Showing papers on "Absorption (electromagnetic radiation) published in 1997"
TL;DR: Definitive data on the absorption spectrum of pure water from 380 to 700 nm have been obtained with an integrating cavity technique and several spectroscopic features have been identified in the visible spectrum to the knowledge for the first time.
Abstract: Definitive data on the absorption spectrum of pure water from 380 to 700 nm have been obtained with an integrating cavity technique. The results are in good agreement with those recently obtained by our group with a completely independent photothermal technique. As before, we find that the absorption in the blue is significantly lower than had previously been generally believed and that the absorption minimum is at a significantly shorter wavelength, i.e., 0.0044 ? 0.0006 m(-1) at 418 nm. Several spectroscopic features have been identified in the visible spectrum to our knowledge for the first time.
2,134 citations
TL;DR: The surface-enhanced infrared absorption (SEIRA) as mentioned in this paper is a surface analytical tool that is very useful for in situ studies of electrode/electrolyte interfaces.
Abstract: Molecules adsorbed on evaporated thin metal films exhibit enormously strong infrared absorption. The thin metal films that exhibit the surface-enhanced infrared absorption (SEIRA) consist of metal particles much smaller than the wavelength of light. Electric field associated with the incident infrared radiation is enhanced via the excitation of localized plasmon of the particles, yielding the absorption enhancement. Preferential orientation and the change in absorption coefficient of molecules caused by chemisorption onto the metal surface provide additional enhancement. Most characteristic observations in SEIRA experiments are well explained by a simple electromagnetic theory. The infrared spectroscopy utilizing the SEIRA effect is promising as a new surface analytical tool. In particular, it is very useful for in situ studies of electrode/electrolyte interfaces. By the combined use of the attenuated-total-reflection technique, reactions and adsorption/desorption of molecules at the interfaces can be inv...
568 citations
TL;DR: In this paper, the interaction of a 1053 nm picosecond laser pulse with a solid target has been studied for focused intensities of up to 1019 W cm−2.
Abstract: The interaction of a 1053 nm picosecond laser pulse with a solid target has been studied for focused intensities of up to 1019 W cm−2. The maximum ion energy cutoff Emax (which is related to the hot electron temperature) is in the range 1.0–12.0 MeV and is shown to scale as Emax≈I1/3. The hot electron temperatures were in the range 70–400 keV for intensities up to 5×1018 W cm−2 with an indication of a high absorption of laser energy. Measurements of x-ray/γ-ray bremsstrahlung emission suggest the existence of at least two electron temperatures. Collimation of the plasma flow has been observed by optical probing techniques.
531 citations
TL;DR: In this paper, the authors demonstrate that a commercial single-frequency cavity ring down spectroscopy (CRDS) can also be conveniently employed, allowing to gain in spectral resolution, signal intensity and data acquisition rate.
512 citations
TL;DR: In the absence of scatter, the total light absorption in the medium is a linear sum of that due to each chromophore as discussed by the authors, and this linear summation is distorted because the optical path length at each wavelength may differ.
Abstract: In near–infrared spectroscopy (NIRS) of tissue, light attenuation is due to: (i) absorption from chromophores of fixed concentration, (ii) absorption from chromophores of variable concentration, and (iii) light scatter. NIRS is usually concerned with trying to quantify the concentrations of chromophores in category (ii), in particular oxy– and deoxyhaemoglobin (HbO2 and Hb) and cytochrome oxidase.
In the absence of scatter the total light absorption in the medium is a linear sum of that due to each chromophore. In a scattering medium like tissue, this linear summation is distorted because the optical path length at each wavelength may differ. This distorted spectrum is then superimposed upon a further wavelength–dependent attenuation arising from light loss due to scatter, which is a complex function of the tissue absorption and scattering coefficients ( μ a and μ s), scattering phase function, and tissue and measurement geometry. Consequently, quantification of NIRS data is difficult.
