Showing papers on "Absorption (electromagnetic radiation) published in 1982"
TL;DR: In this article, the authors adopt a statistical mechanical approach toward the optics of textured and inhomogeneous optical sheets and show that the local light intensity in such a medium will tend to be 2 n−2−x times greater than the externally incident light intensity, where n is the local index of refraction in the sheet.
Abstract: We adopt a statistical mechanical approach toward the optics of textured and inhomogeneous optical sheets. As a general rule, the local light intensity in such a medium will tend to be 2 n^{2}(x) times greater than the externally incident light intensity, where n(x) is the local index of refraction in the sheet. This enhancement can contribute toward a 4 n^{2}(x) increase in the effective absorption of indirect-gap semiconductors like crystalline silicon.
844 citations
01 Sep 1982
TL;DR: In this article, the authors adopt a statistical mechanical approach toward the optics of textured and inhomogeneous optical sheets and show that the local light intensity in such a medium will tend to be 2n/sup 2/(x) times greater than the externally incident light intensity, where n(x) is the local index of refraction in the sheet.
Abstract: The authors adopt a statistical mechanical approach toward the optics of textured and inhomogeneous optical sheets. As a general rule, the local light intensity in such a medium will tend to be 2n/sup 2/(x) times greater than the externally incident light intensity, where n(x) is the local index of refraction in the sheet. This enhancement can contribute toward a 4n/sup 2/(x) increase in the effective absorption of indirect-gap semiconductors like crystalline silicon. Also it may lead to a voltage increase equal to KTlog 4n/sup 2/.
800 citations
TL;DR: In this article, collapse characteristics and energy absorption of a variety of tubes made in glass, graphite and Kevlar fiber composites have been examined, and a critical range of tube geometry over which stable collapse occurred with high energy absorption; thinner wall tubes tended to collapse in an unstable manner with lower energy absorption.
Abstract: The collapse characteristics and energy absorption of a variety of tubes made in glass, graphite and Kevlar fiber composites have been examined. Tubes made from glass or graphite fibers collapsed by a fracture mode. There was a critical range of tube geometry over which stable collapse occurred with high energy absorption; thinner wall tubes tended to collapse in an unstable manner with lower energy absorption. Changes in the lay-up which increased the modulus increased the energy absorption of the tube. Tubes made from, or including Kevlar fiber, tended to collapse in an unstable mode by buckling rather than by fracture, which led to low values for specific energy absorption.
240 citations
TL;DR: In this paper, a simple model of laser light absorption is described and the absorption mechanism is mainly inverse bremsstrahlung, but a crude description of resonance absorption is also included.
Abstract: A simple model of laser light absorption is described. The absorption mechanism is mainly inverse bremsstrahlung, but a crude description of resonance absorption is also included. The intensity and the wavelength dependence are emphasized, but the model takes into account the target material composition, the laser pulse length, and the focal spot radius. Plane and spherical expansion are treated. Results range from short‐wavelength, low‐intensity regime, where inverse bremsstrahlung absorption is total, to long‐wavelength high‐intensity regime, where inverse bremsstrahlung absorption is negligible. Scaling laws concerning absorption, electron temperature, and electron kinetic pressure are given in the two limiting regimes. A characteristic flux Φ*, or, alternatively, a characteristic wavelength λ* is defined which separates the two regimes, the other parameters being held constant.
211 citations
TL;DR: For a multilayer structure illuminated by a laser beam, absorption of optical energy in the absorptive layers and the diffusion of the resultant heat throughout the structure are studied.
Abstract: For a multilayer structure illuminated by a laser beam, absorption of optical energy in the absorptive layers and the diffusion of the resultant heat throughout the structure are studied. Analytical and numerical procedures for this study are described, and, as a specific example, the profiles of temperature distribution during recording on a magnetooptical disk are presented. The technique is also expected to be of value for studies of thermal marking and laser annealing.
198 citations
TL;DR: In this article, a model experiment has been carried out to examine the effect of surface irregularity of an urban structure on the anomalous absorption of incident solar radiation, and the results show that the absorption increment originating from the irregular urban structure amounts to about 20% as compared with the absorption by a flat surface of the same material.
Abstract: A model experiment has been carried out in order to examine the effect of surface irregularity of an urban structure on the anomalous absorption of incident solar radiation. Several models of an urban structure resembling buildings and canyons were constructed by using concrete blocks in cubic form. By building and dismantling the urban models, the albedo change as a function of solar zenith angle was observed throughout the year. The result shows that the absorption increment originating from the irregular urban structure amounts to about 20% as compared with the absorption by a flat surface of the same material. The amount of additional absorption depends on the relative area occupied by canyons in the model.
