Showing papers on "Absorption (electromagnetic radiation) published in 1979"
TL;DR: In this paper, the transition to single crystal of ion-implanted amorphous Si and Ge layers is described in terms of a liquid phase epitaxy occurring during pulsing-laser irradiation.
Abstract: The transition to single crystal of ion‐implanted amorphous Si and Ge layers is described in terms of a liquid‐phase epitaxy occurring during pulsing‐laser irradiation. A standard heat equations including laser light absorption was solved numerically to give the time evolution of temperature and melting as a function of the pulse energy density and its duration. The structure dependence of the absorption coefficient and the temperature dependence of the thermal conductivity were accounted for in the calculations. In this model the transition to single crystal occurs above a well‐defined threshold energy density at which the liquid layer wets the underlying single‐crystal substrate. Experiments were performed in ion‐implanted amorphous layers of thicknesses ranging between 500 and 9000 A. The energy densities of the Q‐switched ruby laser ranged between 0.2 and 3.5 J/cm2; time durations of 20 and 50 ns were used. The experimental data are in good agreement with the calculated values for the amorphous thickness–energy−density threshold. The model deals mainly with plausibility arguments and does not account for processes occuring in the near‐threshold region or below the melting temperature.
352 citations
TL;DR: In this article, the experimental dependence of electron mobility and free-carrier absorption on temperature and/or on carrier concentration can be consistently explained only when the effect of compensation is quantitatively taken into account.
Abstract: Theoretical and experimental studies of the electron mobility and the free‐carrier absorption of n‐type InP were carried out in the temperature range 77–300 °K. All major scattering processes and screening effects were taken into consideration. It was found that the experimental dependence of electron mobility and free‐carrier absorption on temperature and/or on carrier concentration can be consistently explained only when the effect of compensation is quantitatively taken into account. Convenient procedures are presented for the determination of the compensation ratio from the values of electron mobility and from the free‐carrier absorption coefficient. The high contribution of optical‐phonon scattering in InP limits the applicability of the free‐carrier absorption approach to electron concentration n≳1017 cm−3. Electron mobility, however, can be reliably employed for the determination of the compensation ratio for n≳1017 cm−3 at 300 °K and n≳1015 cm−3 at 77 °K.
315 citations
TL;DR: In this article, the LIII x-ray absorption threshold resonance of the elements iridium, platinum, and gold in the pure metallic state and in a variety of compounds was analyzed.
Abstract: We report spectra isolating the LIII x‐ray absorption threshold resonance of the elements iridium, platinum, and gold in the pure metallic state and in a variety of compounds. When normalized spectra obtained on the metals are subtracted from those obtained on the compounds, the resulting difference spectra are related to differences in the electronic structure of the absorber atom in the two types of environment. The change in area of a threshold resonance line obtained from such a difference spectrum can be related to the ionicity of the bonds of the absorber atom in its compounds. Measurements on supported platinum and iridium catalysts provide information on electronic changes in the metal due to the small size of the metal clusters or to interaction with the support material. Information on electronic changes due to interaction of the catalysts with gas molecules may also be obtained.
258 citations
Journal Article•
241 citations
TL;DR: In this article, the authors measured the optical absorption spectra of solvated electrons in H/sub 2/O and D/sub O and found that the spectrum at a given A/A/sub max/ shows a shift of +0.05 eV in the low-energy wing, reaching 0.03 eV at the absorption maximum.
