Showing papers on "Absorption (electromagnetic radiation) published in 1988"
TL;DR: In this paper, the authors have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources.
Abstract: We have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources. The technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined within a closed optical cavity. The decay of the light intensity within the cavity is a simple exponential with loss components due to mirror loss, broadband scatter (Rayleigh, Mie), and molecular absorption. Narrowband absorption spectra are recorded by scanning the output of a pulsed laser (which is injected into the optical cavity) through an absorption resonance. We have demonstrated the sensitivity of this technique by measuring several bands in the very weak forbidden b1Σg−X3Σg transition in gaseous molecular oxygen. Absorption signals of less than 1 part in 106 can be detected.
1,540 citations
TL;DR: In this article, a 60-femtosecond pump pulse at 618 nanometers was used to study the primary photoprocesses in the light-driven transmembrane proton pump bacteriorhodopsin.
Abstract: Femtosecond optical measurement techniques have been used to study the primary photoprocesses in the light-driven transmembrane proton pump bacteriorhodopsin. Light-adapted bacteriorhodopsin was excited with a 60-femtosecond pump pulse at 618 nanometers, and the transient absorption spectra from 560 to 710 nanometers were recorded from -50 to 1000 femtoseconds by means of 6-femtosecond probe pulses. By 60 femtoseconds, a broad transient hole appeared in the absorption spectrum whose amplitude remained constant for about 200 femtoseconds. Stimulated emission in the 660- to 710-nanometer region and excited-state absorption in the 560- to 580-nanometer region appeared promptly and then shifted and decayed from 0 to approximately 150 femtoseconds. These spectral features provide a direct observation of the 13-trans to 13-cis torsional isomerization of the retinal chromophore on the excited-state potential surface. Absorption due to the primary ground-state photoproduct J appears with a time constant of approximately 500 femtoseconds.
497 citations
TL;DR: Difficulties of quantitation of hemoglobin/myoglobin absorption changes in muscle have led to the development of a new approach using short pulses of light which permits the calculation of the path length for continuous light measurements of 2 cm for a particular geometry.
372 citations
TL;DR: In this article, a method for the measurement of spectral absorption coefficients, fluorescence excitation, and fluorescence yields for pigmented particles retained on filters was described. But the method was not applied to a study of photoadaptation in several phytoplankton species and revealed variations in the blue for chlorophyll α-specific absorption [αph*(λ)] and F *(λ) of greater than 3− and 10-fold.
312 citations
TL;DR: In this article, the authors show that the exciton-trapped carrier interaction is mainly responsible for the observed bleaching of the excitonic absorption, and the recovery time of the absorption bleaching is determined by the trapped carrier relaxation time, which is sensitive to fabrication methods and can be controlled by surface chemistry.
Abstract: We report a picosecond pump–probe study of 55 A cadmium sulfide microcrystallites embedded in polymer films. Large negative absorbance changes at wavelengths corresponding to energies near the band gap are observed. This absorption bleaching and the associated changes in refractive index are mainly responsible for the large nonlinearity observed in degenerate four‐wave mixing experiments. Based on photoluminescence data, the known electron‐trapping cross section of defects, and these pump–probe experiments, we show that the conventional carrier density‐dependent band‐filling mechanism cannot account for the data, and the absorption bleaching is due to the saturation of the excitonic transition. We further show that the phase‐space filling and exchange effects from exciton–exciton and exciton‐free carrier interactions fail to account for the observed data. Instead, we propose that the exciton‐trapped carrier interaction is mainly responsible for the observed bleaching of the excitonic absorption. This interaction is unique for small semiconductor clusters since the presence of a high density of defects (most likely on the surfaces) causes the extremely rapid trapping of free carriers. According to this model, the recovery time of the absorption bleaching is determined by the trapped‐carrier relaxation time, which is sensitive to the fabrication methods and can be controlled by surface chemistry. Our study also demonstrates that one needs to understand the effects of surfaces and control the surface chemistry before the important question of size effects on the nonlinear optical properties can be addressed.
216 citations
TL;DR: In this article, the authors present a detailed characterization of the output of optical limiters using photogenerated carrier defocusing within the material to limit the output fluence and irradiance.