Over the past 20 years many differing approaches to quantification have been tried. The development of methods for measuring optical path length in tissue initially enabled changes in concentration to be quantified, and subsequently methods for absolute quantification of HbO2 and Hb were developed by correlating NIRS changes with an independent measurement of arterial haemoglobin saturation. Absolute determination of tissue optical properties, however, requires additional information over and above the detected intensity at the tissue surface, which must then be combined with a model of light transport to derive μ a and μ s. The additional data can take many forms, e.g. the change in intensity with distance, the temporal dispersion of light from an ultrashort input light pulse, or phase, and modulation depth changes of intensity–modulated light. All these approaches are now being actively pursued with considerable success. However, all the approaches are limited by the accuracy of the light transport models, especially in inhomogeneous media.
504 citations
TL;DR: Field measurements support the temperature and salinity dependencies found in the laboratory both in the near infrared and at shorter wavelengths.
Abstract: We have measured the absorption coefficient of pure and salt water at 15 wavelengths in the visible and near-infrared regions of the spectrum using WETLabs nine-wavelength absorption and attenuation meters and a three-wavelength absorption meter. The water temperature was varied between 15 and 30 degrees C, and the salinity was varied between 0 and 38 PSU to study the effects of these parameters on the absorption coefficient of liquid water. In the near-infrared portion of the spectrum the absorption coefficient of water was confirmed to be highly dependent on temperature. In the visible region the temperature dependence was found to be less than 0.001 m-1 degrees C except for a small region around 610 nm. The same results were found for the temperature dependence of a saltwater solution. After accounting for index-of-refraction effects, the salinity dependence at visible wavelengths is negligible. Salinity does appear to be important in determining the absorption coefficient of water in the near-infrared region. At 715 nm, for example, the salinity dependence was -0.00027 m-1 /PSU. Field measurements support the temperature and salinity dependencies found in the laboratory both in the near infrared and at shorter wavelengths. To make estimates of the temperature dependence in wavelength regions for which we did not make measurements we used a series of Gaussian curves that were fit to the absorption spectrum in the visible region of the spectrum. The spectral dependence on temperature was then estimated based on multiplying the Gaussians by a fitting factor.
470 citations
TL;DR: This review describes a relatively new direct absorption technique that is developed for measuring the electronic spectra of jet-cooled molecules and clusters with both high sensitivity and high spectral resolution.
Abstract: The measurement of electronic spectra of supersonically cooled molecules and clusters is a widely used approach for addressing many problems in chemistry. The most established techniques for making such measurements are laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI), and both have been employed very successfully in a large number of studies. However, both methods often fail for systems containing more than a few atoms, due to rapid internal conversion, predissociation, or other dynamical processes. Even for small systems, the vibronic band intensities are often contaminated by intramolecular relaxation dynamics; in such cases, these techniques cannot be used for reliable intensity measurements. For clusters that exhibit rapid photofragmentation, depletion spectroscopy can be employed quite effectively to measure their vibronic structure, but again, dynamic effects complicate the interpretation of spectra. The same considerations apply to other types of “action” spectroscopy. It would often be preferable to measure the electronic spectra of molecules and clusters in direct absorption, as this approach is the most straightforward and accurate means of determining absolute vibronic band intensities and for accessing states that are invisible to LIF or REMPI. The problem, of course, is that direct absorption methods are generally orders of magnitude less sensitive than the “action” techniques and are, therefore, difficult to apply to transient species, such as clusters or radicals. In this review, we describe a relatively new direct absorption technique that we have developed for measuring the electronic spectra of jet-cooled molecules and clusters with both high sensitivity and high spectral resolution. The method is based on measurement of the time rate of decay of a pulse of light trapped in a high reflectance optical cavity; we call it cavity ringdown laser absorption spectroscopy (CRLAS). In practice, pulsed laser light is injected into an optical cavity that is formed by a pair of highly reflective (R > 99.9%) mirrors. The small amount of light that is now trapped inside the cavity reflects back and forth between the two mirrors, with a small fraction (∼1 R) transmitting through each mirror with each pass. The resultant transmission of the circulating light is monitored at the output mirror as a function of time and allows the decay time of the cavity to be determined. A simple picture of the cavity decay event for the case where the laser pulse is temporally shorter than the cavity round trip transit time is presented in Figure 1. In this case, the intensity envelope of these discrete transmitted pulses exhibits a simple exponential decay. The time required for the cavity to decay to 1/e of the initial output pulse is called the “cavity ringdown” time. Determination of the ringdown time allows the absolute single pass transmission coefficient of the cavity to be determined with high accuracy, given the mirror spacing. The apparatus is converted to a sensitive absorption spectrometer simply by placing an absorbing medium between the two mirrors and recording the frequency dependent ringdown time of the cavity. Ideally, the ringdown time is a function of only the mirror reflectivities, cavity dimensions, and sample absorption. Absolute absorption intensities are obtained by subtracting the base-line transmission of the cavity, which is determined when the laser wavelength is off-resonance with all molecular transitions. † IBM Predoctoral Fellow. Current address: Sandia National Laboratories, M/S 9055, Livermore, CA 94551-0969. ‡ Los Gatos Research. 25 Chem. Rev. 1997, 97, 25−51
421 citations
TL;DR: In this paper, the spectroscopic behavior of colloidal InP quantum dots (QDs) has been investigated as a function of the mean QD diameter (which ranged from 26 to 60 A).
