Differential Absorption Cross Section Research Articles

Coherent multipolar amplification of chiroptical scattering and absorption from a magnetoelectric nanoparticle

Background-free detection of inherently weak chiroptical signals remains one of the great challenges in research communities and industries. We demonstrate coherent multipolar amplification of chiroptical responses via a magnetoelectric nanoparticle capped with an optically active monolayer encapsulated in a lossless background medium. Such an achiral nanoparticle can simultaneously support both electric and magnetic Mie-type resonances. We show how the combined excitation of orthogonal multipolar modes of the same order boosts the magnetoelectric coupling induced by the adsorbed chiral molecules, thus enabling coherently enhanced chiroptical responses from the ligand-capped magnetoelectric nanoparticle and allowing for absolute chirality measurements, in comparison with non-magnetoelectric nanoparticles. Furthermore, we develop rigorous expressions to separate relative contributions of chiral and nonchiral portions of circular differential absorption cross section, and analyzed the chirality-dependent far-field radiation patterns at different overlapped multipolar modes, providing a theoretical framework to understand the underlying enhancement mechanism of the magnetoelectric-assisted sensing of molecular chirality.

Collisions of low- to intermediate-energy electrons with acetonitrile

A systematic investigation was carried out on the elastic scattering of low- to intermediate-energy electrons ( = 0.1–1000 eV eV) by acetonitrile (CH3CN). We calculated differential (DCS), integral (ICS), momentum-transfer (MTCS), and total absorption cross sections from 0.1 to 1000 eV energy range using an absorption-effects-implemented ePolyScat-E3 suite of codes, which applies the Schwinger variational method combined with the Padé-approximants technique. Also, the screen-corrected independent atom model was used to compute DCSs, ICSs, and MTCSs from 10–1000 eV impact energies. Present results are compared to other theoretical and experimental data when available. In general, our DCS and MTCS results show a good agreement with available data, however, the ICSs and the resonance features exhibit fair accordance. Our results show two shape-resonance structures: one at about 3.4 eV and a second at about 7 eV. They are labeled as and , and comprise the and scattering channels, respectively.

Quantitative acquisition of differential absorption cross sections of chlorobenzenes at different temperatures

Chlorobenzene is considered an essential organic synthesis intermediate and a precursor for the generation of persistent organic compounds in the waste disposal process, for which accurate detection of gaseous chlorobenzene can further help understand and control various chemical processes and effectively reduce pollution. Differential optical absorption spectroscopy is a reliable online method for detecting gaseous chlorobenzenes. It is crucial to investigate the effect of temperature on the optical absorption of the chlorobenzenes to quantify chlorobenzenes more precisely at various temperatures. A method to fix the effect of temperature variation on absorption spectra of chlorobenzene is initially proposed in this study, and it gave accurate concentrations. The proposed method can effectively improve the accuracy of chlorobenzene concentration measurements with an inverse concentration deviation of 3.2 % or less. The differential absorption cross sections at various temperatures are studied to understand how chlorobenzene absorption cross sections vary with temperature. Such a study is also helpful in reducing the concentration inversion errors induced by the variation of absorption cross sections of chlorobenzene with temperature. A novel method of introducing the binary function of the differential absorption cross sections with respect to wavelength and temperature is also proposed. The fitting of the binary function is done by downscaling functions at fixed wavelength and fixed temperature,respectively. Both fitting approaches obtained continuous differential absorption cross sections in the 201–220 nm wavelength band and 288–473 K temperature range, along with less than 2.74 % deviation in the concentration inversion measurements. Finally,based on the temperature specificity of the shape of the differential absorption cross sections,we developed another method using differential absorption spectroscopy for the simultaneous measurement of temperature and concentration, with a temperature prediction error of less than 1.89 %. This method is favorable to the applications of differential absorption spectroscopy in simultaneous measurement of temperature and concentration.

Evaluation of systematic errors for the continuous-wave NO2 differential absorption lidar employing a multimode laser diode.