176 citations
TL;DR: Tellinghuisen et al. as discussed by the authors reassessed the contributions of the 1Πu and A potentials and their diffuse absorption spectra to the absorption coefficient of I2 in the 4200-8000 A region.
Abstract: The contributions of the 1Πu←X, B←X, and A←X transitions to the absorption coefficient of I2 in the 4200–8000 A region are reassessed in light of recent results concerning the 1Πu and A potentials and their diffuse absorption spectra. Earlier estimates of the continuum underlying the B←X discrete spectrum are augmented by additional high‐resolution ’’between‐the‐lines’’ absorption measurements, corrected for residual B–X absorption using the very reliable spectroscopic constants now available for this system. The 1Πu–X and A–X systems are now estimated to be about 10% weaker than in the previous analysis [J. Tellinghuisen J. Chem. Phys. 58, 2821 (1973)]. For the region 2.6–2.8 A sampled in absorption, the estimates of the B–X transition strength ‖μe‖2 remain close to the previous values.
165 citations
TL;DR: In this article, a series of silicon dioxide (SiO2) films grown on silicon wafers from a HCl and O2 gas mixture at 850°C, have been studied for film thicknesses down to 28 A. The validity of Lambert Bouguer's Law for such thin films has been confirmed, and the apparent absorption coefficient calculated for the absorption at 1065 cm−1 is in good agreement with previously published data for thicker, vapordeposited, and thermally grown films.
Abstract: Infrared transmission spectra of a series of silicon dioxide (SiO2) films grown on silicon wafers from a HCl and O2 gas mixture at 850 °C, have been studied for film thicknesses down to 28 A. The validity of Lambert‐Bouguer’s Law for such thin films has been confirmed, and the apparent absorption coefficient calculated for the absorption at 1065 cm−1 is in good agreement with previously published data for thicker, vapor‐deposited, and thermally grown films. A continuous shift of the absorption near 1065 cm−1 has been found, moving from an asymptotic limit maximum of ∼1070 cm−1 for thick films towards smaller wave numbers for thinner films. Various possibilities for the origin of this shift are discussed.
164 citations
TL;DR: In this article, the authors describe the development of an aethalometer that can measure aerosol absortion in real time, which can be used for real-time analysis.
Abstract: The authors describe the development of an aethalometer. This portable device measures aerosol absortion in real time. (AIP)
157 citations
TL;DR: In this paper, the details of an iterative radiative transfer code for computing the intensity and degree of polarization of diffuse radiation in models of the ocean-atmosphere system are described.
Abstract: The details of an iterative radiative transfer code for computing the intensity and degree of polarization of diffuse radiation in models of the ocean-atmosphere system are described. The present code neglects the upwelling radiation from below the ocean surface and as such can be applied to the part of the spectrum where the absorption by water is strong. To establish the reliability of the numerical scheme and the computer code, the results are compared with those of Fraser and Walker (1968), Dave (1972), and Mullamaa (1964); they are found to be in excellent agreement. The computations also show that both the intensity and the degree of polarization of the upwelling diffuse radiation at the top of the atmosphere vary significantly when the rough ocean at the base of the atmosphere is replaced by a Lambertian surface that reflects the same energy as the rough ocean.
TL;DR: Calculations of photosynthetically usable radiation, the light an alga is capable of absorbing in its own submarine habitat, suggest that the algae at different depths are optimizing rather than maximizing their ability to harvest submarine light energy.
Abstract: Zooxanthellae living in colonies of the Caribbean reef coral Montastrea annularis photoadapt to depth-dependent attenuation of submarine light. Studies carried out at Discovery Bay, Jamaica, show that in shallow-living coral colonies, the zooxanthellae appear photoadapted to function at high light intensities, and do poorly if transplanted to low light intensities; in contrast, zooxanthellae in deeper-living coral colonies can be damaged by high light intensities. The adaptation to decreasing light intensity and changing spectral quality appears to be accomplished by increasing the size of the photosynthetic unit (PSU), as opposed to increasing the number of PSU's per cell. Whole cell absorption increases with depth, partially offsetting the loss of light energy due to depth-dependent attenuation. Calculations of photosynthetically usable radiation, the light an alga is capable of absorbing in its own submarine habitat, suggest that the algae at different depths are optimizing rather than maximizing their ability to harvest submarine light energy.
TL;DR: In this article, it was shown that the magnetic field convectively transports hot electrons and confine a major fraction of the deposited laser energy in the corona, which is lost to fast-ion blowoff or deposited at large distances from the spot.
