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Showing papers on "Absorption (electromagnetic radiation) published in 1993"


Journal ArticleDOI
TL;DR: In this paper, the authors used a variety of refractive indices to measure the light absorption coefficient of suspended particles in the atmosphere and found that the mass extinction coefficient of soot is higher by a factor of two to three compared to transparent particles.

554 citations


Journal ArticleDOI
TL;DR: In this paper, a multiple scattering correction was calculated from optical density spectral for 48 phytoplankton cultures of seven species representing a variety of cell sizes, pigment groups, and call-wall types.
Abstract: : Absorption spectra measured for aquatic particles concentrated onto glass-fiber filters require a correction for the increase in pathlength caused by multiple scattering in the glass-fiber filter. A multiple scattering correction was calculated from optical density spectral for 48 phytoplankton cultures of seven species representing a variety of cell sizes, pigment groups, and call-wall types. The relationship between optical density in suspensions and on filters was not wavelength-dependent. Differences between blank filters were always spectrally neutral. Small differences between relationships for single species were inconclusive. Given the absence of wavelength-dependent effects, we report a single general quadratic relationship, OD(susp)(lambda) = 0.378 OD(filt)(lambda) + 0.523 OD(filt)(lambda)2 (r2 = 0.988), for correcting glass- fiber filter spectra. For independent samples, the average error in predicting OD(susp)(lambda) with this algorithm at any wavelength was 2%. Greatest errors were in spectral regions of low absorption. Absorption spectra for particles concentrated onto glass-fiber filters can be quantitatively corrected for multiple scattering within this limit. Applicability of the algorithm to field samples of varied composition was enhanced by using a large number of spectra and a range of cell types in algorithm development. Optical oceanography, Physical oceanography, Absorption, Scattering.

375 citations



Journal ArticleDOI
TL;DR: In systems that are two and three dimensional electronically, a large polaron and a small polaron are distinct types of quasiparticles, which depends on which electron-lattice interaction is of primary importance.
Abstract: In systems that are two and three dimensional electronically, a large polaron and a small polaron are distinct types of quasiparticles. The type of polaron formed depends on which electron-lattice interaction is of primary importance. A large polaron forms when the electron-lattice interaction due to the long-range Coulombic interactions between an electronic carrier and a solid's ions are of paramount importance. Competing effects then determine the radius of a large polaron. By contrast, a small polaron can form when a short-range electron-lattice interaction, such as the deformation-potential interaction, is dominant. A small polaron forms as its self-trapped carrier shrinks without limit until it is confined to a single site. Fundamental differences between large and small polarons produce optical spectra with distinguishing features. The absorption due to photoionization of a large polaron depends on products of the matrix elements for exciting a carrier from its self-trapped states to a free-carrier state and the density of these free-carrier states. These matrix elements fall sharply with increasing free-carrier wave vector k when kRg1, where R is the large polaron's radius. A large polaron's photoionization produces a temperature-independent absorption band. This band is asymmetric with the absorption intensity on the high-energy side of the peak exceeding that on the low-energy side of the peak.By contrast, the small-polaron absorption arises as the self-trapped carrier is induced to transfer from its well-localized state to a localized state at an adjacent site. Phonon broadening of these local electronic energy levels produces the widths of these absorption bands. Small-polaron absorption bands are asymmetric with the absorption intensity below the peak energy exceeding that above the peak energy. With rising temperature the phonon broadening of the local electronic energy levels progressively broadens these absorption bands. In addition, the motion of a polaron in response to an ac field can produce a (Drude-like) free-carrier absorption. A large polaron's free-carrier absorption occurs at frequencies below the characteristic phonon frequency. By contrast, if the narrow bands that characterize small polarons did not result in their localization, their coherent motion would produce a free-carrier absorption that is restricted to frequencies far below the phonon frequency. The optical spectra of large and small bipolarons are similar to those for large and small polarons, respectively. Finally, carrier-induced absorption bands observed in semiconducting and superconducting cuprates are compared with the expectations of large- and small-polaronic absorptions. The high-frequency absorption bands are consistent with the existence of large-polaronic carriers. However, taken together, the free-carrier absorptions and the dc transport in the superconductors depart from expectations of independent polaronic carriers. It is suggested that if the carriers in the cuprates are polaronic, their transport in the superconductors' normal states is collective.

335 citations


Journal ArticleDOI
TL;DR: A new material containing macroscopic quantities of hollow nanometric carbon onions with from 2 to about 8 graphitic shells, with outer diameters ranging from 3 to 10 nm (characterized by high-resolution electron microscopy), is produced by heat treatment of pure carbon soot.