The NO2-differential absorption lidar (NO2-DIAL) technique has been of great interest for atmospheric NO2 profiling. Comprehensive studies on measurement errors in the NO2-DIAL technique are vital for the accurate retrieval of the NO2 concentration. This work investigates the systematic errors of the recently developed continuous-wave (CW) NO2-DIAL technique based on the Scheimpflug principle and a high-power CW multimode laser diode. Systematic errors introduced by various factors, e.g., uncertainty of the NO2 differential absorption cross-section, differential absorption due to other gases, spectral drifting of the λon and λoff wavelengths, wavelength-dependent extinction and backscattering effect, have been theoretically and experimentally studied for the CW-DIAL technique. By performing real-time spectral monitoring on the emission spectrum of the laser diode, the effect of spectral drifting on the NO2 differential absorption cross-section is negligible. The temperature-dependent NO2 absorption cross-section in the region of 220-294 K can be interpolated by employing a linear fitting method based on high-precision absorption spectra at 220, 240, and 294 K. The relative error for the retrieval of the NO2 concentration is estimated to be less than 0.34% when employing the interpolated spectrum. The primary interference molecule is found to be the glyoxal (CHOCHO), which should be carefully evaluated according to its relative concentration in respect to NO2. The systematic error introduced by the backscattering effect is subjected to the spatial variation of the aerosol load, while the extinction-induced systematic error is primarily determined by the difference between the aerosol extinction coefficients at λon and λoff wavelengths. A case study has been carried out to demonstrate the evaluation of systematic errors for practical NO2 monitoring. The comprehensive investigation on systematic errors in this work can be of great value for future NO2 monitoring using the DIAL technique.

Recent improvements of long-path DOAS measurements: impact on accuracy and stability of short-term and automated long-term observations

Abstract. Over the last few decades, differential optical absorption spectroscopy (DOAS) has been used as a common technique to simultaneously measure abundances of a variety of atmospheric trace gases. Exploiting the unique differential absorption cross section of trace-gas molecules, mixing ratios can be derived by measuring the optical density along a defined light path and by applying the Beer–Lambert law. Active long-path (LP-DOAS) instruments can detect trace gases along a light path of a few hundred metres up to 20 km, with sensitivities for mixing ratios down to ppbv and pptv levels, depending on the trace-gas species. To achieve high measurement accuracy and low detection limits, it is crucial to reduce instrumental artefacts that lead to systematic structures in the residual spectra of the analysis. Spectral residual structures can be introduced by most components of a LP-DOAS measurement system, namely by the light source, in the transmission of the measurement signal between the system components or at the level of spectrometer and detector. This article focuses on recent improvements by the first application of a new type of light source and consequent changes to the optical setup to improve measurement accuracy. Most state-of-the-art LP-DOAS instruments are based on fibre optics and use xenon arc lamps or light-emitting diodes (LEDs) as light sources. Here we present the application of a laser-driven light source (LDLS), which significantly improves the measurement quality compared to conventional light sources. In addition, the lifetime of LDLS is about an order of magnitude higher than of typical Xe arc lamps. The small and very stable plasma discharge spot of the LDLS allows the application of a modified fibre configuration. This enables a better light coupling with higher light throughput, higher transmission homogeneity, and a better suppression of light from disturbing wavelength regions. Furthermore, the mode-mixing properties of the optical fibre are enhanced by an improved mechanical treatment. The combined effects lead to spectral residual structures in the range of 5-10×10-5 root mean square (rms; in units of optical density). This represents a reduction of detection limits of typical trace-gas species by a factor of 3–4 compared to previous setups. High temporal stability and reduced operational complexity of this new setup allow the operation of low-maintenance, automated LP-DOAS systems, as demonstrated here by more than 2 years of continuous observations in Antarctica.

Waveguide-based electro-absorption modulator performance: comparative analysis.

Electro-optic modulators perform a key function for data processing and communication. Rapid growth in data volume and increasing bits per second rates demand increased transmitter and thus modulator performance. Recent years have seen the introduction of new materials and modulator designs to include polaritonic optical modes aimed at achieving advanced performance in terms of speed, energy efficiency, and footprint. Such ad hoc modulator designs, however, leave a universal design for these novel material classes of devices missing. Here we execute a holistic performance analysis for waveguide-based electro-absorption modulators and use the performance metric switching energy per unit bandwidth (speed). We show that the performance is fundamentally determined by the ratio of the differential absorption cross-section of the switching material's broadening and the waveguide effective mode area. We find that the former shows highest performance for a broad class of materials relying on Pauli-blocking (absorption saturation), such as semiconductor quantum wells, quantum dots, graphene, and other 2D materials, but is quite similar amongst these classes. In this respect these materials are clearly superior to those relying on free carrier absorption, such as Si and ITO. The performance improvement on the material side is fundamentally limited by the oscillator sum rule and thermal broadening of the Fermi-Dirac distribution. We also find that performance scales with modal waveguide confinement. Thus, we find highest energy-bandwidth-ratio modulator designs to be graphene, QD, QW, or 2D material-based plasmonic slot waveguides where the electric field is in-plane with the switching material dimension. We show that this improvement always comes at the expense of increased insertion loss. Incorporating fundamental device physics, design trade-offs, and resulting performance, this analysis aims to guide future experimental modulator explorations.

