Relative Absorption Strength Research Articles

Wavelength and polarisation dependence of pump-induced loss in Ti:sapphire

We use pump beam wavelength and polarisation to demonstrate that the phenomenon of pump-induced loss in Ti:sapphire is linked to simultaneous excitation of two separate absorption bands: the Ti3+ pump band and the parasitic 400 nm residual absorption. We find that the degree of pump-induced loss is linked to the relative absorption strengths of the residual absorption band and the Ti3+ pump band at the wavelength(s) of excitation.

Ammonia-methane ratios from H-band near-infrared spectra of late-T and Y dwarfs

Aims. Our goals are to investigate the relative absorption strengths of ammonia and methane using low-resolution H-band (1.5−1.7 microns) spectra obtained in the laboratory and compared with observational spectra of late-T and Y dwarfs, and to estimate what can be expected from the wide-angle low-resolution near-infrared spectroscopic survey that will be provided by the upcoming Euclid space mission. Methods. Gas cells containing ammonia and methane at atmospheric pressure were custom-made in our chemical laboratory. Low-resolution near-infrared spectroscopy of these gas cells was collected in our optical laboratory. It is compared with simulated spectra using the high-resolution transmission molecular absorption database (HITRAN) for temperatures of 300 K and 500 K, and with near-infrared spectra of late-T dwarfs, Y dwarfs, Jupiter, and Saturn. We selected for this investigation the spectral region between 1.5 and 1.7 microns (H band) because it is covered by the Euclid red grism, it is particularly sensitive to the relative proportions of ammonia and methane opacity, and it is free from strong contributions of other abundant molecules, such as water vapor. Results. The laboratory spectra showed that the ammonia and methane features present in the simulations that used the HITRAN database are incomplete. Using our laboratory spectra, we propose a modified version of the NH3-H spectral ratio with expanded integration limits that increases the amplitude of variation in the index with respect to spectral type. Combinations of our laboratory spectra were used to find the best fits to the observed spectra with the relative absorption ratio of ammonia to methane as a free parameter. A relationship was found between the Teff and the ratio of ammonia to methane from spectral classes T5 to Y2 (1100 K–350 K), in fairly good qualitative agreement with theoretical predictions for high-gravity objects and temperatures from 1100 K to 500 K. The ammonia-to-methane ratios in late-T and Y dwarfs are similar to that of Jupiter, suggesting a similar chemical composition. Simulations of the spectroscopic performance of Euclid suggest that it will yield Teff values and ratios of ammonia to methane for over 103 late-T dwarfs in the entire wide survey.

Investigation of excitation interference in laser-induced breakdown spectroscopy assisted with laser-induced fluorescence for chromium determination in low-alloy steels

Chromium determination in steels suffered from excitation interference in laser-induced breakdown spectroscopy assisted with laser-induced fluorescence (LIBS-LIF). In this work, excitation interference between target chromium atoms and matrix iron atoms was investigated in detail. Relative absorption strength (RAS) of chromium and iron was mathematically deduced and utilized to estimate the excitation interference theoretically. Standard calibration curves of LIBS and LIBS-LIF for chromium determination in low-alloy steels were experimentally established. The chromium line 359.35 nm with less interference in the RAS map provided better analytical performance (slope of 1.99×105 counts/ wt%, detection limit of 8.64 μg g−1, R2 of 0.992, average RSD of 2.89%), in accordance with the theoretical estimation. This work realized sensitive and accurate determination of trace chromium in low-alloy steels, even influenced by excitation interference. An effective estimation method was provided for evaluating excitation interference to choose a suitable excitation line.

