Changes In Absorption Coefficient Research Articles

Intersubband optical absorption coefficients and refractive index changes in a V‐groove quantum wire

AbstractIn this paper, the intersubband optical absorption coefficients and the refractive index changes are studied in a V‐groove quantum wire. We use analytical expressions for these properties obtained by the compact‐density matrix formalism. In this regard, the linear, nonlinear and total intersubband absorption coefficients and refractive index changes are investigated as a function of the bend width wire (b), the incident optical intensity (I), and the angle θ. According to the results obtained from the present work, it is deduced that: (i) The linear terms in the refractive index changes and absorption coefficients dose not change with incident optical intensity whereas nonlinear terms depend on incident optical intensity; (ii) The total refractive index changes and the absorption coefficients reduce as the incident optical intensity increases; (iii) The total absorption coefficient and refractive index changes increase and also shift toward higher energies as the bend width wire increases; and (iv) The total refractive index changes and absorption coefficients shift toward higher energies as the angle θ increases.

Intersubband optical absorption coefficient changes and refractive index changes in a two-dimensional quantum pseudodot system

The optical absorption coefficient changes and refractive index changes associated with intersubband transitions in a two-dimensional quantum pseudodot system under the influence of a uniform magnetic field are theoretically investigated. In this regard, the electronic structure of the pseudodot system is studied using the one-band effective mass theory, and by means of the compact density matrix approach linear and nonlinear optical absorption coefficient and refractive index changes are calculated. The effects of an external magnetic field and the geometrical size of the pseudodot system on the optical absorption coefficient and refractive index changes are investigated. It is found that the absorption coefficient and refractive index changes are strongly affected not only by an external magnetic field but also by the geometrical size of the pseudodot system.

Ocean acidification and its impact on ocean noise: Phenomenology and analysis

Ocean acidification has been observed since the beginning of the industrial era and is expected to further reduce ocean pH in the future. A significant increase in ocean noise has been suggested based upon the percentage change in acoustic absorption coefficient at low frequencies. Presented here is an analysis using transmission loss models of all relevant loss mechanisms for three environments experiencing a significant near-surface pH reduction of 8.1-7.4. Results show no observable change in the shallow water and surface duct environments, and a statistically insignificant change of less than 0.5 dB for all frequencies in the deep water environment.

Conformational and thermodynamic characterization of the premolten globule state occurring during unfolding of the molten globule state of cytochrome c

It has already been shown that the mutant Leu94Gly of horse cytochrome c exists in a molten globule (MG) state. We have carried out studies of reversible folding and unfolding induced by LiCl of this mutant at pH 6.0 and 25 °C by observing changes in the difference molar absorption coefficient at 402 nm, the mean residue ellipticity at 222 nm, and the difference mean residue ellipticity at 409 nm. This process is a three-state process when measured by these probes. The stable folding intermediate state has been characterized by far- and near-UV circular dichroism, tryptophan fluorescence, 8-anilino-1-naphthalenesulfonic acid binding, and dynamic light scattering measurements, which led us to conclude that the intermediate is a premolten globule (PMG). Analysis of the reversible unfolding transition curves for the stability of different states in terms of the Gibbs free energy change at pH 6.0 and 25 °C led us to conclude that the MG state is more stable than the PMG state by 5.4 ± 0.1 kcal mol(-1), whereas the PMG state is more stable than the denatured (D) state by only 1.1 ± 0.1 kcal mol(-1). A comparison of the conformational and thermodynamic properties of the LiCl-induced PMG state at pH 6.0 with those of the PMG state induced by NaCl at pH 2.0 suggests that a similar PMG state is obtained under both denaturing conditions. Differential scanning calorimetry measurements suggest that heat induces a reversible two-state transition between MG and D states.

Plasma photonic devices with complex refractive index in EUV region

We report two types of plasma photonic devices using complex refractive index around an absorption edge. Cherenkov radiation using laser-produced electron beam having a Maxellian distribution is evaluated by theoretical calculation. In the calculation result, this Cherenkov radiation is monochromatic in spite of energy distribution. This monochromaticity is due to characteristic of real part of complex refractive index around an absorption edge. Nonlinear transmission in metal using EUV light pulse is also reported. Transmission becomes nonlinearly higher with increase in energy density of EUV light from 6 J/cm2. This nonlinear phenomenon is caused by change of absorption coefficient, that is, imaginary part of complex refractive index.