Abstract: The spectroscopic behavior of colloidal InP quantum dots (QDs) has been investigated as a function of the mean QD diameter (which ranged from 26 to 60 A). Absorption spectra show up to three peaks or shoulders which reflect excited state transitions in the QDs. Global photoluminescence (PL) spectra (excitation well to the blue of the absorption onset and which consequently excites most of the QDs in the size distribution) show broad PL emission. The emission and absorption features shift to higher energy with decreasing QD size. Resonant PL spectra (size-selective excitation into the tail of the absorption onset) show increasing fluorescence line narrowing with increasing excitation wavelength; PL and photoluminescence excitation spectroscopy were used to derive the PL red shift as a function of QD size. The resonant red shifts for QDs of a single size were extracted from PL data that reflect the emission from an ensemble of QD diameters. An analysis of the single-dot resonant red shift (difference betwee...
356 citations
TL;DR: In this article, the authors studied absorption mechanisms for ultra-intense (I>10/sup 17/W/cm/sup 2/) laser pulses incident on solids and overdense plasma slabs.
Abstract: Absorption mechanisms for ultra-intense (I>10/sup 17/ W/cm/sup 2/) laser pulses incident on solids and overdense plasma slabs are discussed. We focus on the ultrashort pulse regime, i.e., where the laser pulse length is only a few to perhaps thousands of femtoseconds. Starting from well-known results at low intensity and long pulse length, we begin with absorption mechanisms such as inverse Bremstrahlung and classical resonance absorption and survey several additional absorption mechanisms significant for ultrashort, ultra-intense laser light interacting with overdense plasmas. Estimates for the fraction of laser energy absorbed by various mechanisms are given. It is found that the fraction of energy absorbed by the plasma, and the resulting electron temperatures, can depend considerably on the scale length of the plasma at the critical surface. It is also found that two-dimensional (2-D) effects greatly increase the amount of absorption into hot electrons, over the amount predicted using one-dimensional (1-D) theory. The inclusion of kinetic effects, collisionless absorption, and multidimensional effects are crucial to obtaining a complete picture of the interaction. We also review some of the experimental efforts to understand this complex process of absorption.
350 citations
TL;DR: In this article, an initial molecular excited state is generated in the host compound by absorption of light; this state is then resonantly and non-radiatively transferred down in energy (through one or more steps) between suitably matched dye molecules, so ensuring that the absorption losses at the final emission wavelengths are very small.
Abstract: There is currently renewed interest in the development of lasers using solid-state organic and polymeric materials as the gain media. These materials have a number of properties that make them good candidates for such applications — for example, emission bands that are displaced (via a Stokes shift) from absorption bands, and the ease with which the emitting species can be embedded in a suitable host material1,2,3,4,5. But despite these advantages, the threshold power densities required for light amplification that have been reported so far have been high6,7,8. Here we describe an approach, based on energy transfer between molecular species, that can lower the threshold for stimulated emission and laser action while improving markedly the waveguiding properties of the active material. In our materials, an initial molecular excited state is generated in the host compound by absorption of light; this state is then resonantly and non-radiatively transferred down in energy (through one or more steps) between suitably matched dye molecules dispersed in the host, so ensuring that the absorption losses at the final emission wavelengths are very small. Such composite gain media provide provide broad tunability of the emission wavelength, and also decouple the optical emission properties from the transport properties, so providing greater flexibility for the design of future electrically driven device structures.