Ferroelectric liquid crystal mixture dispersed with tin oxide nanoparticles: Study of morphology, thermal, dielectric and optical properties

The present study is dedicated to the use of tin oxide (SnO2) nanoparticles dispersed in a multicomponent ferroelectric liquid crystal (FLC) mixture with the aim of showing their effects on the textural, dielectric, thermal and optical properties. The influence of the dopant concentration on the various physical parameters of the FLC has been discussed. Formation of self assembled two dimensional arrays of nanoparticles has been observed in the planar aligned textures of composites which is oriented perpendicular to the rubbing direction. The Differential Scanning Calorimetry study confirms the change in phase transition temperature of all the composites. The relative permittivity, absorption strength and ac conductivity have been reduced in presence of the nanoparticles. The optical extinction of neat ferroelectric liquid crystal has been decreased after the addition of tin oxide nanoparticles. The quenching phenomenon was observed for nanoparticles dispersed ferroelectric liquid crystal.

Optical properties of donor–acceptor conjugated copolymers: A computational study

TDDFT calculations are associated to an extrapolation scheme to predict the optical properties of twelve donor-acceptor copolymers, in which carbazole, benzodithiophene or cyclopentadithiophene donor subunits are combined to benzofurazane, benzothiadiazole or diketopyrrolopyrrole acceptor moieties. Relative excitation energies and absorption strengths are rationalized in terms of geometrical, electronic and optical descriptors. It is shown that the combination of a cyclopentadithiophene with a diketopyrrolopyrrole leads to the lowest excitation energy and highest light absorption efficiency within the series. However, combining cyclopentadithiophene and benzodithiophene subunits appears as more efficient for solar cell applications due to better energy level alignment with respect to PCBM.

Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices.

Optimization of thin film photovoltaics (PV) relies on characterizing the optoelectronic and structural properties of each layer and correlating these properties with device performance. Growth evolution diagrams have been used to guide production of materials with good optoelectronic properties in the full hydrogenated amorphous silicon (a-Si:H) PV device configuration. The nucleation and evolution of crystallites forming from the amorphous phase were studied using in situ near-infrared to ultraviolet spectroscopic ellipsometry during growth of films prepared as a function of hydrogen to reactive gas flow ratio R = [H2]/[SiH4]. In conjunction with higher photon energy measurements, the presence and relative absorption strength of silicon-hydrogen infrared modes were measured by infrared extended ellipsometry measurements to gain insight into chemical bonding. Structural and optical models have been developed for the back reflector (BR) structure consisting of sputtered undoped zinc oxide (ZnO) on top of silver (Ag) coated glass substrates. Characterization of the free-carrier absorption properties in Ag and the ZnO + Ag interface as well as phonon modes in ZnO were also studied by spectroscopic ellipsometry. Measurements ranging from 0.04 to 5 eV were used to extract layer thicknesses, composition, and optical response in the form of complex dielectric function spectra (ε = ε1 + iε2) for Ag, ZnO, the ZnO + Ag interface, and undoped a-Si:H layer in a substrate n-i-p a-Si:H based PV device structure.

On the relative absorption strengths of water vapour in the blue wavelength range

Abstract. In recent updates of the HITRAN water vapour H2O spectroscopic compilation covering the blue spectral region (here: 394–480 nm) significant changes for the absorption bands at 416 and 426 nm were reported. In order to investigate the consistency of the different cross-sections calculated from these compilations, H2O vapour column density ratios for different spectral intervals were retrieved from long-path and multi-axis differential optical absorption spectroscopy (DOAS) measurements. We observed a significant improvement of the DOAS evaluation when using the updated HITRAN water vapour absorption cross-sections for the calculation of the reference spectra. In particular the magnitudes of the residual spectra as well as the fit errors were reduced. However, we also found that the best match between measurement and model is reached when the absorption cross-section of groups of lines are scaled by factors ranging from 0.5 to 1.9, suggesting that the HITRAN water vapour absorption compilation still needs significant corrections. For this spectral region we present correction factors for HITRAN 2009, HITRAN 2012, HITEMP and BT2 derived from field measurements. Additionally, upper limits for water vapour absorption in the UV-A range from 330 to 390 nm are given.

Spectroscopic Characteristics of Three Dimensional Split-Ring Resonator Arrays at Terahertz Frequencies.