287 citations


Journal ArticleDOI
TL;DR: The initial optical zone may be altered by the formation of char during high-irradiance laser exposure, and a spectrum of char absorbance is presented.
Abstract: The primary zone of deposition of optical energy is called here the optical zone. The tissue absorption, tissue scattering, laser-beam diameter, or size of pigmented structures can specify the size of the optical zone. The initial optical zone may be altered by the formation of char during high-irradiance laser exposure, and a spectrum of char absorbance is presented. The relationship between the optical zone and the pulse duration specifies the type of laser-tissue interaction that may occur. Short laser pulses can confine thermal energy and/or stress energy within the optical zone, which maximizes photothermal and photomechanical mechanisms of interaction.

264 citations


Book
01 May 1993

258 citations


Journal ArticleDOI
01 Dec 1993-Polymer
TL;DR: A filled epoxy resin used as a structural adhesive and based on the diglycidyl ether of bisphenol A cured with dicyandiamide has been subjected, in its bulk form, to ageing at 40, 55 and 70°C and ca. 100% relative humidity as discussed by the authors.

255 citations


Journal ArticleDOI
TL;DR: A tunable diode laser diagnostic based on spectrally resolved laser absorption has been developed to detect water vapor and accurately determined required data for H(2)O line strengths and self-broadening coefficients for several spectral lines in a static cell filled with pure water vapor.
Abstract: A tunable diode laser diagnostic based on spectrally resolved laser absorption has been developed to detect water vapor. The system uses a distributed feedback InGaAsP diode laser, emitting at ~ 1.38 µm. The diode laser is tuned in wavelength by modulation of the current, resulting in 1-cm(-1) tuning at 80-Hz repetition rate. The directly measured absorption spectra yield values for water-vapor concentration and temperature, as well as a collision-broadening line shape. To our knowledge, we accurately determined required data for H(2)O line strengths and self-broadening coefficients for several spectral lines in a static cell filled with pure water vapor. The temperature and concentration of the water vapor present in laboratory room air and in the postflame gases above a methane-air flat flame burner have also been measured. These results agree well with calculated values and independent measurements.

250 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a semi-empirical method to determine the optimum aperture size and operating temperature of a solar cavity-receiver for which its energy conversion efficiency is maximized.

242 citations


Journal ArticleDOI
TL;DR: In this paper, the photophysical properties of poly(p-phenylene vinylene), PPV, prepared in a way that gives an especially high degree of intrachain order are investigated.
Abstract: The authors report a study of the photophysical properties of poly(p-phenylene vinylene), PPV, prepared in a way that gives an especially high degree of intrachain order. Optical absorption, photoluminescence, photoinduced absorption, and photoconductivity excitation spectra are presented and compared to data reported for less well ordered PPV. Spectral red shifts, sharpening of spectral lines, and a transfer of oscillator strength into the vibronic ground states of the electronic transitions are observed. Photoinduced absorption due to long-lived charged excitations, previously reported for less ordered PPV, could not be detected in this material. Photoconductivity excitation spectra show a steep rise at the absorption edge with no appreciable offset between the onsets for photoconduction and absorption. A very slow photocurrent component is observed, which the authors associated with the trapping and subsequent thermal release of photocarriers.

Journal ArticleDOI
TL;DR: In this paper, two seismic wave attenuation factors, scattering attenuation (Qs−1) and intrinsic absorption (Qi−1), can be determined from estimates of two parameters, the reciprocal of extinction length Le−1 ≡ (Q s−1 + Qi − 1) ·ω/v and seismic albedo B0≡ Qs− 1 / (Q S − 1 + Qi− 1), where ω and v are angular frequency and seismic wave velocity.
Abstract: Two seismic wave attenuation factors, scattering attenuation (Qs−1) and intrinsic absorption (Qi−1), can be determined from estimates of two parameters, the reciprocal of extinction length Le−1 ≡ (Qs−1 + Qi−1) ·ω/v and seismic albedo B0≡ Qs−1 / (Qs−1 + Qi−1), where ω and v are angular frequency and seismic wave velocity, respectively. These parameters are measured using the multiple lapse time window analysis method over frequency bands of 1–2, 2–4, and 4–8 Hz from 16 stations located throughout Japan. In the analysis, time-integrated seismic wave energy from earthquakes having hypocentral distances less than 120 km and focal depths less than 40 km are compared with simulations of multiple isotropic scattering based on the assumption of spatial uniformity of Qs−1 and Qi−1. The modified coda normalization method is used to correct for sources and site effects, where the spatially non uniform distribution of the coda wave energy is considered. The Le−1 estimates do not have a distinct frequency dependence, but the Be estimates do: 0.2–0.7 for 1–2 Hz and 0.1–0.3 for 4–8 Hz. The results mean that Qs−1 is similar to Qi−1 for 1–2 Hz but is 3–5 times smaller for 4–8 Hz and that the frequency dependence of Qs−1 is larger than Qi−1. Analyses using different components of motion and different window lengths give nearly the same results. Coda attenuation (Qc−1) estimates based on the single scattering approximation are nearly equal to intrinsic absorption Qi−1 rather than to total attenuation (Qs−1 + Qi−1) for Japan.