Nonlinear optical properties of a hydrogenic impurity in an ellipsoidal finite potential quantum dot

The linear and the third-order nonlinear optical absorption coefficient and refractive index changes of a hydrogenic impurity in an ellipsoidal quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of the size and geometry of the dot, aluminium concentration in GaAs/ Al xGa 1− x As structures, and optical intensity on the optical absorption coefficient and refractive index changes are investigated. It is found that the light intensity, size and geometry of the dot and aluminium concentration have a great influence on the absorption coefficient and refractive index changes of the dot.

Diffusion of Methylene Blue in Phantoms of Agar Using a Photoacoustic Technique

In this work, the kinetics of diffusion of methylene blue in agar aqueous solution is studied using a photoacoustic technique. Two agar phantoms solutions in water with a relation of mass/volume of 0.01% and 0.05% were analyzed. The study was performed using a modified Rosencwaig photoacoustic cell that is enclosed by transparent windows, on both sides. The sample is deposited directly on top of the upper window. A red light beam, at a fixed modulation frequency, is sent through the lower window illuminating the sample and inducing the photoacoustic effect inside the closed chamber of the cell. At the beginning of the experiment, a droplet of 100μL of agar solution is deposited; afterwards, the signal stabilizes, and 10μL of methylene blue aqueous solution (0.0125 g · mL−1) is added to the surface of the agar. During the first seconds of the experiment, the photoacoustic signal amplitude increases followed by a gradual and long decay. Results for modulation frequencies in the range from 10Hz to 80Hz for both agar concentrations are presented. A simple theoretical approach is presented to analyze the experimental data. It is demonstrated that the kinetics of the process can be parameterized as a function of the changes of an effective optical absorption coefficient. From these results, the characteristic time, in which the dye diffusion process stabilizes, is obtained. It is found that this time is larger for samples with a higher agar concentration. These differences provide important results for biomedical sciences in which agar gels are used as phantoms resembling some of the properties of living organs and tissues.

INTERSUBBAND OPTICAL ABSORPTION COEFFICIENTS AND REFRACTIVE INDEX CHANGES OF AN ELLIPSOIDAL FINITE POTENTIAL QUANTUM DOT

Intersubband optical absorption coefficient and refractive index changes of a weakly prolate ellipsoidal quantum dot, using the compact-density matrix formalism and iterative method, are investigated. In this regard, the linear and nonlinear intersubband optical absorption coefficient and refractive index changes of a GaAs / Al x Ga 1-x As ellipsoidal quantum dot, as functions of the dot radius, ellipticity constant, stoichiometric ratio and incident light intensity are calculated. The results indicate that absorption coefficient and refractive index changes strongly depend on the light intensity, size and geometry of the dot and structure parameters such as aluminium concentration in GaAs / Al x Ga 1-x As structures.

Improving the accuracy of sound absorption measurements.

Sound absorption test methods, such as ASTM C423, provide criteria for test chamber qualification. Measurements required during the ASTM C423 qualification process examine the variation in decay rates with microphone and test specimen locations. In addition, it is recommended to measure the change in sound absorption coefficients of a reference specimen with various amounts of diffusion in the room. However, there is little published information regarding systematic methods for determining diffuser, microphone, or specimen locations; therefore, qualification or improvement to the reverberation room depends on the acoustician’s best judgment. As part of a continual improvement process to reduce testing variation, a mapping technique was utilized to visualize the three dimensional sound field in the room and determine changes necessary to improve the diffusion and repeatability of sound absorption measurements.

Temperature-dependent optical properties of Intralipid® measured with frequency-domain photon-migration spectroscopy

We present the temperature dependence of absorption and reduced scattering coefficients of 1.8% Intralipid measured by frequency-domain photon-migration spectroscopy between 710 and 850 nm. These measurements were made in the physiologically relevant 30 to 40 degrees C temperature range. The temperature coefficients for absorption were consistent during heating and cooling and follow closely other reported results. The change in absorption coefficient at 740 nm suggests that a minimum temperature change of 4 degrees C is observable within the error limits. We found that the reduced scattering coefficient shows a hysteresis with temperature at 740 nm. The temperature coefficient for reduced scattering determined from heating cycle measurements agrees with theory and other measurements within the error limits.