In this work, three-dimensional, stacked arrays of subwavelength, square, dual, concentric split ring resonators exhibiting characteristics at the Terahertz frequencies have been designed, simulated, and fabricated through a photolithographic lift-off process and electron beam evaporation metal deposition. Characterization of the split-ring resonator arrays was performed by transmission mode Terahertz time domain spectroscopy. The effects of the split-ring resonator unit cell spatial dimensions on resonant absorption frequencies and relative absorption strength are investigated as well as effects from the addition of a dielectric spacing layer and additional split-ring resonator layer. The split-ring resonator arrays were seen to develop two distinct and switchable LC resonances as well as a dipole resonance by measuring the arrays at 0° and 90° in-plane rotations about the terahertz propagation vector. The dielectric spacing layer served to effectively lower the resonant frequencies of the split-ring resonantors while the dual split-ring resonator array was seen to have a slight modulating effect on the absorption strength at the resonant frequencies compared to that of the passivated array without the second layer.

An analytical data inversion method for magnetic circular dichroism spectra dominated by the “B-term”

A simple procedure is developed enabling the analytical inversion of an (unpolarized) absorption spectrum combined with a Magnetic Circular Dichroism (MCD) spectrum to resolve two overlapping bands of orthogonal polarization. This method is appropriate when (i) the overlapping transitions are well isolated from other bands, and (ii) when their electronic spacing is large enough so that the "A-term" and "C-term" contributions to the MCD spectrum can be ignored and hence only the "B-term" contribution need be considered. We apply this procedure to assign the Q-band system of chlorophylls, though similar challenges also commonly arise throughout both conventional and X-ray MCD (XMCD) spectroscopy. Analytical data inversion has not previously been possible as the inversion process is two-fold underdetermined. We show that the assumptions of isolated spectra and "B-term" dominance yields one generally valid constraint, leaving only one quantity unspecified by the experimental data. For some systems, an approximation leading to equal but opposite sign B-term magnitudes of the two components may be reasonable, but for chlorophyllides we find this constraint to be inappropriate. Instead, we constrain a bounded variable controlling the relative absorption strengths. Derived spectral bandshapes of the individual components are shown to be insensitive to its particular value, allowing weak spectral components of one polarization overlapped by intense components of the other to be immediately exposed. This is demonstrated for the chlorophylls, molecules for which the failure to detect such weak features historically led to incorrect proposals for the Q-band assignments.

Probing Coster–Kronig Transitions in Aqueous Fe2+ Solution Using Inverse Partial and Partial Fluorescence Yield at the L-Edge

Specific Coster–Kronig (CK) transitions in 3d transition metals are close to the threshold of energetic possibility, being disallowed in free atoms, while possible in solids. Moreover, they have been shown to be quite sensitive to chemical bonding. Nevertheless, there has been no direct study of such behavior in solution. Here we present an approach to quantify such transitions in solution, by comparing relative fluorescence of different edges to their relative absorption strengths. The difficulties of acquiring a measurement of the absorption in solution are overcome by applying the recently developed method of inverse partial fluorescence yield to a liquid sample using the microjet. This method has been demonstrated on solids to be bulk sensitive and able to obtain absorption spectra free of self-absorption or saturation effects. We extend this approach to investigate the L-edge of aqueous Fe2+ using a combination of a soft X-ray light source and a high-resolution X-ray emission spectrometer.