Journal ArticleDOI
TL;DR: In this article, the absorption line properties of six Mg II broad absorption line quasars (BALQs) are examined using a BALQ sample of Weymann et al.
Abstract: The absorption line properties of six Mg II broad absorption line quasars (BALQs) are examined using a BALQ sample of Weymann et al. (1991). It is found that Al III absorption is always stronger than Al II absorption; C IV absorption tends to be very deep and broad; and low ionization absorption tends to be narrower and lie at the low velocity end of the C IV trough. The results indicate that the outflows in Mg II BALQs are not accelerating monotonically. It is shown that a hot cloud-confining outflow can be decelerated by adding thick absorbing clouds provided the ionization parameters of these clouds are high. It is argued that the MG II BALQ phenomenon might be a manifestation of a quasar's efforts to expel a thick shroud of gas and dust.

Journal ArticleDOI
TL;DR: In this paper, the optical properties of red perylimide laser dye in various solvents were studied, including cyclohexane, methanol and xylenes.

Journal ArticleDOI
TL;DR: Extensive transient absorbance data are fully consistent with a stepwise electron transfer via the accessory bacteriochlorophyll and an angle between the transition moments of the special pair and the species related with the 0.9-ps kinetic component is found.
Abstract: The primary electron transfer in reaction centers of Rhodobacter sphaeroides is studied by subpicosecond absorption spectroscopy with polarized light in the spectral range of 920-1040 nm. Here the bacteriochlorophyll anion radical has an absorption band while the other pigments of the reaction center have vanishing ground-state absorption. The transient absorption data exhibit a pronounced 0.9-ps kinetic component which shows a strong dichroism. Evaluation of the data yields an angle between the transition moments of the special pair and the species related with the 0.9-ps kinetic component of 26 +/- 8 degrees. This angle compares favorably with the value of 29 degrees expected for the reduced accessory bacteriochlorophyll. Extensive transient absorbance data are fully consistent with a stepwise electron transfer via the accessory bacteriochlorophyll.

Journal ArticleDOI
TL;DR: The quantitative relationship between the absorption and fluorescence emission of chromophoric (colored) dissolved organic matter (CDOM) has been determined along five cruise tracks in the western North Atlantic Ocean, the Gulf of Mexico, and Monterey Bay, and includes Gulf Stream, Loop Current, slope, shelf and coastal waters as mentioned in this paper.
Abstract: The quantitative relationship between the absorption and fluorescence emission of chromophoric (colored) dissolved organic matter (CDOM) has been determined along five cruise tracks in the western North Atlantic Ocean, the Gulf of Mexico, and Monterey Bay, and includes Gulf Stream, Loop Current, slope, shelf, and coastal waters. We present a protocol for the determination of CDOM fluorescence that will allow both interlaboratory comparisons and the calibration of airborne fluorescence measurements. This protocol is based on the use of the water Raman signal as an internal radiometric standard and quinine sulfate as an external standard. This study demonstrates that when an appropriate and consistent procedure is used to standardize fluorescence measurements, the fluorescence per unit absorption exhibits surprisingly little variation for diverse waters. The maximum variability observed between all sites was 36% and within the western North Atlantic the variability was only 12%. Algorithms are presented for retrieval of the absorption coefficient of CDOM at 355 and 337 nm from shipboard or airborne measurements of the water-Raman-normalized fluorescence emission resulting from 355- and 337-nm excitation.