Optical transmission of PMMA optical fibres exposed to high intensity UVA and visible blue light

Optical transmission of PMMA (polymethylmethacrylate) POF (polymer optical fibre) in the spectral range from 280 to 450 nm is investigated with a high radiation emission source comprising a mercury lamp delivering 40 W/cm 2 at the PMMA POF launch face. The heat generated from the radiation source causes a sudden drop in the launched radiation due to thermal-oxidation and photo-degradation of the launch face of the PMMA POF; this results in a loss of 53% of the total launched power within 13 min of exposure to the source. The thermal-oxidation degradation is controlled by a cooling device which improves the transmission stability of the fibre. However, photo-degradation is still active and causes a loss in power of 7% in 13 min. The spectral output of the transmitted radiation through the PMMA POF was monitored and indicates the variation in optical loss with wavelength. High rates of nominal absorption for the irradiated PMMA POF are found below 320 nm wavelength. From the Beer–Lambert law, the photo-degradation effect with time of a fixed path length of PMMA POF is described by the absorption coefficient ( α λ , cm −1) . The nominal absorption coefficient α λ values in the range 335–368 nm wavelength are found to be higher after 1 h of irradiation than the values in the range 406–438 nm. However, the relative change in the nominal absorption coefficient Δ α λ is greater at 438 nm than at 335 nm, 368 or 406 nm. After 1 h of irradiation with the cooling device in place, the PMMA POF transmission was reduced to 44.8% of its initial value; this recovered to a maximum of 86% of the original transmission of the total launched power after 5 weeks in ambient conditions.

Nonlinear optical properties of a two-dimensional elliptic quantum dot

The linear and third order nonlinear optical absorption coefficient and refractive index changes of an elliptic quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of optical intensity, size and geometry of the dot on the optical absorption coefficient and refractive index changes are investigated. It is found that, not only the light intensity but also the size and the geometry of the dot have a great influence on the optical absorption coefficient and refractive index changes of the system.

Intersubband optical absorption coefficients and refractive index changes in a parabolic cylinder quantum dot

Optical absorption coefficients and refractive index changes associated with intersubband transition in a parabolic cylinder quantum dot are theoretically investigated. In this regard, the electronic structure of the dot is studied using the one band effective mass theory, and by means of the compact-density matrix approach the linear and nonlinear optical absorption coefficients and refractive index changes are calculated. The effects of the size of the dot, optical intensity and electromagnetic field polarization on the optical absorption coefficient and refractive index changes are investigated. It is found that absorption and refractive index changes are strongly affected not only by the size of the dot but also by optical intensity and the electromagnetic field polarization.

In situ pump probe optical absorption studies on Sb/As 2S 3 nanomultilayered film

We report the in situ optical transmission change in the complete visible region of the electromagnetic spectrum to asses the kinetics of photo induced interdiffusion in Sb/As 2S 3 nanomultilayered film. The interdiffusion of Sb into As 2S 3 matrix results in the formation of Sb–As 2S 3 ternary solid solutions which is explained by the change in optical band gap, absorption coefficients and Tauc parameter ( B 1/2) with evolution of time. The wavelength dependence of the time constants provides a better description of photo induced effects. The time evolution of the absorption coefficients and optical band gap are significantly faster in this process.

Hydrogen Bonding in Polymers: Effect of Temperature on the OH Stretching Bands of Poly(vinylphenol)

A detailed analysis of the bands appearing in the OH stretching region of the infrared spectrum of poly(vinylphenol) and their changes with temperature is presented. Bands usually assigned to “free” (non-hydrogen-bonded) groups contain overlapping contributions from both monomeric and end-group species, both hydrogen-bonded to π orbitals. Assignments of bands due to hydrogen-bonded groups are made on the basis of whether the proton and oxygen in a particular OH group are both involved in hydrogen bonds (as “donors” and “acceptors”, respectively) or whether one or the other is “free” (not hydrogen-bonded). The assignment of other modes is more uncertain, and various possibilities are discussed. Changes in absorption coefficient with temperature appear to affect bands due to hydrogen-bonded groups in the interior of chains and monomeric species by essentially the same amount. The large change in absorption coefficient of the hydrogen-bonded band relative to a band assigned to free groups postulated in a pre...

Kinetics of photodarkening in a-As2Se3 thin films

We report kinetics of photodarkening of a-As2Se3 films in terms of changes in absorption coefficient and optical band gap. These are estimated by in situ measurements of transmission spectra at intervals of 10 ms under laser illumination. The absorption coefficient increase with increasing time of laser illumination before saturating. The change in optical band gap, estimated from transmission spectra are studied as a function of time and intensity. A theoretical fitting of the change in optical parameters is done using photon-assisted site switching model, yielding the time constants for the changes in optical absorption and optical band gap. The change in absorption coefficient and optical band gap with incident laser intensity is also examined to investigate the saturation phenomenon.