Thermodynamic Efficiency Limit of Molecular Donor‐Acceptor Solar Cells and its Application to Diindenoperylene/C60‐Based Planar Heterojunction Devices

AbstractIn organic photovoltaic (PV) cells, the well‐established donor‐acceptor (D/A) concept enabling photo‐induced charge transfer between two partners with suitable energy level alignment has proven extremely successful. Nevertheless, the introduction of such a heterojunction is accompanied with additional energy losses as compared to an inorganic homojunction cell, owing to the presence of a charge‐transfer (CT) state at the D/A interface. Based on the principle of detailed balance, a modified Shockley‐Queisser theory is developed including the essential effects of interfacial CT states, that allows for a quantitative assessment of the thermodynamic efficiency limits of molecular D/A solar cells. Key parameters, apart from the optical gap of the absorber material, entering the model are the energy (ECT) and relative absorption strength (αCT) of the CT state. It is demonstrated how the open‐circuit voltage (VOC) and thus the power conversion efficiency are affected by different parameter values. Furthermore, it is shown that temperature dependent device characteristics can serve to determine the CT energy, and thus the upper limit of VOC for a given D/A combination, as well as to quantify non‐radiative recombination losses. The model is applied to diindenoperylene (DIP)‐based photovoltaic devices, with open‐circuit voltages between 0.9 and 1.4 V, depending on the partner, that have recently been reported.

Performance of Brick Aggregate Concrete at High Temperatures

This paper presents the results of an experimental investigation into the effects of high temperatures on the properties of concrete made with crushed clay bricks as the coarse aggregate. Two types of brick of different strength were crushed to coarse aggregate that was used to produce concretes of different strength. Natural granite aggregate was also used to produce concretes in order to compare results. The paper presents the results for brick unit uniaxial compressive strength, aggregate impact value, aggregate relative density, brick and aggregate water absorption, aggregate porosity, concrete density, and concrete strength before and after exposure to high temperatures. The results showed that concrete could be produced using crushed clay bricks as the coarse aggregate and at high temperatures clay brick concrete preformed similar or even better than granite concrete.

Hyperfine-structure splittings and absorption strengths of molecular-iodine transitions near the trapping frequencies of francium

Using saturated-absorption spectroscopy, we measured the hyperfine-structure splittings of four transitions in the B–X system of 127I2 near 718 nm, namely, of P(78)1–9, R(86)1–9, R(146)2–9, and R(113)3–10. The hyperfine constants ΔeQq and ΔC for these transitions were calculated from the measured splittings. Aided with Doppler line shapes calculated from the hyperfine splittings, and with knowledge of the relative absorption strengths of the nearby transitions from literature, we have measured the dipole moments of P(78)1–9, R(86)1–9, and R(113)3–10 from their integrated absorptions. These measurements, combined with Franck–Condon factors given in the literature, give an electronic transition dipole moment of 3.66(11)× 10−30 Cm [1.10(3) D] for the B–X system of iodine at an R-centroid internuclear distance of 0.293 nm.

High-velocity NaI and CaII absorption components observed towards the IC 443 SNR

We present high-resolution spectra ( km s-1) of the interstellar NaI and CaII interstellar absorption lines observed towards 4 early-type stars with distances of 900–1500 pc in the line-of-sight towards the IC 443 Supernova Remant (SNR). The spectra of two of these stars (HD 43582 and HD 254577) exhibit a very complex pattern of absorption with cloud components covering a total velocity range of -100 km s-1 to +50 km s-1. The relative absorption strength of many of the higher velocity components is highly variable between these two stars, suggesting that the disturbed interstellar gas in this region possesses significant density gradients and/or large differences in ionization and element depletion. In addition, we have detected three additional high-velocity components at , -84.0 and -67.6 km s-1 solely in their CaII lines, suggesting that the very highest velocity gas is more ionized and/or warmer than the lower velocity components or it has a highly variable level of gas phase element abundances. The column density ratios of NaI/CaII for the higher velocity cloud components are all <0.2, which is consistent with appreciable levels of dust grain destruction due to interstellar shocks caused by interaction of the expanding SNR blast-wave with the ambient interstellar medium. The distance to IC 443 is confirmed at ~1500 pc, which places the remnant at a similar distance to the Gem OB1 stellar association. Finally we note that the model of Chevalier (1999), in which the SNR is expanding into a clumpy interstellar medium, can best reproduce the observed patterns of both emission and absorption.

