Showing papers on "Absorption (electromagnetic radiation) published in 1989"
TL;DR: In this article, a modular assembly approach is proposed to integrate light absorption, energy transfer, and long-range electron transfer by use of free-energy gradients into single molecular assemblies or on separate electrodes in photelectrochemical cells.
Abstract: The goal of artificial photosynthesis is to use the energy of the sun to make high-energy chemicals for energy production. One approach, described here, is to use light absorption and excited-state electron transfer to create oxidative and reductive equivalents for driving relevant fuel-forming half-reactions such as the oxidation of water to O2 and its reduction to H2. In this “integrated modular assembly” approach, separate components for light absorption, energy transfer, and long-range electron transfer by use of free-energy gradients are integrated with oxidative and reductive catalysts into single molecular assemblies or on separate electrodes in photelectrochemical cells. Derivatized porphyrins and metalloporphyrins and metal polypyridyl complexes have been most commonly used in these assemblies, with the latter the focus of the current account. The underlying physical principleslight absorption, energy transfer, radiative and nonradiative excited-state decay, electron transfer, proton-coupled elec...
1,260 citations
IBM1
TL;DR: By analyzing the propagation of terahertz electromagnetic pulses through water vapor, this work has made what it is believed are the most accurate measurements to date of the absorption cross sections of the water molecule for the nine strongest lines.
Abstract: We describe the application of a new high-brightness, terahertz-beam system to time-domain spectroscopy. By analyzing the propagation of terahertz electromagnetic pulses through water vapor, we have made what we believe are the most accurate measurements to date of the absorption cross sections of the water molecule for the nine strongest lines in the frequency range from 0.2 to 1.45 THz.
830 citations
Journal Article•
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TL;DR: The absorption and scattering data show that for all wavelengths considered, scattering is much more important than absorption, and any quantitative dosimetry for skin treated with (laser) light is inaccurate.
Abstract: The current status of tissue optics is reviewed, distinguishing among the cases of dominant absorption, dominant scattering, and scattering about equal to absorption. Previously published data as well as some current unpublished data on (human) stratum corneum, epidermis, and dermis are collected and/or (re)analyzed in terms of absorption coefficient, scattering coefficient, and anisotropy scattering factor. It is found that the individual skin layers show strongly forward scattering (anisotropy factors between 0.7 and 0.9). The absorption and scattering data show that for all wavelengths considered, scattering is much more important than absorption. Solutions to the transport equation for a multilayer skin model and finite beam laser irradiation that take this into account are not yet available. Hence, any quantitative dosimetry for skin treated with (laser) light is inaccurate. >
804 citations
TL;DR: In this paper, a model was developed to resolve in situ phytoplankton absorption from a measured in situ total absorption spectrum which includes water, dissolved organics, particulate detritus, and phyto-worms, and was tested on a set of absorption spectra obtained from the productive waters around the San Juan Islands, Washington.
Abstract: Dissolved and suspended materials in the ocean modify the in-water light field by absorbing and scattering photons. Direct measurement of inherent optical properties of individual optical constituents is difficult since the constituents themselves cannot all be separated. A model was developed to resolve in situ phytoplankton absorption from a measured in situ total absorption spectrum which includes water, dissolved organics, particulate detritus, and phytoplankton. The model was tested on a set of absorption spectra obtained from the productive waters around the San Juan Islands, Washington. Results indicate that the model can predict the spectral shape of phytoplankton absorption (rz > 0.9) and total photon absorption by phytoplankton with ~27% error. Total photon absorption can be used to estimate phytoplankton absorption of light energy for improved primary production predictions, given submarine light field measurements or model calculations. Although developed for high chlorophyll waters, the model parameters are easily modified for vario&Casc 1 optical domains.
442 citations
TL;DR: A general criterion to describe this limitation that must be satisfied by all materials is derived and experimentally evaluated this criterion for a lead-glass fiber.