Abstract: The optical absorption spectra of solvated electrons in H/sub 2/O and D/sub 2/O have been measured at 274, 298, 340, and 380 K. All the spectra were fitted very well with the Gaussian and Lorentzian shape functions at the low- and high-energy sides of the absorption maximum, respectively, excluding the high-energy tail. The spectrum does not shift uniformly with temperature. The temperature coefficient of absorption decreases rapidly with increasing energy on the low-energy side of the absorption maximum, while it changes only slightly on the high-energy side. When the temperature increases the Lorentzian width remains constant, the Gaussian width varies proportionally to T/sup 1/2/, and the spectrum becomes more symmetrical. On going from H/sub 2/O to D/sub 2/O we found that the spectrum at a given A/A/sub max/ shows a shift of +0.05 eV in the low-energy wing. The shift decreases with increasing energy, reaching 0.03 eV at the absorption maximum. On the high-energy side of the band the shift becomes negative at h..nu.. > 2.2 eV. The shift on the low-energy side seems to be related to the difference of the zero-point energies of the inter- and intramolecular vibrations. The wavelength dependence of the temperature and isotope effects ismore » consistent with the model that different types of excitation occur on the low- and high-energy sides of the absorption band. The temperature and isotopic dependence of the low-energy side are consistent with its width being due to phonon interactions.« less
215 citations
TL;DR: A pulsed dye-laser optoacoustic spectroscopy technique has been used to measure the absorption spectra of light and heavy water at 21.5 degrees C in the visible region and are believed to be the most reliable so far.
Abstract: A pulsed dye-laser optoacoustic spectroscopy technique has been used to measure the absorption spectra of light and heavy water at 21.5 degrees C in the visible region. Basic principles of pulsed optoacoustic spectroscopy technique and the procedure for absolute calibration are discussed with reference to its application in water. Experimental details of the application of optoacoustic spectroscopy to water are given. Our absorption coefficients, of accuracies about +/- 10%, are believed to be the most reliable so far. Light water has a broad absorption minimum near 475 nm where the absorption coefficient is 1.8 x 10(-4) cm(-1). Heavy water exhibits a totally different absorption spectrum and has a broad absorption minimum near 600 nm where the absorption coefficient is 1.9 x 10(-4) cm(-1). Previous measurements of the optical spectra of water were done mostly by long-path transmission measurements, and they display disagreement by factors as large as 10 near the green absorption minimum of light water. We give a critical comparison of our optoacoustic absorption spectra with other existing data.
202 citations
TL;DR: In this paper, the authors interpreted the absorption of AlN thin films as excitonic absorptions due to transitions across the direct energy gap of about 6.2 eV and 7.8 eV.
Abstract: Optical absorption of AlN thin films shows a ’’knee’’ structure at 6.2 eV and an intense band at 7.8 eV. The structure at 6.2 eV is interpreted as excitonic absorptions due to transitions across the direct energy gap of about 6.2 eV. Dichroism observed at the absorption edge indicates that the transition Γ1v–Γ1c (E∥c) is of lower energy than the transition Γ6v–Γ1c (E⊥c). Strong dichroism in the 7–8‐eV region is thought to cause the birefringence of AlN.
190 citations
01 Jan 1979
176 citations
TL;DR: In this paper, the optical properties of bulk and thin-film Zn3P2 have been measured at room temperature over the range 0.5-5.0 eV, with emphasis on the region of the interband absorption edge.
Abstract: The optical properties of bulk and thin‐film Zn3P2 have been measured at room temperature over the range 0.5–5.0 eV, with emphasis on the region of the interband absorption edge. The bulk absorption edge is found to be exponential in energy for values of absorption coefficient less than about 1500 cm−1. The thin‐film absorption edge, when freed of spurious absorptance due to scattering, is also found to be exponential over this range although shallower in slope. Analysis of the thin‐film data at higher values of absorption coefficient is inconclusive with respect to the nature of the edge. Nevertheless, indirect evidence suggests that the optical gap is probably direct and lies in the neighborhood of 1.6 eV. Measurements of refractive index in the near‐infrared yield n=3.3±0.1 in the long‐wavelength limit. The ultraviolet reflectivity spectrum is redetermined, and found to differ substantially from earlier reports. Results are discussed in terms of the Dow‐Redfield model of exponential absorption edges, t...
170 citations
TL;DR: For economical and efficient utilization of solar energy various types of absorber coatings and preparations can be used for solar collectors as discussed by the authors, and several varieties of commercial and research selective absorbers are reviewed and tabulated for application.
163 citations
TL;DR: In this paper, a spectral feature, apparently an absorption line, has been observed at an energy of 20.1 + or - 0.5 keV in the pulsed flux of the 3.61-s X-ray pulsar 4U 0115+63 by using the UCSD/MIT instrument on HEAO 1.