331 citations
TL;DR: In this paper, an elementary empirical model for the distribution of electronic states of an amorphous semiconductor is presented, and the functional form of the optical absorption spectrum is determined, focusing on the joint density of states function, which dominates the absorption spectrum over the range of photon energies.
Abstract: An elementary empirical model for the distribution of electronic states of an amorphous semiconductor is presented. Using this model, we determine the functional form of the optical absorption spectrum, focusing our analysis on the joint density of states function, which dominates the absorption spectrum over the range of photon energies we consider. Applying our optical absorption results, we then determine how the empirical measures commonly used to characterize the absorption edge of an amorphous semiconductor, such as the Tauc gap and the absorption tail breadth, are related to the parameters that characterize the underlying distribution of electronic states. We, thus, provide the experimentalist with a quantitative means of interpreting the physical significance of their optical absorption data.
TL;DR: In this article, the optical properties of novel semiconductor nanosheets of Ti1-δ□δO24δ- (δ ∼ 0.09; □, vacancy) were obtained by delaminating a layered titanate into elementary host layers.
Abstract: We have studied the optical properties of novel semiconductor nanosheets of Ti1-δ□δO24δ- (δ ∼ 0.09; □, vacancy) which were obtained by delaminating a layered titanate into elementary host layers. A uniform thickness in subnanometer scale as well as high crystallinity resulted in a sharp absorption onset with a well-developed peak assignable to excitonic transition. The absorption was pronouncedly blue shifted (>1.4 eV) relative to the band edge for bulk TiO2, which is attributed to size quantization effects. Room-temperature photoluminescence spectra showed resonant emission and well-structured fluorescence extending into a lower energy region.
TL;DR: In this paper, the authors measured the energy absorption efficiency of high intensity, picosecond laser pulses in low density gases composed of large atomic clusters and found that even though the average density of the resulting plasmas is low, energy absorption can be very high, indicating that substantial laser energy is deposited per particle in the plasma.
Abstract: We have measured the energy absorption efficiency of high intensity, picosecond laser pulses in low density gases composed of large atomic clusters. We find that, though the average density of the resulting plasmas is low, the energy absorption can be very high $(g95%)$, indicating that substantial laser energy is deposited per particle in the plasma. Ion energy measurements confirm that this efficient energy deposition results in plasmas with very high (multi-keV) ion temperatures.
TL;DR: It was found that the rate at which the thermal dose was applied plays a very important role in the total attenuation absorption, and lower thermal dose rates resulted in larger attenuation coefficients.
Abstract: The effect of temperature and thermal dose (equivalent minutes at 43 °C) on ultrasonic attenuation in fresh dog muscle, liver, and kidney in vitro, was studied over a temperature range from room temperature to 70 °C. The effect of temperature on ultrasonic absorption in muscle was also studied. The attenuation experiments were performed at 4.32 MHz, and the absorption experiments at 4 MHz. Attenuation and absorption increased at temperatures higher than 50 °C, and eventually reached a maximum at 65 °C. The rate of change of tissue attenuation as a function of temperature was between 0.239 and 0.291 Np m−1 MHz−1 °C−1 over the temperature range 50–65 °C. A change in attenuation and absorption was observed at thermal doses of 100–1000 min, where a doubling of these loss coefficients was observed over that measured at 37 °C, presumably the result of changes in tissue composition. The maximum attenuation or absorption was reached at thermal dosages on the order of 107 min. It was found that the rate at which t...
TL;DR: In this paper, a new structure of dye-sensitized nanocrystalline photoelectrochemical cell, which permits effective absorption of incident solar energy using thinner dye sensitized film, is proposed based on theoretical examination.
TL;DR: A steady-state radially resolved diffuse reflectance spectrometer capable of measuring the absorption and transport scattering spectra of tissue-simulating phantoms over an adjustable 170-nm wavelength interval in the visible and near infrared is presented.