Abstract: Two-photon absorption can place a fundamental limitation on waveguide all-optical switching devices. We have derived a general criterion to describe this limitation that must be satisfied by all materials. As a specific example, we have experimentally evaluated this criterion for a lead-glass fiber.
424 citations
TL;DR: In this article, a computer method has been devised to describe the theoretical dissolution rate of a polydisperse powder under non-sink conditions based on its percent weight particle size distribution.
304 citations
TL;DR: The results show that, for the investigated tissues, extinction coefficients range from ~200 to 500 cm(-1) whereas absorption coefficients, depending on wavelength, vary from 0.2 to 25cm(-1).
Abstract: Optical properties of different human tissues in vitro have been evaluated by measuring extinction and absorption coefficients at 635- and 515-nm wavelengths and a scattering angular dependence at 635 nm. Extinction was determined by the on-axis attenuation of light transmitted through sliced specimens of various thicknesses. The absorption coefficient was determined by placing samples into an integrating sphere. The Henyey-Greenstein function was used for fitting experimental data of the scattering pattern. The purpose of this work was to contribute to the study of light propagation in mammalian tissues. The results show that, for the investigated tissues, extinction coefficients range from ~200 to 500 cm(-1) whereas absorption coefficients, depending on wavelength, vary from 0.2 to 25 cm(-1). Scattering is forward peaked with an average cosine of ~0.7.
241 citations
TL;DR: In this article, an indirect photometric detection method is described which is based on the use of an absorbing co-ion as the principal component of the background electrolyte, which is shown to be useful for detecting substances that have no optical absorption in the UV and/or visible region.
234 citations
TL;DR: In this paper, the theoretical factors governing the relationship between atomic absorption and atomic concentration are examined and the experimental problems involved in recording atomic absorption spectra are discussed, and it is shown that such spectra provide a promising method of chemical analysis with vital advantages over emission methods, particularly from the viewpoint of absolute analysis.
194 citations
TL;DR: In this paper, the authors present initial data from x-ray diffraction, ultraviolet-visible (UV-VIS) absorption, and infrared (IR) absorption spectroscopy measurements made during thermal cycling of unoriented, solution cast, poly(3-hexylthiophene) films.
TL;DR: In this article, low-resolution spectra have been obtained for a selection of infrared protostars and one object located behind the Taurus dark cloud and most of the differences in the spectra can be attributed to different H2O ice temperatures combined with additional broad absorption between 3.3 and 3.5 microns plus another absorption in the 2.8-2.9 micron range.
Abstract: Low-resolution spectra have been obtained for a selection of infrared protostars and one object located behind the Taurus dark cloud. Most of the differences in the spectra can be attributed to different H2O ice temperatures combined with additional broad absorption between 3.3 and 3.5 microns plus another absorption in the 2.8-2.9 micron range. An NH3-H2O ice mixture, scattering by H2O ice-coated grains, and hydrated silicates are ruled out as explanations for the last type of absorption. The most plausible explanation is still some form of hydrocarbon in the grain mantles.
TL;DR: In this paper, the propagation properties of suspended water and ice particles which make up atmospheric haze, fog, and clouds were examined for microwave and millimeter-wave frequencies, and the rates of attenuation alpha (dB/km) and delay tau (ps/km), derived from a complex refractivity based on the Rayleigh absorption approximation of Mie's scattering theory, were derived.