Abstract: A spectral feature, apparently an absorption line, has been observed at an energy of 20.1 + or - 0.5 keV in the pulsed flux of the 3.61-s X-ray pulsar 4U 0115+63 by using the UCSD/MIT instrument on HEAO 1. The line strength, expressed as equivalent width, is 3.1 + or - 0.5 keV. Although essentially unresolved, the feature has a depth more than 60% of the continuum flux. If the feature arises by cyclotron resonance absorption near the magnetic poles of the neutron star, it implies a magnetic field of between approximately 1.8 and 2.5 x 10 to the 12th G, depending on the gravitational redshift (no more than about 5-40%).
TL;DR: The optical constants of amorphous thin films of Sb2S3 prepared by vacuum evaporation were determined by means of transmission electron microscopy as discussed by the authors, and the optical constants in the amorphized films are rather structureless but on crystallization several structures are observed in e2 at energies of 1.88, 2.48, 3.86 and 5.25 eV.
TL;DR: Three approximately isonitrogenous diets were used and marked increases in flow of N, LN and NPLN were seen in the duodenum and jejunum after feeding each diet, but not in the ileum, in which widely different observations were made.
Abstract: 1. Digesta were collected from twenty-three pigs, initially of 30 kg live weight, and fitted with single Ash re-entrant cannulas in either the duodenum, jejunum or ileum. A further twenty-four pigs were used in a conventional digestibility trial. 2. Three approximately isonitrogenous diets were used; they contained: barley, fine wheat offal, white fish meal, minerals and vitamins (diet BWF), starch, sucrose, maize oil, cellulose, minerals, vitamins and either groundnut (diet SSG) or casein (diet SSC). 3. The flow-rates of nitrogen (N), liquid-fraction N (LN) and non-protein liquid-fraction N (NPLN) were measured hourly in the duodenum and jejunum and every 6 h in the ileum during 24 h collection periods. Faeces were collected during 5 d periods. 4. Marked increases in flow of N, LN and NPLN were seen in the duodenum and jejunum after feeding each diet, but not in the ileum. 5. Values for, N output: intake from the duodenal, jejunal or ideal cannulas and in faeces in 24 h periods were respectively: 0.98, 0.88, 0.25 and 0.21 for diet BWF; 1.00, 0.97, 0.22 and 0.24 for diet SSG; 0.98, 0.73, 0.09 and 0.03 for diet SSC. The corresponding values for LN in the duodenum, jejunum and ileum respectively were: 0.53, 0.53 and 0.12 for diet BWF; 0.46, 0.60 and 0.13 for diet SSG; 0.57, 0.50 and 0.06 for diet SSC. The corresponding values for NPLN in the duodenum, jejunum and ileum respectively were: 0.41, 0.38 and 0.09 for diet BWF; 0.35, 0.36 and 0.08 for diet SSG; 0.46, 0.38 and 0.04 for diet SSC. 6. The results are discussed in relation to similar studies, particularly in pigs with duodenal cannulas, in which widely different observations were made.
TL;DR: For a given concentration and optical depth, the absorption was found to be dependent on the imaginary part, n2, of the complex index of refraction, n = n 1 − in 2, of material used.
TL;DR: Calculations indicate that the maximum daily solar radiation reaching the Martian surface is about 325 cal/cm2 during southern hemisphere summer at latitude of about 40°S, which is within 10% of the radiation incident on the atmosphere.
Abstract: Calculations indicate that the maximum daily solar radiation reaching the Martian surface is about 325 cal/cm2 during southern hemisphere summer at latitude of about 40°S. In the ultraviolet region of the spectrum, the radiation reaching the surface at wavelengths greater than 2800 A is within 10% of the radiation incident on the atmosphere. There is significant extinction of radiation in the spectral region near 2500 A in mid and high latitudes due to absorption of radiation by ozone; radiation reaching the surface may be reduced to one one-thousandth of that incident on the atmosphere during winter. Virtually no radiation of wavelengths less than 1900 A reaches the surface because of absorption by the large column abundance of carbon dioxide. Daily and latitudinal distributions of radiation are presented for wavelengths of 3000, 2500 and 2000 A.