Abstract: We present a steady-state radially resolved diffuse reflectance spectrometer capable of measuring the absorption and transport scattering spectra of tissue-simulating phantoms over an adjustable 170-nm wavelength interval in the visible and near infrared. Measurements in a variety of phantoms are demonstrated over the relevant range of tissue optical properties, and the accuracy of the instrument is found to be approximately 10% in both scattering and absorption. Monte Carlo simulations designed to test the accuracy of the instrument are presented that support the experimental findings.
TL;DR: In this article, the spectral signatures (both absorption and fluorescence) of settled sewage samples collected as 24-h composites from three different treatment works were found to be similar, having an absorption band at around 280 nm and a fluorescence maximum at 340 nm (using 280 nm excitation).
TL;DR: In this article, the authors observed a 50% reduction in absorption between the subband resonances which can be explained by taking into account the coherent coupling of the upper states, analogous to electromagnetically induced transparency (EIT) in atomic systems.
Abstract: We report the observation of tunneling induced transparency in asymmetric double quantum well structures. Resonant tunneling through a thin barrier is used to coherently couple the two upper states in a three level system of electronic subbands in a GaAs/AlGaAs structure. This creates Fano-type interferences for the collective intersubband excitations in the absorption from the ground state, analogous to electromagnetically induced transparency (EIT) in atomic systems. We observe a 50% reduction in absorption between the subband resonances which can be explained by taking into account the coherent coupling of the upper states. We analyze the bias dependent absorption spectra and determine the relevant lifetime broadening and dephasing rates for the transitions.
TL;DR: In this article, the photoresponse of a uni-traveling-carrier photodiode (UTC-PD), which is configured with a neutral narrow-gap light absorption layer and a depleted wide-gap carrier collecting layer, is investigated by small-signal analysis.
Abstract: The photoresponse of a uni-traveling-carrier photodiode (UTC-PD), which is configured with a neutral narrow-gap light absorption layer and a depleted wide-gap carrier collecting layer, is investigated by small-signal analysis. Drift-diffusion model was used for analyzing carrier dynamics in the absorption layer. For accurately predicting the frequency response, a boundary condition at the edge of the absorption layer was carefully treated by taking into account the electron thermionic emission velocity. High electron mobility in the absorption layer and high drift velocity in the carrier collecting layer associated with the velocity overshoot effect are both essential for short response times. Calculations performed on InP/InGaAsP UTC-PDs with the same absorption and carrier collecting layer thicknesses show that the response can be dominated by the electron transport in the absorption layer provided that the significant velocity overshoot occurs in the carrier collecting layer. Furthermore, a UTC-PD with a quasi-field in the absorption layer can generate a several times broader bandwidth than conventional pin PDs, while maintaining a similar internal quantum efficiency.
TL;DR: In this paper, a broad absorption band around 500 nm is observed in ZnS nanoparticles and the absorption becomes more intensive and shifts to the blue as the particle size is decreased.
Abstract: A broad absorption band around 500 nm is observed in ZnS nanoparticles. The absorption becomes more intensive and shifts to the blue as the particle size is decreased. The absorption energy is lower than the band gap of the particles and is considered to be caused by the surface states. This assignment is supported by the results of the fluorescence and of the thermoluminescence of the surface states. Both the absorption and the fluorescence reveal that the surface states are size dependent. The glow peak of the semiconductor particles is not varied as much upon decreasing size, indicating the trap depth of the surface states is not sensitive to the particle size. Considering these results, a new model on the size dependence of the surface states is proposed, which may explain our observations reasonably.