Abstract: Propagation properties of suspended water and ice particles which make up atmospheric haze, fog, and clouds were examined for microwave and millimeter-wave frequencies. Rates of attenuation alpha (dB/km) and delay tau (ps/km) are derived from a complex refractivity based on the Rayleigh absorption approximation of Mie's scattering theory. Key variables are particle mass content and permittivity, which depends on frequency and temperature both for liquid and ice states. Water droplet attenuation can be estimated within a restricted (10+or-10 degrees C) temperature range using a simple two-coefficient approximation. Experimental data on signal loss and phase delay caused by fog at four frequencies (50, 82, 141, and 246 GHz) over a 0.81-km line-of-sight path were found to be consistent with the model. >
TL;DR: In this paper, the fundamental optical absorption edge of V2O5 shifts to high energies by 0.20 − 0.31 eV as the lithium concentration increases from Li0.0V2O4 to Li0.86V2
Abstract: Electrochemical and spectroscopic measurements were used to characterize the electrochromic behavior of sputtered V2O5 films. In response to lithium intercalation, the fundamental optical absorption edge of V2O5 shifts to high energies by 0.20–0.31 eV as the lithium concentration increases from Li0.0V2O5 to Li0.86V2O5. There is a corresponding increase in the near‐infrared absorption that exhibits Beer’s law behavior at low lithium concentrations. The shift in absorption edge results in a large decrease in absorbance in the 350–450 nm wavelength range. This effect is most prevalent in thin films which exhibit a yellow to colorless optical modulation on lithium intercalation. The cathodic coloration in the near infrared is relatively weak with a maximum coloration efficiency of 35 cm2/C.
TL;DR: In this paper, an absorption spectrum containing both the XANES and the EXAFS region can be recorded in several seconds if x-ray monochromators at synchrotron beamlines are scanned continuously.
Abstract: An absorption spectrum containing both the XANES and the EXAFS region can be recorded in several seconds if x‐ray monochromators at synchrotron beamlines are scanned continuously. The experimental setups are described in detail. The accuracy of the method up to photon energies of 19 keV is demonstrated. Due to its advantages, the proposed approach may be used as an alternative to the energy dispersive EXAFS method, especially in the case of XANES spectroscopy.
01 Jan 1989
TL;DR: In this article, it was shown that the photochemical process is driven by absorption of photons by chlorophyll in the wavelength band from 400 to 700 nm, and that photosynthetic rate should more closely follow the number of photons absorbed rather than the amount of energy absorbed.
Abstract: Measurements of radiation in physiological ecology are of primary importance because of their role in energy balance determinations (see Chapter 7) and in photosynthesis measurements (see Chapter 11). Although less frequently made in physiological ecology, light quality measurements are important with respect to photomorphogenesis, or for understanding the effects of specific wavelengths, such as UV radiation, on physiological processes. Each of these measurements requires a different approach. In energy balance studies we are primarily interested in the energy incident on a leaf or plant, and how much of this energy is absorbed. Photosynthesis, on the other hand, is a photochemical process that is driven by absorption of photons by chlorophyll in the wavelength band from 400 to 700 nm. Here the absorptance of most leaves is quite high (Fig. 6.1). According to Planck’s law, the energy content of a 700 nm photon (171 kJ mol−1) is only 57% of that of a 400 nm photon (299 kJ mol−1). However, photosynthetic rate should be essentially independent of whether it was driven by the absorption of a photon of 400 or 700 nm light, despite the large difference in energy content. Any excess energy in the absorbed photon is dissipated as heat or fluorescence. Thus photosynthetic rate should more closely follow the number of photons absorbed rather than the amount of energy absorbed.
TL;DR: The extinction coefficient of a weak absorbing film can be extracted from special absorption using a simple formula, provided the substrate is a kind of glass of refractive index within the range of 1.5-1.7.
Abstract: The extinction coefficient of a weak absorbing film can be extracted from special absorption using a simple formula, provided the substrate is a kind of glass of refractive index within the range of 1.5-1.7.
TL;DR: Two-photon absorption of light with nonclassical (squeezed) fluctuations is considered and Mollow' derived the following expression for the twophoton absorption rate from a stationary field through second order in perturbation theory.
Abstract: Two-photon absorption of light with nonclassical (squeezed) fluctuations is considered. Several unique effects are predicted for various possible regimes. These include a linear (instead of quadratic) growth of the absorption rate with the light intensity for weak fields, the possibility of a decreasing absorption with increasing intensity, and orders-or-magnitude differences between absorption rates for phase- and amplitude-squeezed beams of the same intensity.