TL;DR: In this paper, the absorption near the fundamental absorption edge of Hg1−xCdxTe was measured over the composition range 0.205 ⩽x⩽0.220 at temperatures from 80 to 300 K.
Abstract: The absorption near the fundamental absorption edge of Hg1−xCdxTe was measured over the composition range 0.205⩽x⩽0.220 at temperatures from 80 to 300 K. The dispersion of the index of refraction of Hg1−xCdxTe was obtained from the interference pattern. It was found that the absorption tail obeys a modified Urbach’s rule and is expressed by α=α0 exp[σ (E−E0)/(T+T0)] for 20⩽α (cm−1) ⩽1000. The fitting parameters α0, σ, T0, and E0 vary regularly with x. The expression is used to obtain the absorption coefficient and the temperature coefficient of the gap as a function of x and T. Evidence is presented to show that these parameters may be extrapolated to calculate the absorption beyond the measured composition range.
01 Nov 1979
TL;DR: In this article, the extinction cross section for an arbitrary spherical particle that is embedded in an absorbing medium is derived by considering that which is measured in an actual extinction experiment, and the resultant "optical theorem" is similar in form to the optical theorem for particles in a nonabsorbing medium.
Abstract: The extinction cross section for an arbitrary spherical particle that is embedded in an absorbing medium is derived by considering that which is measured in an actual extinction experiment. The resultant “optical theorem” is similar in form to the optical theorem for particles in a nonabsorbing medium. Calculations of extinction by germanium particles that are embedded in a polyethylene medium at room temperature have been performed for far-infrared frequencies (50–200 cm−1). If the imaginary part of the medium refractive index is ignored, then particulate extinction is underestimated by factors of between 2 and 4 over the frequency range of interest for 0.02-μm-radius spheres. In addition, there is a significant shift of a bulk germanium absorption maximum, which is not predicted when the medium is assumed to be nonabsorbing. For larger particles, the relative error decreases but still may be significant.
TL;DR: In this article, the x-ray emission of gold disks has been irradiated with 1.06 μm laser light at intensities between 7 × 1013 and 3 × 1015 W/cm2, and pulse lengths between 200 and 1000 psec.
Abstract: Gold disks have been irradiated with 1.06 μm laser light at intensities between 7 × 1013 and 3 × 1015 W/cm2, and pulse lengths between 200 and 1000 psec. Due to the high Z and long pulse, inverse bremsstrahlung becomes an important absorption mechanism and competes strongly with resonance absorption and stimulated scattering. In addition to measured absorptions, data on the temporal, spatial, angular, and spectral characteristics of the x‐ray emission are presented. Temporally and spectrally resolved back‐reflected light, and polarization‐dependent sidescattered light are detected, providing estimates for the amount of stimulated scattering and of the coronal electron temperature. Inhibited electron thermal conduction and nonlocal thermodynamic equilibrium ionization physics play key roles in bringing numerical simulations of these experiments into agreement with all of the above‐mentioned data.
TL;DR: In this paper, a general theory of optical bistability for a homogeneously broadened two-level system in a Fabry-Perot interferometer is presented.
Abstract: A general theory of optical bistability for a homogeneously broadened two-level system in a Fabry-Perot interferometer is presented. Both absorptive and dispersive mechanisms are included, and in the mean-field approximation a cubic state equation is derived relating transmitted intensity to all physical parameters. From the perspective of catastrophe theory, this equation describes an elementary cusp catastrophe. We show that bistable switching may follow not only from sweeping the incident laser intensity, but also with continuous variation of atomic or cavity detuning, or atomic density, with the laser intensity fixed. For the case having incident intensity as the variable control, the domain of bistability is studied in some detail as a function of the remaining fixed parameters. Stability criteria are considered for the general case including both absorption and dispersion.
TL;DR: In this article, a simple three-band model calculation provides a single comprehensive description of both the magnitude and the frequency dependence of the two-photon absorption coefficient for a wide range of III-V and II-VI zinc-blende semiconductors.