Abstract: Electrons heated by absorption of laser energy are shown to generate intense magnetic fields which rapidly spread from the edge of the laser spot along the target surface. The fields convectively transport hot electrons and confine a major fraction of the deposited laser energy in the corona. Eventually, this energy is lost to fast-ion blowoff or deposited at large distances from the spot. This model qualitatively explains many experimental observations of thermal-transport inhibition and fast-ion loss.
TL;DR: In this article, an investigation of the Schottky barrier of a number of metals on natural P-type MoS 2 was undertaken, and the spectral dependence of the photovoltaic effect of all the metal barriers showed two distinct features at 1.38 and 1.68 eV below the direct bandgap at 2.8 eV.
TL;DR: In this paper, it was shown that absorbing blackbody radiation by Rydberg atoms in a resonant cavity is a collective process in which the atoms behave as a Bose gas and the equilibrium energy of this gas was measured and found equal to twice the photon energy.
Abstract: Absorption of blackbody radiation by Rydberg atoms in a resonant cavity is shown to be a collective process in which the atoms behave as a Bose gas. The equilibrium energy of this gas was measured and found equal to twice the photon energy (factor of 2 accounting for atomic transition degeneracy). It is shown that this experiment exhibits the Brownian motion of the atomic-system Bloch vector.
TL;DR: The measured lifetime of 39 (0) and 27 (N) nsec and quenching rate constants of 2.5 x 10(-10) cm(-3) sec(-1) for collisions of N(2) with each atom indicate promise for this method as a diagnostic tool in flames and plasmas.
Abstract: The 3p (3)P state of O and the 2s(2)2p(2)3p (4)D(0) states of N are populated by two-photon absorption at 226 and 211 nm, respectively, and the resulting near-IR fluorescence is detected. The exciting photons are provided by stimulated Raman frequency shifting, and the experiments are performed in a flow discharge. The measured lifetime of 39 (0) and 27 (N) nsec and quenching rate constants of 2.5 x 10(-10) cm(-3) sec(-1) for collisions of N(2) with each atom indicate promise for this method as a diagnostic tool in flames and plasmas.
TL;DR: By observing the decay in flight of laser-excited atoms in a fast atomic beam with energy between 60 and 150 keV, the lifetimes of the Li 2/sup 2/P/sub 1/2/ and Na 3/sup 1/1/2 ) were measured to be (27.29 +- 0.04) and (16.40 + − 0.03) nsec, respectively.
Abstract: By observing the decay in flight of laser-excited atoms in a fast atomic beam with energy between 60 and 150 keV, lifetimes of the Li 2/sup 2/P/sub 1/2/ and Na 3/sup 2/P/sub 1/2/ are measured to be (27.29 +- 0.04) and (16.40. +- 0.03) nsec, respectively (uncertainties are one standard deviation).
TL;DR: The optical absorption coefficient of silicon has been measured at the HeNe near-infrared line (λ = 1.152 μm) from room temperature to 1140 K as mentioned in this paper.
Abstract: The optical absorption coefficient of silicon has been measured at the HeNe near‐infrared line (λ = 1.152 μm) from room temperature to 1140 K. The results are compared with the previous less extensive data in the literature, and with the formulation given by Macfarlane et al. [Phys. Rev. 111, 1245 (1958)]. It is found that the absorption is described very well by phonon‐assisted indirect transitions across an energy gap having the temperature dependence described by Thurmond.
TL;DR: Seven types of error that may interfere with the analysis of protein circular dichroism (CD) spectra for secondary structure are examined and it is found that small errors in the baseline will rationalize poor analyses.
TL;DR: In this article, a 20μdiam dye-impregnated glycerol sphere has been observed at intensities as low as ∼ 1 W/cm2 in air at 30 Torr.
Abstract: Radiometric levitation of a 20‐μ‐diam dye‐impregnated glycerol sphere has been observed at intensities as low as ∼1 W/cm2 in air at 30 Torr. The levitation has been effected on both strongly absorbing spheres in the direction of the light and weakly absorbing spheres in the opposite sense. Both strongly and weakly absorbing spheres are found to laterally seek an intensity minimum. Consequently particles were stably held in the focused beam of an Ar+ laser (4880 A) operating in the TEM*01 (doughnut) mode.
TL;DR: In this article, high resolution infrared absorption and emission spectra have been obtained from an electrical discharge in silane, in addition to extracting vibrational and rotational temperatures for silane itself and emission from the ground electronic state of the free radical SiH.
Abstract: High resolution infrared absorption and emission spectra have been obtained from an electrical discharge in silane. In addition to extracting vibrational and rotational temperatures for silane itself, emission from the ground electronic state of the free radical SiH is observed and vibrational and rotational temperatures of 2000 and 485 K determined.
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01 Jun 1982TL;DR: In this article, the authors used cellulose microfibers with diameters ranging from about 0.01 microns to about 15 microns for fiber absorbent web construction.