Patent•
25 Apr 1989
TL;DR: In this paper, an active medium, typically a photochromic material and more typically spirbenzopyran, maintained in a three-dimensional matrix, typically of polymer, is illuminated in selected regions by two UV laser light beams.
Abstract: An active medium, typically a photochromic material and more typically spirbenzopyran, maintained in a three-dimensional matrix, typically of polymer, is illuminated in selected regions by two UV laser light beams, typically of 532 nm. and 1064 nm. wavelength, to change from a first, spiropyran, to a second, merocyanine, stable molecular isomeric form by process of two-photon absorption. Regions not temporally and spatially coincidently illuminated are unchanged. Later illumination of the selected regions by two green-red laser light beams, typically of 1064 nm wavelength each, causes only the second, merocyanine, isomeric form to fluoresce. This fluorescence is detectable by photodetectors as stored binary data. The three-dimensional memory may be erased by heat, or by infrared radiation, typically 2.12 microns wavelength. Use of other medium permit the three-dimensional patterning of three-dimensional forms, such as polystyrene polymer solids patterned from liquid styrene monomer. Three-dimensional displays, or other inhomogeneity patterns, can also be created.
TL;DR: In this paper, the authors present a new model for two-beam coupling in photorefractive semiconductors under an external dc field E0. This model predicts that the exponential gain Γ can exhibit an intensitydependent resonant behavior, yielding a π/2 phase shift of the space charge field with respect to the incident fringe pattern.
Abstract: We present a new model (including both temperature and electron‐hole effects) of two‐beam coupling in photorefractive semiconductors under an external dc field E0. This model predicts that the exponential gain Γ can exhibit an intensity‐dependent resonant behavior, yielding a π/2 phase shift of the space‐charge field with respect to the incident fringe pattern. This optimum intensity strongly depends on crystal temperature but it is practically independent of the grating period. As an illustration this model is applied to InP:Fe. In this case the resonance occurs when the hole photoionization rate and the electron thermal emission rate are equal. Values of Γ as high as 20 cm−1 at 1.06 μm, for a fringe spacing of 15 μm and E0 =10 kV/cm, are predicted. The comparison between theory and experimental data requires taking into account the variation of the pump intensity throughout the sample (due to optical absorption), which reduces the volume where the resonance condition is fulfilled; in this way a satisfac...
TL;DR: In this paper, a femtosecond differential absorption measurements of the quantum-confined transitions in CdSe microcrystallites are reported, which are consistently explained by bleaching of one-pair states and induced absorption caused by photoexcited two electron-hole pair states.
Abstract: Femtosecond differential absorption measurements of the quantum-confined transitions in CdSe microcrystallites are reported. Spectral hole burning is observed, which is accompanied by an induced absorption feature on the high-energy side. The spectral position of the burned hole depends on the excitation wavelength. For excitation on the low-energy side of the lowest quantum-confined transition, a slight shift of the hole towards the line center is observed. The hole width increases with pump intensity and the magnitude of the induced transparency saturates at the highest excitation level. The results are consistently explained by bleaching of one-pair states and induced absorption caused by the photoexcited two electron-hole pair states. It is concluded that the presence of one electron in the excited state prevents further absorption of photons at the pair-transition energy and accounts for the major portion of the bleaching of the transition. >
TL;DR: In this paper, the Hall effect and the strength of localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E1 band gap were investigated.
Abstract: n‐type silicon‐doped epitaxial layers of gallium arsenide grown by molecular‐beam epitaxy (MBE) or metal‐organo chemical vapor deposition (MOCVD) have been investigated by measurements of the Hall effect and the strengths of the localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E1 band gap. Lines from Si(Ga) donors, Si(As) acceptors, Si(Ga)‐Si(As) pairs, and Si‐X, a complex of silicon with a native defect, were detected and correlated for the two techniques. The maximum carrier concentration [n] found for samples grown under standard conditions was 5.5×1018 cm−3. At higher doping levels Si‐X becomes dominant and acts as an acceptor, so reducing [n]. An integrated absorption of 1 cm−2 in the Si(Ga) LVM line corresponds to 5.0±4×1016 atoms cm−3: a similar calibration applies to the Si(As) line, but for Si‐X, an absorption of 1 cm−2 corresponds to only 2.7±1.0×1016 defects cm−3. Possib...