Abstract: We present a detailed characterization of the output of passive semiconductor-based optical limiters. These devices utilize two-photon absorption along with photogenerated carrier defocusing within the material to limit the output fluence and irradiance. In addition to protecting downstream optical components, the focusing geometry combined with these nonlinearities makes the devices self-protecting. Such devices have a broad working wavelength range since both the initial two-photon absorption and the subsequent carrier refraction are slowly varying funtions of wavelength. For example, ZnSe should have a useful range of from 0.5 to 0.85 μm. In this material we have observed the onset of limiting at input powers as low as 80 W when using 10-nsec, 0.53 μm input pulses. At the same wavelength, when 30 psec pulses into a monolithic ZnSe limiter are used, limiting begins at ≃300 W or 10 nJ. We also monitored the output spatial energy distribution along with the temporal response at each position, using a 2-psec-resolution streak camera. We found that the output fluence along with the output irradiance is effectively limited below detector damage thresholds over an input range of 4 orders of magnitude. Additionally, since both two-photon absorption and the associated self-defocusing increase with decreasing band-gap energy, similar devices using narrow-gap semiconductors should have considerably lower limiting thresholds.
213 citations
TL;DR: In this paper, the authors present experimental data for BaTiO3 that exhibit an intensity dependence in the absorption coefficient and the two-beam coupling coefficient at intensities between 0.002 and 40 W/cm2.
Abstract: We present experimental data for BaTiO3 that exhibit an intensity dependence in the absorption coefficient and the two-beam coupling coefficient at intensities between 0.002 and 40 W/cm2. The effective empty-trap concentration was found to increase with intensity. We present a model, in the spirit of commonly used (photorefractive) theories, for photorefraction and optical absorption that explains these effects. The intensity dependence was attributed to the presence of secondary photorefractive centers.
205 citations
TL;DR: In this paper, a spectral model of irradiance is presented for the computation of light energy available at the surface and at various depths in the ocean for the wavelength range from 400 to 700 nm.
Abstract: A spectral model of irradiance is presented for the computation of light energy available at the surface and at various depths in the ocean for the wavelength range from 400 to 700 nm. For any latitude, irradiances are computed as a function of geographic location, date, and time. Application of the model is demonstrated through computation of the profiles of vertical attenuation coefficient and of the effective specific absorption of phytoplankton. The model results are compared with those from conventional procedures, which disregard spectral and angular distributions of the underwater light field, for calculation of the effective specific absorption. The magnitude of the errors incurred by such simplifications is estimated and is shown to be nonnegligible and variable with solar elevation, depth, and the phytoplank-on pigment concentration in the water.
199 citations
TL;DR: In this article, a detailed experimental study of coherent backscattering of light from aqueous suspensions of polystyrene microspheres is presented, focusing on the effects of particle size, of absorption due to added dye and of light polarization on the shape and height of the backscatter cone.
Abstract: A detailed experimental study of coherent backscattering of light from aqueous suspensions of polystyrene microspheres is presented. Emphasis is on the effects of particle size, of absorption due to added dye and of light polarization on the shape and height of the backscattering cone. For parallel polarization of incident and scattered beams, the scalar diffusion theory, parametrized by the transport mean free path l*, agrees well with our data up to surprizingly large scattering angles (ql * ~ 1) and quantitatively accounts for the rounding of the cones due to absorption. No deviations from the usual Gaussian statistics of scattered fields is observed up to λ/l* ∼ 0.1.
195 citations
TL;DR: In this article, the effect of local regions on solar p-mode oscillations was measured and measured in and around several sunspots, and it was found that active regions absorb an energy flux of the order of about 10 to 7th ergs/sq cm s, which is about 0.0001 of the sunspot energy deficit.
Abstract: The paper presents a technique for directly measuring the effect of local regions on solar p-mode oscillations. It was used to detect and measure p-mode absorption in and around several sunspots. Sunspots are found to absorb an energy flux of the order of about 10 to the 7th ergs/ sq cm s, which is about 0.0001 of the sunspot energy deficit. Thus, p-modes have only a negligible effect on the total sunspot energetics. However, the effect of active regions in dissipating high-degree p-mode energy appears to be very significant.