Ultraviolet differential spectroscopy quantitative analysis of SF 6 decomposition component SO 2

SO2 is a symbolic gas that can indicate the insulation status of SF6 insulation electrical equipment. Its accurate quantitative measurement is of the great significance for the judgement of the type and severity of faults inside the insulation equipment. For this reason, a detection system of trace SO2 based on ultraviolet (UV) spectrometry was presented. The measured UV absorption spectra of SO2 were processed using the wavelet analysis to remove useless spectra information and get the UV differential absorption spectra of SO2. The fast Fourier transform (FFT) was used to analyse UV differential spectra in the band of 190–230 and 290–310 nm and extract the feature information. The results show that there is a good linear relationship between the FFT characteristic peak value and the concentration of trace SO2 in the two wave bands. The detection limit in the band of 190–230 nm was even lower than that in the band of 290–310 nm. Besides, the differential absorption cross section of SO2 decreases with the increase of temperature. The study has laid a foundation for the application of the UV differential absorption spectroscopy in the online monitoring and fault diagnosis of SF6 insulation electrical equipment.

Greybody factor of a scalar field from Reissner\u2013Nordstr\xf6m\u2013de Sitter black hole

In this work we derive a general expression for the greybody factor of non-minimally coupled scalar fields in Reissner–Nordström–de Sitter spacetime in low frequency approximation. Greybody factor as a characteristic of effective potential barrier, will be presented. We discuss the role of cosmological constant both, in the absence as well as in the presence of non-minimal coupling. Considering non-minimal coupling as a mass term, its effect on the greybody factor will be discussed. We also elaborate the significance of the results by giving formulae of differential energy rate and general absorption cross section. The greybody factor gives insight into the spectrum of Hawking radiations.

A miniDOAS instrument optimised for ammonia field measurements

Abstract. We present a differential optical absorption spectroscopy (DOAS) instrument, called "miniDOAS", optimised for optical open-path field-measurements of ambient ammonia (NH3) alongside nitrogen oxide (NO) and sulfur dioxide (SO2). The instrument is a further development of the miniDOAS presented by Volten et al. (2012). We use a temperature-controlled spectrometer, a deuterium light source and a modified optical arrangement. The system was set up in a robust, field-deployable, temperature-regulated housing. For the evaluation of light spectra we use a new high-pass filter routine based upon robust baseline extraction with local regression. Multiple linear regression including terms of an autoregressive–moving-average model is used to determine concentrations. For NH3 the random uncertainty is about 1.4 % of the concentration, and not better than 0.2 µg m−3. Potential biases for the slope of the calibration are given by the precision of the differential absorption cross sections (±3 %) and for the offset by the precision of the estimation of concentration offsets (cref) introduced by the reference spectrum Iref. Comparisons of miniDOAS measurements to those by NH3 acid trap devices showed good agreement. The miniDOAS can be flexibly used for a wide range of field trials, such as micrometeorological NH3 flux measurements with approaches based upon horizontal or vertical concentration differences. Results from such applications covering concentration dynamics of less than one up to several hundreds of µg m−3 are presented.

Sensitivity of on-line wavelength during retrieval of atmospheric CO_2 vertical profile

Accurately measuring the differential molecular absorption cross section is the key to obtaining a high-precision concentration of atmospheric trace gases in a differential absorption lidar (DIAL) system. However, the CO2 absorption line is meticulous at 1.6 μm, easily translating and broadening because of the change of temperature and pressure. Hence, measuring the vertical profile of atmospheric temperature and pressure to calculate the vertical profile of the CO2 weight parameter is necessary. In general, measuring atmospheric temperature and pressure has a certain amount of uncertainty. Therefore, this study proposes the concept of a balanced on-line wavelength, where the differential molecular absorption cross section is larger and the CO2 weight parameter is insensitive to the uncertainty of atmospheric temperature and pressure. In this study, we analyzed the influence of uncertainty on the CO2 weight parameter at every preselected wavelength, as well as determined an appropriate wavelength near one of the absorption peaks. Our result shows that 1572.023 nm should be one of the appropriate balanced on-line wavelengths. The measurement errors of the mixing ratio of CO2 molecule in this wavelength are only 0.23% and 0.25% and are caused by 1 K temperature error and 1 hPa pressure error, respectively. This achievement of a balanced on-line wavelength will not only depress the requirement of the laser’s frequency stabilization but also the demand for measurement precision of the atmospheric temperature and pressure profile. Furthermore, this study can achieve the exact measurement of the vertical profile of atmospheric CO2 based on an independent differential absorption laser.