TL;DR: In this paper, the authors studied the heating of coronal loops by resonant absorption of Alfven waves in compressible, resistive magnetohydrodynamics and derived the intrinsic dissipation spectrum independent of the external driver.
Abstract: The heating of coronal loops by resonant absorption of Alfven waves is studied in compressible, resistive magnetohydrodynamics. The loops are approximated by straight cylindrical, axisymmetric plasma columns and the incident waves which excite the coronal loops are modelled by a periodic external driver. The stationary state of this system is determined with a numerical code based on the finite element method. Since the power spectrum of the incident waves is not well known, the intrinsic dissipation is computed. The intrinsic dissipation spectrum is independent of the external driver and reflects the intrinsic ability of the coronal loops to extract energy from incident waves by the mechanism of resonant absorption. The numerical results show that resonant absorption is very efficient for typical parameter values occurring in the loops of the solar corona. A considerable part of the energy supplied by the external driver, is actually dissipated Ohmically and converted into heat. The heating of the plasma is localized in a narrow resonant layer with a width proportional to η
1/3. The energy dissipation rate is almost independent of the resistivity for the relevant values of this parameter. The efficiency of the heating mechanism and the localization of the heating strongly depend on the frequency of the external driver. Resonant absorption is extremely efficient when the plasma is excited with a frequency near the frequency of a so-called ‘collective mode’.
TL;DR: In this article, the authors presented ultra-violet visible optical absorption spectra of thin solid films of four poly(3-alkylthiophenes) between 10 K and room temperature.
TL;DR: In this article, transient optical absorption spectroscopy has been used for the first time to study the transport of ground state Y, Ba, Cu, and Ba+ following excimer laser ablation of Y1Ba2Cu3O7−x pellets.
Abstract: Transient optical absorption spectroscopy has been utilized for the first time to study the transport of ground‐state Y, Ba, Cu, and Ba+ following excimer laser ablation of Y1Ba2Cu3O7−x pellets. Spectral broadening of the atomic lines monitored in both absorption and emission is reported, indicating the existence of gas phase collisions in the plume of ejected material. Time‐of‐flight velocity distributions of the nonemitting neutrals and ions determined by the absorption technique are broadened and shifted to lower velocities than the velocity distributions inferred from excited‐state fluorescence in the plume. Absorption by ground‐state Y+, YO, BaO, and CuO also has been observed with this technique. The absorption technique, and its application as an in situ monitor of neutral and ion transport during deposition of superconducting thin films, is described.
TL;DR: In this paper, new experimental features of the field-modulated microwave absorption in high-Tc ceramic superconductors are presented, and a model for the loss mechanism can explain the complicated field and temperature dependences of the absorption signals.
Abstract: New experimental features of the field-modulated microwave absorption in high-Tc ceramic superconductors are presented. The proposed model for the loss mechanism can explain the complicated field and temperature dependences of the absorption signals.
TL;DR: The absorption of X-rays and gamma-rays in interactions with the cosmic thermal background and baryonic matter at cosmological redshifts is studied in this paper, where analytical formulae for the optical depths to photoionization, Compton scattering, photon-matter pair production, and photon-photon scattering are derived as functions of redshift and photon energy.
Abstract: The absorption of X-rays and gamma-rays in interactions with the cosmic thermal background and baryonic matter at cosmological redshifts is studied. Analytical formulae for the optical depths to photoionization, Compton scattering, photon-matter pair production, photon-photon scattering, and photon-photon single- and double-pair production are derived as functions of redshift and photon energy. The redshift-energy plane is divided into regions of dominance of various absorption processes. In particular, it is found that photon-photon scattering (a process not previously considered in astrophysics) is important for certain ranges of photon energy and redshift. 55 refs.