Abstract: Fibrous absorbent webs having a low density (about 0.01 g/cm3 to about 0.15 g/cm3) and comprising at least about 50% hydrophilic microfibers, such as cellulose microfibers, having a diamter of from about 0.01 microns to about 15 microns possess superior absorption properties, especially under typical usage conditions. Hydrophobic microfibers may also be used, providing such fibers are hydrophilized before or after web formation.
TL;DR: In this paper, a set of solar irradiance observations from the third Solar Absorption Balloon Experiment (SABE-3) was analyzed and compared with calculations of attenuated irradiance based on simultaneous ozone and pressure measurements made from the payload.
Abstract: A set of solar irradiance observations is analyzed that were performed from the third Solar Absorption Balloon Experiment (SABE-3) as the payload ascended through the stratosphere from 32 to 39 km. Comparison of these data with calculations of the attenuated irradiance based on simultaneous ozone and pressure measurements made from the payload suggests a refinement of the cross section values used in photochemical models. More ultraviolet radiation in the 200-210 nm spectral region reaches the middle stratosphere than is predicted by the absorption data presently available. It is suggested that significantly smaller values for the Herzberg continuum of O2 be used in future models.
TL;DR: A new technique has been developed for determination of optical depths delta(a) as low as 0.0005 for thin layers of absorbing materials or particles, directed toward determination of the absorption coefficient of atmospheric aerosols in remote and relatively unpolluted locations.
Abstract: A new technique has been developed for determination of optical depths δa as low as 0.0005 for thin layers of absorbing materials or particles. The measurement involves optical amplification of the absorption and is not affected by the scattering properties of the absorber. This is accomplished by introducing the absorber into the virtually isotropic radiation field between two high-reflectance diffusing wafers and measuring the resultant attenuation of the transmitted light. The technique has been directed toward determination of the absorption coefficient of atmospheric aerosols in remote and relatively unpolluted locations. Provided appropriate collection filters and sampling conditions are used, the method can establish an absorption coefficient for the aerosol as low as 5 × 10−9 m−1 within a 10-h sampling period. A proportionally higher absorption coefficient requires proportionally less sample time. This paper discusses instrument design, the theoretical optical model, laboratory calibration, and a field test of the technique.
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TL;DR: The size and temperature, morphology and distribution, variability, possible absorption features, and processes of hot spots on Io are discussed, and an estimate of the global heat flux is made.
Abstract: The size and temperature, morphology and distribution, variability, possible absorption features, and processes of hot spots on Io are discussed, and an estimate of the global heat flux is made. Size and temperature information is deconvolved to obtain equivalent radius and temperature of hot spots, and simultaneously obtained Voyager thermal and imaging data is used to match hot sources with specific geologic features. In addition to their thermal output, it is possible that hot spots are also characterized by production of various gases and particulate materials; the spectral signature of SO2 has been seen. Origins for relatively stable, low temperature sources, transient high temperature sources, and relatively stable, high-tmperature sources are discussed.
TL;DR: In this paper, the performance and application of an ultrahigh vacuum compatible constant-deviation double-crystal monochromator (JUMBO) in operation at SSRL is demonstrated.
01 Mar 1982
TL;DR: In this article, the authors compared the H2O continuum absorption obtained by many different workers from laboratory samples and atmospheric paths in the various windows in the infrared, millimeter-wave and microwave regions.
Abstract: : Data on the H2O continuum absorption obtained by many different workers from laboratory samples and atmospheric paths are compared in the various windows in the infrared, millimeter-wave and microwave regions. Values of the continuum absorption coefficients calculated on the basis of simple, widely used line shapes may differ greatly from observed values in the windows between strong absorption lines. The temperature dependence of this absorption is also not predictable from present day understanding of line shapes or of dimers, which are thought by many to contribute. The shapes of self-broadened H2O lines are quite different from those of N2-broadened lines, and the difference increases with increasing distance from the centers of the lines. Several characteristics of the continuum absorption are common throughout the windows from the infrared to the microwave region. (Author)
TL;DR: In this article, the boundary conditions and the optical absorption are studied for both the discrete and the continuum models of solitions in polyacetylene, and the theoretical results are compared with the experimental data.
Abstract: In the present paper the boundary conditions and the optical absorption are studied for both the discrete and continuum models of solitions in polyacetylene. The topological property of the soliton is incorporated appropriately to derive the correct boundary conditions for the electronic wave functions which are essential for a proper calculation of optical absorption and other properties of the system. A general sum rule for the absorption coefficient is derived for the continuum model which is exactly satisfied by the result of the present calculation. The errors in the previous calculations are indicated. Finally, the theoretical results are compared with the experimental data.