179 citations
TL;DR: In this article, the magnetic field induced microwave absorption in sintered high-Tc copper oxide superconductors is found to be proportional to the surface area of samples and not to their volume, establishing that absorption takes place near the sample surface.
Abstract: Magnetic-field-induced microwave absorption in sintered high-Tc copper oxide superconductors is found to be proportional to the surface area of samples and not to their volume, establishing that absorption takes place near the sample surface. The surface resistance and reactance increase with magnetic field as a result of energy loss through fluxons driven by superconducting currents. When the magnetic field is modulated, absorptive and dispersive signals arise from modulation of the complex surface impedance through processes induced by the changing magnetic fields.
TL;DR: In this article, a double layer structure of In-doped ZnO/ZnO has been constructed, which results in a large haze factor ( ∼16% ) at a wavelength of 0.7 μm.
Patent•
11 Apr 1988
TL;DR: A reflection type oximeter as mentioned in this paper comprises light emitting diodes (11 to 16) as first to sixth light sources which emit first and second beams of a wavelength involving a change in absorption due to a change an oxygen saturation of hemoglobin in blood of a tissue of a living body, third and fourth beams of another wavelength involving no change in absorbing power, and fifth and sixth beams of an additional wavelength involving relatively small change in absorbed power due to changes in a quantity of oxygen saturation.
Abstract: A reflection type oximeter comprises light emitting diodes (11 to 16) as first to sixth light sources which emit first and second beams of a wavelength involving a change in absorption due to a change an oxygen saturation of hemoglobin in blood of a tissue of a living body, third and fourth beams of another wavelength involving no change in absorption, and fifth and sixth beams of a further wavelength involving a relatively small change in absorption due to changes in a quantity of hemoglobin an oxygen saturation. The beams ae applied to the body tissue and the beams of the first to sixth light sources reflected by the body are received by a light receiving element (17). Intensities of the beams emitted from the light emitting diodes are set to predetermined levels and the intensities of the beams received by the light receiving element are evaluated by a CPU (23). Based on a predetermined function, the quantity of hemoglobin and of the oxygen saturation of the body tissue are evaluated. The resulting values are displayed on a display portion (26) and printed by a printer (27).
TL;DR: In this article, a many-body calculation of the electron-hole correlation enhancement is presented, which identifies this peak with the Mahan exciton, the result of the Coulomb interaction between the photoexcited hole in the valence band and the sea of electrons in the conduction band.
Abstract: The temperature-dependent optical absorption and luminescence spectra of GaAs/AlGaAs and InGaAs/InAlAs n-doped modulation-doped quantum wells is discussed with emphasis on the peak seen at the edge of the absorption spectra of these samples A many-body calculation of the electron-hole correlation enhancement is presented, which identifies this peak with the Mahan exciton-the result of the Coulomb interaction between the photoexcited hole in the valence band and the sea of electrons in the conduction band This calculation accounts for the strong dependence of the absorption edge peak on both the temperature and carrier concentration, in good qualitative agreement with experimental data and with previously published results The changes induced by the carriers on the subband structure through self-consistent calculations are also analyzed, and it is concluded that in these symmetric structures, the changes are small for achievable carrier densities >
TL;DR: In this paper, a detailed theortical study of the photodissociation of H2O and D2O in the first absorption band (λ∼165 nm) is presented.
Abstract: We report a detailed theortical study of the photodissociation of H2O and D2O in the first absorption band (λ∼165 nm). The calculations are three dimensional and purely quantum mechanical. They include an ab initio potential energy surface for the A state and a calculated SCF dipole moment function for the X→A transition. The dynamical calculations are performed within the infinite‐order‐sudden approximation for the rotational degree of freedom of OH and the LHL approximation for the masses. The resulting vibrational–translational motion is then treated exactly in two dimensions using hyperspherical coordinates. This study does not include any adjustable parameters. The thermally averaged total absorption spectra for H2O and D2O agree perfectly with the experimental spectra. Even finer details such as the progression of ‘‘vibrational’’ structures are well reproduced. They are not induced by any selective absorption but can be explained on the basis of the A state potential energy surface and details o...