Abstract: Two-photon absorption can become the dominant loss mechanism for semiconductors subjected to sufficiently intense laser light in the frequency range Svp&E, &28p, where +p is the laser frequency and E, is the energy gap. The proper understanding of this effect can yield information not accessible to one-photon transitions, and is important for the operation of a number of devices such as \"inducible absorbers, \" twophoton-pumped and spin-flip Raman lasers, and infrared detectors. There has been a long-standing discrepancy, in some cases of more than an order of magnitude, between reports of the measured frequency dependence of the two-photon absorption coefficient and the theoretically predicted values, in particular for two-photon energies much greater than E, (see, for example, Basov et al. ,' Lee and Fan, ' and Doviak et al. ') We show in the present work that a simple three-band model calculation provides a single comprehensive description of both the magnitude and the frequency dependence of the two-photon absorption coefficient for a wide range of III-V and II-VI zinc-blende semiconductors. For a given photon energy the magnitude of the coefficient d(An) Kal dt 28&p (2)
TL;DR: The Pioneer Venus Orbiter ultraviolet spectrometer has seen variable disk brightness features similar to the well-known "UV markings" seen at longer wavelengths as discussed by the authors, which are consistent with a homogeneous cloud of H2SO4 aerosols.
Abstract: The Pioneer Venus Orbiter ultraviolet spectrometer sees variable disk brightness features similar to the well-known 'UV markings' seen at longer wavelengths. The bright features are consistent with a homogeneous cloud of H2SO4 aerosols. The darker features show the presence of a broad-band absorber, which is at some depth in the cloud layer. Additional contrast arises from SO2 absorption. The observed strength of the SO2 absorption as a function of wavelength rules out a uniform mixing ratio for the SO2. The data are well fitted by an inhomogeneous light scattering model in which the SO2 scale height is one-fifth of the CO2 scale height, and the mixing ratio of SO2 at 40 mb is 10 to the -7th. A model of the oxidation of sulfur dioxide in the upper cloud reproduces the observed vertical distribution of SO2 and indicates that SO2 alone is sufficient to produce the observed amount of H2SO4 in this region.
TL;DR: In this article, the distribution of absorption centers within an absorbing sphere under monochromatic, parallel illumination is presented for the equatorial plane, where the main features of the topography become increasingly structured with increasing magnitude of the size parameter and the real part of the refractive index.
Abstract: This paper presents the distribution of absorption centers within an absorbing sphere under monochromatic, parallel illumination. Results for the equatorial plane are represented by topographical perspective views for size parameters a, up to 5, and for refractive indices up to m = 3.0−0.1i. The main features of the topography become increasingly structured with increasing magnitude of the size parameter and the real part of the refractive index. Although the imaginary part of the refractive index strongly influences the magnitude of the absorption, it does not influence the shape of the topography as long as the imaginary part is less than the real part of the refractive index. Results are also presented for m = 1.95−0.66i corresponding to carbon. The source function, which is depicted for the first time in this paper, must be the starting point for any theory of radiation pressure on small absorbing particles, for photophoresis, or for other phenomena concerned with the temperature distribution within irradiated particles.
TL;DR: In this paper, the spectrum of the highly obscured infrared source W33 A from 4.5 to 8 microns is measured in order to investigate the intervening cold, dense interstellar material, and the absorption at 4.61, 5.99 and 6.78 microns are interpreted as evidence of absorption in the resonance bands of carbonyl, carbon-carbon double, methyl and methylene bonds of hydrocarbons associated with interstellar dust.
Abstract: The spectrum of the highly obscured infrared source W33 A from 4.5 to 8 microns is measured in order to investigate the intervening cold, dense interstellar material. Spectrophotometry at a relative spectral resolution of about 0.015 by an airborne filter-wheel infrared spectrometer reveals strong absorption features at 4.61, 5.99 and 6.78 microns. The absorption at 4.61 microns is attributed primarily to the fundamental vibration-rotation band of CO at a column density (at least 10 to the 19th/sq cm) which is 10% of the carbon inferred from silicate abundances. The strengths and line widths of the absorption agt 5.99 and 6.78 microns are interpreted as evidence of absorption in the resonance bands of carbonyl, carbon-carbon double, methyl and methylene bonds of hydrocarbons associated with interstellar dust.