Journal ArticleDOI
TL;DR: In this article, an accurate line-by-line model is used to evaluate effects of absorption in the Schumann-Runge bands of O2 on transmission of UV radiation, and it is shown that photochemical loss of odd oxygen exceeds production by photolysis of O 2 for altitudes above 40 km.
Abstract: An accurate line-by-line model is used to evaluate effects of absorption in the Schumann-Runge bands of O2 on transmission of UV radiation. The model is used to evaluate rates of photolysis for N2O, CFCl3, and CF2Cl2, and to infer global loss rates and instantaneous lifetimes appropriate for 1980. A parameterized version of the line-by-line model enabling rapid evaluation of transmission in the Schumann-Runge region is described. Photochemical calculations employing the parameterization and constrained by data from the Atmospheric Trace Molecule Spectroscopy experiment are used to examine the budget of odd oxygen. Consistent with previous studies, it is shown that photochemical loss of odd oxygen exceeds production by photolysis of O2 for altitudes above 40 km. The imbalance between production and loss is shown to be consistent with a source of odd oxygen proportional to the product of the mixing ratio and photolysis rate of ozone, which suggests that processes involving vibrationally excited O2 may play an important role in production of odd oxygen.

Journal ArticleDOI
TL;DR: In this article, the absorption cross sections σO3 in the temperature range 200-300 K were used to estimate the atmospheric transmission and photolysis frequencies. But the experimental results were limited to the case of O3 and O3 is one of the most important minor components of the troposphere and stratosphere.

Journal ArticleDOI
TL;DR: In this paper, the contributions of detrital particles and phytoplankton to total light absorption are retrieved by nonlinear regression on the absorption spectra of total particles from various oceanic regions.
Abstract: The contributions of detrital particles and phytoplankton to total light absorption are retrieved by nonlinear regression on the absorption spectra of total particles from various oceanic regions. The model used explains more than 96% of the variance in the observed particle absorption spectra. The resulting absorption spectra of phytoplankton are then decomposed into several Gaussian bands reflecting absorption by phytoplankton pigments. Such a decomposition, combined with high-performance liquid chromatography data on phytoplankton pigment concentrations, allows the computation of specific absorption coefficients for chlorophylls a, b, and c and carotenoids. The spectral values of these in vivo absorption coefficients are then discussed, considering the effects of secondary pigments which were not measured quantitatively. We show that these coefficients can be used to reconstruct the absorption spectra of phytoplankton at various locations and depths. Discrepancies that do occur at some stations are explained in terms of particle size effect. These coefficients can be used to determine the concentrations of phytoplankton pigments in the water, given the absorption spectrum of total particles.


Journal ArticleDOI
TL;DR: The theory of G6rardy and Ausloos was applied to compute the total extinction loss spectra of several aggregates of nanometer-sized silver spheres from the near IR to the near UV to give general results that are independent of the particle material.
Abstract: Light scattering and absorption by spherical particles is extended to aggregates of spheres with arbitrary shape and size. We applied the theory of Gerardy and Ausloos [Phys. Rev. B 25, 4204–4229 (1082)] to compute the total extinction loss spectra of several aggregates of nanometer-sized silver spheres from the near IR to the near UV. Silver was best suited to provide quantitative comparison with experiments concerning the scattering and absorption in the visible spectral region. Additional resonant extinction was obtained besides the resonant extinction of the single silver sphere. The spectra were discussed in detail to give general results that are independent of the particle material.

Journal ArticleDOI
TL;DR: In this article, the first direct pump-probe transient absorption measurements on the near-infrared (IR) band of the equilibrated aqueous solvated electron were performed.
Abstract: We have performed the first direct pump‐probe transient‐absorption measurements on the near‐infrared (IR) band of the equilibrated aqueous solvated electron. The pump pulse was centered at 780 nm. The absorption spectrum of the excited state is observed to be red‐shifted relative to the ground‐state absorption. The radiationless transition from the excited state to the ground state occurs with an average time constant of 550±170 fs. In observing a subpicosecond lifetime and red‐shifted absorption for the excited p‐states, these experiments are in accord with a growing body of experimental and theoretical work, serving to provide a consistent picture of the photophysics of the solvated electron.

Journal ArticleDOI
TL;DR: In this paper, the temperature dependences of the spectral and total hemispherical emissivities of silicon have been experimentally determined, by using a technique which combines isothermal electron beam heating with in situ optical measurements.
Abstract: The temperature dependences of the spectral and total hemispherical emissivities of silicon have been experimentally determined, by using a technique which combines isothermal electron beam heating with in situ optical measurements. Emission spectra were used to deduce the absorption coefficient for phosphorus‐doped silicon samples for wavelengths between 1.1 and 1.6 μm, in the temperature range from 330 to 800 °C. For lightly doped samples, the data show good agreement with a model which includes the effects of the various phonon‐assisted processes involved in interband transitions in silicon, as well as the free‐carrier absorption. For heavily doped samples the agreement was less satisfactory, possibly because of inadequacies in the model for free‐carrier absorption. It was shown that reflection spectra can also be used to determine the absorption spectrum, for the range where the absorption coefficient lies between 1 and ∼70 cm−1. By fitting the theoretical model to the absorption coefficients derived ...