TL;DR: In this article, the effect of laser-induced excitation on the luminescence and transient optical absorption induced by irradiation of crystalline SiO2 with an electron pulse have been studied.
Abstract: Linear polarisation, with respect to the z axis, and the effect of the subsequent laser-induced excitation on the luminescence and transient optical absorption induced by irradiation of crystalline SiO2 with an electron pulse have been studied. It is found that the luminescence spectrum consists of two bands peaked at 2.8 eV and at 2.5 eV and that the transition dipole moment of the former, which has been shown to be intrinsic, is nearly parallel to the z axis, while that of the latter is parallel to the x axis. In addition to the 5.2 eV transient optical absorption band, a satellite band at 4.2 eV is found to be induced by irradiation with an electron pulse. For both of these bands, the transition dipoles are found not to be parallel to any of the crystalline axes. Subsequent irradiation with a 4.0 or 5.6 eV laser pulse of a specimen irradiated with an electron pulse is found to eliminate both of these transient optical absorption bands and the 2.8 eV luminescence band. In view of previous work on optically detected magnetic resonance and volume changes induced by electron pulse irradiation, it is concluded that the 5.2 and 4.2 eV transient optical absorption bands and the 2.8 eV luminescence band are associated with self-trapped excitons. The existing models of self-trapped excitons are discussed on the basis of the present experimental results.
TL;DR: It is shown that the host glass influences the excited-state absorption spectra and that P(2)O(5)- or A1(2]O(3)-codoped fibers are the preferred choice for 514.5-, 655-, or 807-nm pump wavelengths owing to reduced pump excited- state absorption.
Abstract: Ground-state and excited-state absorption spectra covering the wavelength range of 450–1050 nm are presented for erbium-doped silica fibers with four different core codopants: GeO2, GeO2/B2O3, GeO2/P2O5, and Al2O3. It is shown that the host glass influences the excited-state absorption spectra and that P2O5- or Al2O3-codoped fibers are the preferred choice for 514.5-, 655-, or 807-nm pump wavelengths owing to reduced pump excited-state absorption. However, excited-state absorption is still significant at the 807-nm wavelength. Pump wavelengths of 524, 532, and 980 nm appear ideal because of the strong ground-state absorption and lack of excited-state absorption.
TL;DR: In this article, the experimentally determined energy levels of approximately 500 neutral and ionic transient molecules possessing from 3 to 6 atoms are tabulated together with the associated vibrational structure, the radiative lifetime, the principal rotational constants, and references to the pertinent literature.
Abstract: The experimentally determined eletronic energy levels of approximately 500 neutral and ionic transient molecules possessing from 3 to 6 atoms are tabulated together with the associated vibrational structure, the radiative lifetime, the principal rotational constants, and references to the pertinent literature. Vibrational and molecular beams, and in rare‐gas and nitrogen matrices are included. The types of measurement surveyed include conventional and laser‐ based absorption and emission techniques, laser absorption with mass analysis, and ultraviolet photoelectron spectroscopy.
TL;DR: The probability of internal reflection is calculated more accurately, and the effect on absorption of the decrease of the relative refractive index (liquid to material instead of air to material) is estimated, which decreases the albedo of the wetted surface.
Abstract: Angstrom has proposed that rough absorbing materials are darker when wet because their diffuse reflection makes possible total internal reflection in the water film covering them, increasing the likelihood of the absorption of light by the surface His model is extended here in two ways: the probability of internal reflection is calculated more accurately, and the effect on absorption of the decrease of the relative refractive index (liquid to material instead of air to material) is estimated Both extensions decrease the albedo of the wetted surface, bringing the model into good agreement with experiment
01 Jan 1988
TL;DR: This paper presents a probabilistic procedure for estimating the intensity and direction of radiolysis of Na6(CO3)(SO4)(SO3) in response to the proton-proton exchange between Na2SO4 and Na2CO3 .