Blue and ultraviolet cathodoluminescence from Mn-doped epitaxial ZnO thin films

Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial Zn1−xMnxO thin films in a high throughput fashion. Local structures around Mn were investigated for these c-axis-oriented epitaxial films by fluorescence x-ray absorption fine structure measurements. It was shown that Mn substitutionally replaces Zn in Zn1−xMnxO (x&amp;lt;0.22) films. Well-structured blue and ultraviolet cathodoluminescence peaks corresponding to the intra-d-shell transitions of Mn2+ were observed, especially for smaller x. The luminescence is quenched rapidly as x is increased. By comparing the relative absorption strength per mole Mn2+ with the statistical probability of isolated Mn2+, it was concluded that the quick decrement of isolated Mn2+ with increasing x is responsible for the severe suppression of the blue and ultraviolet luminescence.

Effect of ablation parameters on infrared pulsed laser deposition of poly(ethylene glycol) films

Polymer thin films were deposited by laser ablation using infrared radiation both resonant (2.90, 3.40, 3.45, and 8.96 μm) and nonresonant (3.30, 3.92, and 4.17 μm) with vibrational modes in the starting material, polyethylene glycol. The chemical structure of the films was characterized by Fourier transform infrared spectroscopy, while the molecular weight distribution was investigated using gel permeation chromatography. The films deposited by resonant irradiation are superior to those deposited with nonresonant radiation with respect to both the chemical structure and the molecular weight distribution of the films. However, the molecular-weight distributions of films deposited at nonresonant infrared wavelengths show marked polymer fragmentation. Fluence and wavelength dependence studies show that the effects may be related to the degree of thermal confinement, and hence to the relative absorption strengths of the targeted vibrational modes.

Methyl iodide A-band decomposition study by photofragment velocity imaging

The methyl iodide A-band photodissociation process CH3I+hν→CH3(v,N,K)+I(2P3/2), I*(2P1/2) has been studied in a cold molecular beam. Full three-dimensional state-specific speed and angular distributions of the nascent fragments were recorded using (2+1) resonance-enhanced multi-photon ionization (REMPI) and velocity imaging, a new variant of ion imaging. By combining the I* quantum yield and anisotropy parameters for both I and I* channels, the relative absorption strength to the contributing electronic states (3Q0, Q13 and Q11) as well as the probability for curve crossing (3Q0→1Q1) are determined for excitation wavelengths across the full A band (240–334 nm). Parallel excitation to the Q03 state turns out to dominate the A band even more than previously thought.

Relative absorption strengths of neutral and negatively charged excitons in CdTe quantum wells

Excitonic absorption is studied in CdTe/Cd 1− x Zn x Te multiple quantum well samples that were double-doped in the barriers with indium donors and nitrogen acceptors. Under optical pumping, holes are trapped by acceptors and electrons form a 2D electron gas in the wells with power-dependent concentration n e. The absorption intensities of the neutral exciton X − and the charged exciton X − are measured in an 8 T field. As n e. varies from 0 upto about 10 11 cm −2, there is both a sharing of intensity between X and X − and an overall decrease of their summed absorption.

Relative absorption strengths of neutral and negatively charged excitons in CdTe quantum wells

Relative absorption strengths of neutral and negatively charged excitons in CdTe quantum wells

Spectroscopy of quasi-2D D − ions in the presence of excess electrons

Far infrared magneto-spectroscopic studies of quasi-2D D − ions have been carried out in several GaAs Al 0.3Ga 0.7As MQW samples with a wide range of controlled doping in the barrier with constant sheet doping in the well. Temperature, carrier density dependence, and polarization studies of a new confinement-related feature on the low frequency side of cyclotron resonance indicate that this feature is likely due to a D − triplet transition. The temperature dependence of the relative absorption strength of D −, D 0 and CR were also studied and found to be in qualitative agreement with a calculation that includes the probability of both single and double occupancy (the D − states) of a particular donor site in thermal equilibrium in high magnetic field.