Journal ArticleDOI
TL;DR: In this paper, Kramers-Kronig transformation was performed on the reflectance data to obtain the optical and dielectric properties of glasses over a broad and continuous spectral range (30-4000 cm−1).
Abstract: Alkali diborate glasses have been investigated by infrared reflectance spectroscopy to demonstrate the potential of this technique for a quantitative description of the glass structure. Kramers-Kronig transformation was performed on the reflectance data to obtain the optical and dielectric properties of glasses over a broad and continuous spectral range (30–4000 cm−1). Analysis of the mind infrared spectra shows that the normalized absorption area attributed to boron-oxygen tetrahedra decreases upon increasing alkali cation ionic radius, and scales linearly with the fraction of four-coordinated boron atoms determined recently from NMR spectra. The far infrared asymmetric absorption profiles were deconvoluted into two broad bands and attributed to vibrations of alkali cations in two distinct network environments. Cation effective charges were calculated from the integrated absorption of the bands due to cation vibrations, and were found to increase with alkali ionic radius.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate a new technique for enhancing the absorption of high-intensity, ultrashort-duration laser pulses by solids, such as gold gratings and gold clusters.
Abstract: We demonstrate a new technique for enhancing the absorption of high‐intensity, ultrashort‐duration laser pulses by solids. Targets consisting of gold gratings and gold clusters were found to absorb greater than 90% of the incident high‐intensity laser light. This is in contrast to less than 10% absorption by flat surfaces. As a result of this strong coupling of the laser to a high‐density plasma, conversion efficiency of laser energy to x rays of greater than 1% was observed for x rays above 1 keV. Efficiency of nearly 25% was observed for emissions greater than 30 eV. These conversion efficiencies are more than an order of magnitude greater than those measured from flat targets.

Journal ArticleDOI
TL;DR: In this paper, sub-gap absorption was measured under forward drive conditions in electroluminescent devices fabricated from thin films of poly( p -phenylenevinylene) sandwiched between electrodes of indium/tin oxide and calcium.

Journal ArticleDOI
TL;DR: In this paper, the optical and electronic properties of highly tetrahedral amorphous diamond-like carbon (amorphous diamond, a-D) films were investigated using electron energy loss spectroscopy.

Journal ArticleDOI
TL;DR: It is shown that the kinetics of the energy transfer from a long-wavelength antenna pigment to a hypsochromically absorbing primary donor does not represent a major kinetic limitation and means an evolutionary advantage based on the chromatic adaptation of photosynthetic organelles to spectrally filtered light caused by self-absorption.
Abstract: The light-harvesting apparatus of photosynthetic organisms is highly optimized with respect to efficient collection of excitation energy from photons of different wavelengths and with respect to a high quantum yield of the primary photochemistry. In many cases the primary donor is not an energetic trap as it absorbs hypsochromically compared to the most red-shifted antenna pigment present (long-wavelength antenna). The possible reasons for this as well as for the spectral heterogeneity which is generally found in antenna systems is examined on a theoretical basis using the approach of thermal equilibration of the excitation energy. The calculations show that long-wavelength antenna pigments and heterogeneous absorption bands lead to a concentration of excitons and an increased effective absorption cross section. The theoretically predicted trapping times agree remarkably well with experimental data from several organisms. It is shown that the kinetics of the energy transfer from a long-wavelength antenna pigment to a hypsochromically absorbing primary donor does not represent a major kinetic limitation. The development of long-wavelength antenna and spectrally heterogeneous absorption bands means an evolutionary advantage based on the chromatic adaptation of photosynthetic organelles to spectrally filtered light caused by self-absorption.

Journal ArticleDOI
TL;DR: The result shows that absorption of infrared light of moderate intensity can lead to photoionization in rare-earth-doped glass, provided that a multiphoton stepwise excitation channel exists.
Abstract: Permanent photoinduced optical attenuation has been observed in Tm(3+)-doped aluminosilicate glass fibers on exposure to near-resonance mode-locked 1064-nm radiation at 300 K. The rate of this darkening was observed to follow a 4.7 +/- 0.4 power dependence on the 1064-nm intensity. The result shows that absorption of infrared light of moderate intensity can lead to photoionization in rare-earth-doped glass, provided that a multiphoton stepwise excitation channel exists.

Journal ArticleDOI
TL;DR: In this article, the optical properties and water absorption properties of thin oxide films were studied and it was shown that the films are porous and have a packing density lower than that of the corresponding bulk material.