXAFS contains detailed information about the local environment of a particular type of atom. With the theoretical framework providing a relatively simple means of interpretation. EXAFS spectroscopy has developed into an important experimental tool for studying local atomic structure in solids.

Near-edge structure in electron-energy-loss spectra of MgO

Abstract: Electron-energy-loss spectra of all core-level absorption edges of MgO microcrystals were recorded in the transmission mode using 60-keV electrons. The low-noise signal attained at a resolution of 0.5 eV reveals details of fine structure in the near-edge region. The spectra obtained were analyzed by the application of multiple-scattering theory to the cluster model. For comparison, calculations of the projected density of states derived from Korringa-Kohn-Rostoker band structure are presented. An overall agreement between measurement and theory is achieved. Remaining deviations in details are discussed.

Sensor for measuring the concentration of a gaseous component in a fluid by absorption

Abstract: Apparatus and methods are provided for determining the concentration of a gaseous component in a fluid. A solid body of a natural or synthetic high polymer, which is permeable to the gaseous component, is exposed to the fluid, the polymer is exposed to infrared radiation, and the infrared absorption by the gas in the polymer is measured. In the preferred embodiment, a sensor is provided for making in vivo measurements of the concentration of CO2 in the blood. The sensor includes an optical fiber which is nonpermeable to CO2 and substantially transparent at the CO2 absorption wavelength range, and a solid body of polymeric material at the distal end of the fiber which is substantially transparent to the absorption wavelength range and permeable to CO2. An incident infrared signal is transmitted down the fiber, passes through the body, is reflected off the distal end of the body, and the intensity of the return signal is measured by a detector. The return signal is diminished in proportion to the concentration of the CO2 in the polymeric body. The sensor is disposed within a catheter and is positionable within the narrow blood vessels of the body for continuous real time monitoring of the carbon dioxide concentration of the blood.

Sulfur K-edge absorption spectra of Na2SO4, Na2SO3, Na2S2O3, and Na2S2Ox(x=5―8)

Abstract: X-Ray absorption spectra of the sulfur K-edges of SO42−, SO32−, S2O32−, and S2Ox2− (x=5–8) were measured with synchrotron radiation. The spectra show similarly strong absorption bands which originate in bound-state transitions to antibonding 3p-type orbitals and in shape resonances related to 3d-type orbitals. The K-edge spectrum for the terminal sulfur atom in S2O32−, however, shows only a bound-state transition. Differences in chemical environments and bonding around the X-ray absorbing atoms are discussed to interpret the spectra.

Optical recording medium

Abstract: PURPOSE:To prevent crosstalks by the light absorption generated between the optical recording layers of the optical recording medium used for a wavelength multiplex optical recording system by parting the wavelength widths between the absorption max. wavelengths of the optical recording layers by more than the half-amplitude level of the light absorption of the respective optical recording layers. CONSTITUTION:The optical recording layers subjected to recording in a heat mode have the energy threshold and the values thereof vary with the absorption wavelengths. The values are maximized at the absorption max. wavelength. The absorption does no longer change at all at the wavelength apart by more than the half-amplitude level of the absorption from the absorption max. wavelength by the photoirradiation of the energy value necessary for executing the sufficient recording at the absorption max. wavelength. The absorption max. wavelengths of the dyestuffs of the respective optical recording layers are, therefore, so selected as to be part by more than the half-amplitude levels thereof from the absorption max. wavelengths of the respective other optical recording layers, by which the crosstalks by the light absorption between the recording layers are prevented and the degree of wavelength multiplexing is increased.

Calculations of O2 absorption and fluorescence at elevated temperatures for a broadband argon—fluoride laser source at 193 nm

Abstract: Calculations have been made of O 2 absorption and fluorescence in the Schumann-Runge B 3 Σ - u ← X 3 Σ - g band system for excitation by a broadband argon fluoride excimer laser at 193 nm. Results are presented for line strengths, spectral absorption coefficients, relative fluorescence spectra, total fluorescence and integrated absorption coefficients. The calculations have been performed for 300, 500, 1000, 1500 and 2000 K, a range of temperatures typically found in combustion flows. The absorption coefficients and fluorescence yields found are large enough to encourage use of argon fluoride lasers for O 2 measurements in a variety of flows.

Detectors for liquid chromatography

Abstract: Refractive Index Detector Absorption Detectors for High-Performance Liquid Chromatography FTIR Detection Indirect Absorbance Detectors Fluorometric Detection Polarimetric Detectors Detection Based on Electrical and Electrochemical Measurements Mass Spectrometry as an On-Line Detector for HPLC Miscellaneous Methods Index.