Abstract: TIlEORy 5 1 Absorption . . . . . . . . . . . . .... 52 Scattering . ... ....... . . . . . . .. . .. ... 52 TRANSPARENCY ... . .. . . . . . . . . ...... . . . . . .. . . . . . . . .. . . . . .. . ..... 57 Membrane Scattering . . . . .. ....... 58 Cytoplasm Scattering and Transparency . . . . ....... 58 Protein-Protein Interactions: rt.-Crystallins ... . . . . ....... . . ....... ... . . . . . . . . .. . .. . 60 Calculating Transmitted Light From Interparticle Interactions . . . .. .. . .... ........ ....... . . . ... 6 1 OPACITIES AND CATARACT MODEL SySTEMS 62 The Two Lens-Scattering Systems . . . . . . .. . ..... . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. . . 62 Protein-Associated Opacities: Cold Cataracts and Calcium-Induced Opacification ... 64 Protein-Protein Interactions: y-Crystallins . . . . . . . . . 65 DiSCUSSION . . . . . . . . . . . . . ...... . . . . .. . . . . . . . . . . . . . . . . . ..... . . . . . . . .... 66
Proceedings Article•
IBM1
TL;DR: In this article, the violet at 380 nm has been achieved at temperatures near 20 K up to 12mW power with pump powers of several hundred milliwatts from two cw dye lasers and conservative 1 % output coupling.
Abstract: Continuous-wave laser operation in the violet at 380 nm has been achieved on the 4D3/2 → 4/11//2 transition in LaF3:Nd3+ at temperatures of <90 K. Two different upconversion pumping mechanisms resulted in laser action: (a) sequential two-step absorption of an IR (790-nm) photon and a yellow (590-nm) photon by the Nd3+ ions; (b) cooperative energy transfer upconversion following the absorption of one yellow (578-nm) photon per Nd3+ ion. At temperatures near 20 K up to 12-mW power at 380 nm was obtained using pump powers of several hundred milliwatts from two cw dye lasers and conservative 1 % output coupling. At 77 K, the output power decreased to ~4 mW.
TL;DR: This model provides an accurate means of interpolating and extrapolating the measurements to give a comprehensive characterization of intrinsic absorption properties with frequency and temperature (in the multiphonon region).
Abstract: Experimental characterization of the bulk absorption properties of sapphire, spinel, yttria, and ALON as a function of temperature is accomplished using a Bomem DA3.02 vacuum Fourier transform spectrometer and a heated cell. The measurements are performed between 2 and 20 μm from room temperatures to 775 K. Spectra of two samples of different thicknesses are ratioed to reduce surface effects and to provide a direct measure of the bulk extinction coefficient. Absorption coefficient and reflectivity data are used to determine parameters in a multiphoton absorption model. The model has proved valid up to the melting temperature of the material. This model provides an accurate means of interpolating and extrapolating the measurements to give a comprehensive characterization of intrinsic absorption properties with frequency and temperature (in the multiphonon region).
TL;DR: In this article, the authors present a simple computer model for the electric field dependence of the absorption of semiconductor multiple-quantum-well (MQW) structure that will be used to optimize the performance of MQW modulators.
Abstract: The authors present a simple computer model for the electric field dependence of the absorption of semiconductor multiple-quantum-well (MQW) structure that will be used to optimize the performance of MQW modulators. This model has been compared to absorption spectra derived from photocurrent measurements on a GaAs/(GaAl)As MQW p-i-n diode and it has been found that the well-established Stark shifts of the exciton and subband continua energies are significantly overestimated. This might be linked to uncertainty in knowing the electric fields over the wells; and if a drop of 1.4 V somewhere in the device is assumed, a much better match can be achieved between the theoretical and experimental shifts. Given this improved match in the shifts the reduction in the oscillator strengths and the broadening are modeled very well. It is concluded that the model is likely to prove a useful tool for optimizing electroabsorption modulator design. >
TL;DR: In this article, the forward electron transfer in intact photosystem I particles from Synechococcus sp. at room temperature has been studied by flash absorption spectroscopy with a time resolution of 5 ns.
TL;DR: In this article, a temperature dependence of the absorption cross-section (sigma) of NO2 in the visible-ultraviolet region was made in order to provide a more reliable data base for the calculation of NO 2 photolysis rates in the atmosphere.