TL;DR: In this paper, the authors used hydrodynamical simulations to investigate the spatial distribution and absorption properties of metal-enriched gas in such regions of ongoing galaxy formation, and observed column density ratios of different ionic species at z = 3 can be well reproduced if a mean metallicity [Z/H] = -2.5, relative abundances as found in metal-poor stars, a UV background with intensity J-22 = 3 at the Lyman limit, and either a power-law spectrum (J ∝ ν-1.5) or the
Abstract: In a hierarchical cosmogony, galaxies build up by continuous merging of smaller structures. At z = 3, the matter content of a typical present-day galaxy is dispersed over several individual clumps embedded in sheetlike structures, often aligned along filaments. We have used hydrodynamical simulations to investigate the spatial distribution and absorption properties of metal-enriched gas in such regions of ongoing galaxy formation. The metal and hydrogen absorption features produced by the collapsing structures closely resemble observed QSO absorption systems over a wide range in H I column density. Strong C II and Si IV absorption occurs for lines of sight passing the densest regions close to the center of the protogalactic clumps, while C IV is a good tracer of the prominent filamentary structures and O VI becomes the strongest absorption feature for lines of sight passing through low-density regions far away from fully collapsed objects. The observed column density ratios of the different ionic species at z = 3 can be well reproduced if a mean metallicity [Z/H] = -2.5, relative abundances as found in metal-poor stars, a UV background with intensity J-22 = 3 at the Lyman limit, and either a power-law spectrum (J ∝ ν-1.5) or the spectral shape proposed by Haardt & Madau are assumed. The observed scatter in [C/H] is about a magnitude larger than that in the simulations, which suggests an inhomogeneous metal distribution. Observed and simulated Doppler parameter distributions of H I and C IV absorption lines are in good agreement, which indicates that shock heating due to gravitational collapse is a second important heating agent in addition to photoionization heating. The large velocity spreads seen in some C IV systems may be due to the occasional alignments of the observer's line of sight with expanding large-scale filaments. Both high-ionization multicomponent heavy-element absorbers and damped Lyα systems can arise from groups of moderately sized protogalactic clumps (Mbaryon ~ 109 M☉). Recent detections of star-forming galaxies at similar redshifts are consistent with this picture.
TL;DR: In this paper, the authors used ringdown laser absorption spectroscopy (IR-CRLAS) to determine the absolute concentrations of water dimers, trimers, tetramers, and pentamers in a pulsed supersonic expansion for the first time.
Abstract: The recently developed technique of infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) has been employed in the 3.0 μm region to determine the absolute concentrations of water dimers, trimers, tetramers, and pentamers in a pulsed supersonic expansion for the first time. Additional spectral features are reported, one of which we assign to the bound O−H stretching bands of the hexamer. Additionally, by simple variation of the jet stagnation pressure, the collective O−H stretching absorption from all clusters produced in the expansion was observed to change from that of discrete features of small clusters to band profiles of liquid water and finally to amorphous ice.
TL;DR: In this paper, a simple model is presented to describe the effects of light scattering particles on the specific attenuation cross-section, which relates the attenuation of light by a particleloaden quartz fiber filter to the black carbon (BC) content of deposited fine dust.
TL;DR: In this paper, the C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been recorded using transmission, fluorescence, and electron yield detection.
Abstract: The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been recorded using transmission, fluorescence, and electron yield detection. The corresponding electron energy loss spectra (EELS) have been recorded in a scanning transmission electron microscope. These results are compared to the C 1s and O 1s spectra of gas phase 1,4-dimethyl terephthalate (the monomer of PET) recorded using EELS. The comparison of monomer and polymer materials in different phases and with different techniques has aided the understanding of the relative strengths and limitations of each technique as well as assisting the spectral interpretation. Good agreement is found in the overall shape and the energies of the spectral features. Relatively minor differences in intensities can be understood in terms of the properties of the individual spectroscopic techniques. The critical dose for radiation damage by 100 keV electrons incident on PET at 100 K is found to be (1.45 ± 0.15) × 103 eV nm-3. In contrast...
TL;DR: It is demonstrated, using both Monte Carlo simulations and experimental measurements, that for an appropriate separation between light-delivery and light-collection fibers the path length of the collected photons does not depend on scattering parameters for the range of parameters typically found in tissue.
Abstract: The noninvasive measurement of variations in absorption that are due to changes in concentrations of biochemically relevant compounds in tissue is important in many clinical settings. One problem with such measurements is that the path length traveled by the collected light through the tissue depends on the scattering properties of the tissue. We demonstrate, using both Monte Carlo simulations and experimental measurements, that for an appropriate separation between light-delivery and light-collection fibers the path length of the collected photons does not depend on scattering parameters for the range of parameters typically found in tissue. This is important for developing rapid, noninvasive, and inexpensive methods for measuring absorption changes in tissue.
TL;DR: In this article, the absorption of a weak probe beam for a V-type atom with a closely spaced doublet was examined and it was shown that quantum interference between the two excitation pathways can result in very narrow resonances, transparency, and even gain without population inversion.