CO2 gas resonance absorption at CO2 laser wavelength in multiple laser coating

Multiple laser beams demonstrate many advan- tages as energy sources in diamond synthesis. In a reported amazingly-fast multiple laser coating technique, CO2 gas is claimed as the sole precursor or secondary precursor for forming a diamond or diamond-like carbon, which remains poorly understood. The absorption coefficient changes un- der the irradiation of multiple lasers are one of the keys to resolve the mysteries of multiple laser beam coating processes. This study investigates the optical absorption in CO2 gas at the CO2 laser wavelength. The resonance ab- sorption process is modeled as an inverse process of the lasing transitions of CO2 lasers. The well-established CO2 vibrational-rotational energy structures are used as the ba- sis for the calculations with the Boltzmann distribution for equilibrium states and the three-temperature model for non- equilibrium states. Based on the population distribution, our predictions of the CO2 absorption coefficient changes as a function of temperature are in agreement with the published data.

Intersubband absorption modulation in coupled double quantum wells by external bias

The scope for using intersubband absorption for electroabsorption modulation has been investigated by a detailed self-consistent solution of the coupled Schrödinger–Poisson equations. Rapid changes in intersubband absorption coefficient with electric field are predicted for modulation-doped In0.53Ga0.47As/AlAs deep coupled quantum wells arising from a combination of Stark effect, field-induced changes in the optical matrix elements and quantum well occupancy. Extensive simulations reveal that controlling the density of electrons in the quantum wells is potentially the most robust process for prospective high-speed modulation by intersubband electroabsorption.

Responses of Emiliania huxleyi (Prymnesiophyceae) to step changes in photon flux density

A non-calcifying strain (Ply 92) of Emiliania huxleyi (Lohman) Hay et Mohler, was subjected to reciprocal step changes of photon flux density (PFD) between 50 and 800 µmol photons m−2 s−1 to establish the timescales of photoacclimation. Photoacclimation in E. huxleyi involved adjustment of cellular light harvesting pigment contents, but not cellular ribulose bisphosphate carboxylase-oxygenase (RuBisCO) or cellular RNA contents. There was considerable variability in both the magnitude and the rate of the response of physiological and biophysical variables to the step changes in PFD. The slowest response was observed in cellular chl a content, and the chl a/carbon ratio. Acclimation of these variables appeared to be due to dilution of pigment pools rather than to pigment turnover. Changes in the chl a-specific light absorption coefficient accompanied changes in cellular chl a content. Following the shifts in PFD, the efficiency of excitation energy transfer from the photosystem II antennae to reaction centres II (RCII), as assessed from , adjusted within 12 h. The efficiency of charge separation within RCII, as assessed from , adjusted on a similar timescale. The overall efficiency of photosystem II (PSII), as assessed from / , showed a step response to the change of PFD due to inverse changes in , and . Changes in non-photochemical excitation energy quenching were correlated with the relative and absolute abundance of the xanthophyll cycle pigments diadinoxanthin and diatoxanthin, which appeared to be reversibly interconverted with fucoxanthin. Thus, acclimation to PFD involved co-ordinated adjustment of the quantum efficiency of RCII, the efficiency of excitation energy transfer from the light-harvesting pigment bed to RCII, and cellular light absorption on overlapping time scales.

Monte Carlo study of global interference cancellation by multidistance measurement of near-infrared spectroscopy

The performance of near-infrared spectroscopy is sometimes degraded by the systemic physiological interference in the extracerebral layer. There is some systemic interference, which is highly correlated with the functional response evoked by a task execution. This kind of interference is difficult to remove by using ordinary techniques. A multidistance measurement method is one of the possible solutions for this problem. The multidistance measurement method requires estimation parameters derived from partial pathlength values of tissue layers to calculate an absorption coefficient change from a temporal absorbance change. Because partial path lengths are difficult to obtain, experimentally, we estimated them by a Monte Carlo simulation based on a five-layered slab model of a human adult head. Model parameters such as thickness and the transport scattering coefficient of each layer depend on a subject and a measurement position; thus, we assumed that these parameters obey normal distributions around standard parameter values. We determined the estimation parameters that provide a good separation performance in average for the model parameter distribution. The obtained weighting is robust to model parameter deviation and provides smaller errors on average compared to the parameters, which are determined without considering parameter distribution.