TL;DR: An inverse relationship was found between particle size and lead absorption; this relationship was most marked in the 0 to 100 micron range.
Abstract: The relationship between particle size and absorption of lead particles from the gastrointestinal tract of the rat has been investigated. Preparations of metallic lead of particle size between 0 and 250μ were incorporated in laboratory rat diets and absorption determined by measurement of tissue lead concentrations attained under standard conditions. An inverse relationship was found between particle size and lead absorption; this relationship was most marked in the 0 to 1001μ range. A five-fold enhancement of absorption was observed from the diet with lead particles of mean size 6μ, compared with 197μ particle size. Lead absorption from dried paint films containing lead chromate and lead octoate was measured using a similar technique. A marked enhancement of absorption was observed for both paints when particle size was reduced from 500 to 1,000 μ to < 50μ.
TL;DR: In this paper, a statistical technique is developed for inferring the optimum values of the ground albedo and the effective imaginary term of the complex refractive index of atmospheric particulates.
Abstract: A statistical technique is developed for inferring the optimum values of the ground albedo and the effective imaginary term of the complex refractive index of atmospheric particulates. The procedure compares measurements of the ratio of the hemispheric diffuse to directly transmitted solar flux density at the earth’s surface with radiative transfer computations of the same as suggested by Herman el al. (1975). A detailed study is presented which shows the extent to which the ratio of diffuse to direct solar radiation is sensitive to many of the radiative transfer parameters. Results indicate that the optical depth and size distribution of atmospheric aerosol particles are the two parameters which uniquely specify the radiation field to the point where ground albedo and index of absorption can be inferred. Varying the real part of the complex refractive index of atmospheric particulates as well as their vertical distribution is found to have a negligible effect on the diffuse-direct ratio. The statistical procedure utilizes a semi-analytic gradient search method from least-squares theory and includes a detailed error analysis.
TL;DR: In this article, a CO 2 laser with incident flux up to about 20 W/cm 2 under autoignition and piloted ignition in air was used for radiative ignition experiments on PMMA and red oak.
TL;DR: In this article, the authors identify the broad absorption feature below 3300 A in the Venus UV spectrum is primarily due to SO2 absorption based on new higher resolution spectra of the 3000-3400 A region showing broad (10 A), unresolved absorptions in the regions at all SO2 band origins between 3000 and 3300A.
Abstract: The broad absorption feature below 3300 A in the Venus UV spectrum is identified as primarily due to SO2 absorption based on new higher resolution spectra of the 3000-3400 A region showing broad (10 A), unresolved absorptions in the regions at all SO2 band origins between 3000 and 3300 A. SO2 mixing ratios vary from 5 x 10 to the -7th down to an upper limit of 2 x 10 to the -8th at a phase angle of 138 deg. Previous observational determinations of the SO2 mixing ratio were biased toward large phase angles, and consequently did not detect any SO2 absorption at the 10 to the -8th level. The upper limit derived from the CS2 band head at 3206 A is not greater than 5 x 10 to the -8th. The observed range of SO2 mixing ratios is consistent with model predictions based on the sulfur photochemistry at the cloud tops. Ground-based observations of SO2 mixing ratio will provide constraints on models and check on the Venera and Pioneer Venus measurements of the mixing ratios of SO2 and other sulfur-bearing gases with altitude.
TL;DR: In this article, a pulsed-dye-laser optoacoustic spectroscopy technique was used to measure the weak visible absorption band of benzene near 607 nm, due to the sixth harmonic of the C-H stretch.
Abstract: We report a pulsed‐dye‐laser optoacoustic spectroscopy technique for sensitive measurements of weak absorption spectra of liquids. We have used this technique to measure the weak visible absorption band of benzene near 607 nm, due to the sixth harmonic of the C‐H stretch. We obtain a signal‐to‐noise ratio exceeding 102 at the absorption peak. We estimate that with improved data handling, absorption features as small as 10−7 cm−1 should be detectable in liquids. This opens up new possibilities of trace‐constituent detection and pollution monitoring in the liquid phase.