Abstract: We examine the absorption of a weak probe beam for a V-type atom with a closely spaced doublet and demonstrate that quantum interference between the two excitation pathways can result in very narrow resonances, transparency, and even gain without population inversion. The origin of these effects is discussed.
TL;DR: In this article, the authors presented results from Keck I high-resolution spectroscopy of the radio loud quasar PKS 0123+257 (PKS 01 23+257) at a redshift of 2.369 and showed that the absorption lines are positioned near the centers of the broad emission lines.
Abstract: We present results from Keck I high resolution spectroscopy of the radio loud quasar PKS 0123+257 ($z_e$=2.364, V=17.5). In this object we detect Ly$\alpha$, N V 1238,1242, Si IV 1393,1402, and C IV 1548,1550 in an absorption system at a redshift of 2.369. The Ly$\alpha$ line has a square- bottomed profile suggesting a high column density of gas, yet the line does not reach zero intensity. The resolved C IV doublet ratio also clearly demonstrates that the absorbing clouds at this redshift do not fully occult the background light source along our line-of-sight.
The absorption lines are positioned near the centers of the broad emission- lines and the coverage fraction of the strongest absorption lines varies inversely proportionally with the strength of the corresponding emission lines. This implies that although the absorption-line region may obscure the continuum source, it does not completely occult the broad emission-line region. This effect suggests that the lines are formed close to the QSO central region. A model is proposed in which the apparent coverage fraction derived for the weaker absorption lines may vary with the column density of the lines.
Broad absorption-lines (which are known to be intrinsic) are found nearly exclusively in radio-quiet objects. Intrinsic narrow absorption lines have previously been found in radio quiet QSOs; it is therefore significant that an intrinsic absorption system has been verified in a radio loud quasar.
TL;DR: The ANSI/ASA S1.26-2014 standard as discussed by the authors provides the means to calculate atmospheric absorption losses of sound from any source, moving or stationary, for a wide range of meteorological conditions.
Abstract: This Standard provides the means to calculate atmospheric absorption losses of sound from any source, moving or stationary, for a wide range of meteorological conditions. The atmosphere is assumed to be still, homogeneous moist air of normal composition. Non-homogeneous atmospheres can be divided into horizontal layers within which homogeneous conditions can be assumed. Attenuation coefficients for puretone sounds are calculated by means of equations (or a table) over ranges of frequency, and the humidity, pressure, and temperature of the atmosphere. For sounds analyzed by fractional-octave-band filters (e.g., one-third-octave-band filters), alternative methods are provided in annexes to calculate the attenuation caused by atmospheric absorption from that specified for pure-tone sounds. This is a preview of \"ANSI/ASA S1.26-2014 ...\". Click here to purchase the full version from the ANSI store.
TL;DR: In this article, the excitation of the luminescence induced in rare earth ion activators doped in LiYF4, LaF3 and YF3 was recorded in a wide continuous spectral region from 5 to 15 eV using synchrotron radiation as a photon source.
TL;DR: In this article, the coupled wave theory of Kogelnik was extended to the case of moderately absorbing anisotropic materials with grating vector and medium boundaries arbitrarily oriented with respect to the main axes of the optical indicatrix.
Abstract: The coupled wave theory of Kogelnik [H. Kogelnik, Bell Syst. Tech. J. 48, 2909 (1969)] is extended to the case of moderately absorbing thick anisotropic materials with grating vector and medium boundaries arbitrarily oriented with respect to the main axes of the optical indicatrix. Dielectric and absorption modulation with common grating vector and of arbitrary relative phase shift is considered. Solutions for the wave amplitudes, diffraction efficiencies, and angular mismatch sensitivities are given in transmission and reflection geometries. The main difference of the new results with respect to the expressions valid for isotropic media arise due to the walk-off between the wave-front and energy propagation directions. The difference is particularly important in materials with large birefringence, such as organic crystals, ordered polymers, and liquid crystalline cells. The special case of Bragg diffraction and two-beam coupling at holograms recorded in optically inactive photorefractive crystals is analyzed in detail. It is found that the two-beam coupling gain is influenced substantially by an absorption anisotropy.