Abstract: A redetermination of the temperature dependence of the absorption cross-section (sigma) of NO2 in the visible-ultraviolet region was made in order to provide a more reliable data base for the calculation of NO2 photolysis rates in the atmosphere. Experiments over a wide range of temperatures and NO2 concentrations were conducted. The integral of a plot of sigma versus the inverse of the wavelength was essentially independent of temperature. Increasing temperature produced a shift of the spectrum toward longer wavelengths, resulting in a small negative temperature dependence of sigma over the 264-400 nm range and a small positive dependence over the 450-649 nm range. Increasing temperature produced broadening of individual spectral features, resulting in a systematic lowering of peaks and filling of valleys. Recommended cross sections are presented for use in tropospheric NO2 photolysis rate calculations.
TL;DR: In this paper, the effect of photo-electron emission on CdS particles in aqueous solutions was studied at various laser intensities. And the following conclusions were drawn: (1) the specific rate of recombination of charge carriers increases in high intensities; (2) positive holes cannot be accumulated on the colloidal particles; (3) photoelectron emissions is a process in which two photons are involved.
Abstract: Laser illumination of small CdS particles in aqueous solution leads to the formation of hydrated electrons, which are detected by their strong absorption. The yield increases with decreasing particle size. The maximum quantum yield observed is 0.07 electrons emitted per photon absorbed. At the highest laser intensities applied, five electrons are emitted from one colloidal particle. The absorption of the remaining holes is also observed. The emitted electrons react with colloidal particles in solution. During the laser flash a strong bleaching signal, attributed to the electrons generated in the particles, is recorded shortly below the onset of absorption. With knowledge of the specific absorbance, the stationary concentration of electrons on the particles during the laser flash is calculated. These effects are studied at various laser intensities. The following conclusions are drawn: (1) the specific rate of recombination of charge carriers increases in high intensities; (2) positive holes cannot be accumulated on the colloidal particles; (3) photoelectron emission is a process in which two photons are involved. They create two excited states (electron-hole pairs), the subsequent interaction between which results in electron emission.
TL;DR: A systematic comprehensive consideration of the emission spectroscopy, emission lifetimes, transient spectroscopic, as well as quantum yields of fluorescence, triplet occupation and photoisomeriz‐ation is given for a wide variety of polyene derivatives including retinyl and longer, aswell as shorter chainlength homologs.
Abstract: — A systematic comprehensive consideration of the emission spectroscopy, emission lifetimes, transient spectroscopy, as well as quantum yields of fluorescence, triplet occupation and photoisomeriz-ation is given for a wide variety of polyene derivatives including retinyl and longer, as well as shorter chainlength homologs. Absorption spectral properties and the results and significance of theoretical calculations are also included. Chainlength, solvent and temperature effects on state order and photophysical as well as photoisomerization properties are evaluated. The mechanism for the primary light step in vision is considered in light of photophysical and photoisomerization data on model visual pigments and rhodopsin.
TL;DR: In this paper, the absorption spectra of BrO in the wavelength range 312-385 nm were measured at 298±2 and 223±4 K using a flow tube reactor coupled to a diode array spectrometer.
TL;DR: In this article, the authors solve the radiation transport problem in a dusty medium with one-dimensional planar, spherical or cylindrical geometry, and determine selfconsistently the effects of multiple scattering, absorption, and re-emission of photons on the temperature of dust grains and the characteristics of the internal radiation field.
TL;DR: Surface emission profiles and related functions are computed for particles (photons) migrating within a semiinfinite medium containing a surface layer whose absorbance differs from that of the underlying layer.
Abstract: Surface emission profiles and related functions are computed for particles (photons) migrating within a semiinfinite medium containing a surface layer whose absorbance differs from that of the underlying layer Photons are assumed to be inserted at a single point on the surface In certain cases distinct features appear in the emission profiles which enable determination of the thickness of the top layer and of the absorption coefficients of both layers Computations are performed to provide estimates of parameter ranges for which the presence of one layer distorts photon emission profiles from the other Several ancillary functions are calculated, including the absorbance profile as a function of depth, the expected path length of photons that are reemitted at a distance rho from the point of insertion, and the average depth probed by those reemitted photons