System design and performance simulation of ground-based differential absorption lidar for water-vapor measurements

In order to obtain water-vapor profiles in the lower troposphere with a high accuracy and a temporal-spatial resolution, an improved ground-based differential absorption lidar system for water-vapor measurements is demonstrated. The key components of the system and the errors possibly existing in the system are described in detail. A real-time differential absorption cross-section measurement device that can compensate for measuring error caused by laser transmitter is presented. Combined with the water-vapor concentrations of different seasons in Shanghai, the differential optical thickness, the relationship between the gain of avalanche photo-diodes and the signal to noise ratio of received signal, and the statistical error in detection of four absorption lines in the 935 nm H2O absorption band are simulated in detail. The result shows that a particular absorption line can be selected, which depends on season and meteorological condition, to achieve the best outcome. With a time resolution of 5 min and a vertical resolution of 300 m, the statistical error of water vapor concentration is no more than 18% in a range of 300-5000 m.

Study on Detection of Environmental Air Pollution by Differential Optical Absorption Spectrometry

High quality air environment is needed for human health. Indoor air pollution comes from surface decoration materials and outdoor smoke pollution. In this paper, based on Differential Optical Absorption Spectrometry (DOAS), absorption spectra of main pollution gases HCHO, SO2, NO, NO2 are measured and their differential absorption cross sections are calculated. For ppm range of pollutant concentration, minimum measurement error of 9% is achieved by our experiments. It is sensitive for air pollution detection.

Optical Transition, Excitation State Absorption, and Energy Transfer Study of Er3+, Nd3+ Single-Doped, and Er3+/Nd3+ Codoped Tellurite Glasses for Mid-Infrared Laser Applications

Nd 3+ , Er 3+ single-doped and Nd 3+ /Er 3+ codoped tellurite glasses were prepared via a melt-quenching technique, and their optical transition properties were studied in the framework of Judd-Ofelt theory. The differential excited state absorption cross section from 4 I 13/2 to 4 I 11/2 was obtained based on the McCumber theory; furthermore, the optical gain coefficient spectrum for 4 I 11/2 → 4 I 13/2 transition was calculated. The energy transfers 4 F 3/2 (Nd 3+ )+ 4I 15/2 (Er 3+ )→ 4 I 9/2 (Nd 3+ )+ 4 I 9/2 (Er 3+ ) and 4 I 13/2 (Er 3+ )+ 4 I 9/2 (Nd 3+ )→ 4 I 15/2 (Er 3+ )+ 4 I 15/2 (Nd 3+ ) in the codoped sample were analyzed by using Foster-Dexter theory and Inokuti-Hirayama's model, respectively ; meanwhile, the energy transfer rates for both the energy transfer processes were confirmed. The results indicated that Nd 3+ may be a good sensitizer for Er 3+ to obtain intense mid-infrared emission, and that Nd 3+ /Er 3+ codoped tellurite glass may be a good candidate media for mid-infrared lasers.

ChemInform Abstract: Near-UV Absorption Cross Sections and Trans/Cis Equilibrium of Nitrous Acid.

The A {sup 1}A{double prime} {l arrow} X {sup 1}A{prime} absorption spectrum of gaseous nitrous acid has been measured in the 300-400-nm range. Absolute cross sections were determined by a combination of gas-phase and wet chemical analysis. The cross sections of prominent bands are 25% larger than the recommended values of Stockwell and Calvert. The influence of spectral resolution on absolute and differential absorption cross sections was also investigated. The integrated band area of the n{pi}* transition yields an oscillator strength f = (8.90 {plus minus} 0.36) {times} 10{sup {minus}4}, less than the reported liquid phase value of 2 {times} 10{sup {minus}3}. The equilibrium constant K = p{sub trans}/p{sub cis}, based on the assumption that the oscillator strength of the n{pi}* transition is the same for both rotamers, was found to be 3.25 {plus minus} 0.30 at 277 K. This yields an energy difference {Delta}E between trans- and cis-HONO of -2,700 J mol{sup {minus}1} in the electronic ground state, and -6,000 J mol{sup {minus}1} in the excited state.

Low concentration iodine molecules lidar sensing

Lidar monitoring of the gaseous molecules in atmosphere can be used for concentration measurements of the toxic pollutants in the air of the urban and industrial regions. Such a concentration studies in the multi-components gaseous mixture essentially by lidar technique is a complex problem in atmospheric pollution monitoring. There are the fluorescence lidar and differential absorption lidar the most preferable for the detection of iodine molecules at very low concentration levels. Laboratory lidar studies and lidar equation simulation in these lidar variants gave the iodine molecules fluorescence differential cross section and iodine molecules absorption cross section in good agreement with earlier data. The experimental results confirm the possibility of the molecular iodine lidar sensing at low pressure and the measuring results treatment allows to get iodine molecules parameters.

Anharmonic bend–stretch coupling in neat liquid water

Femtosecond mid-IR spectroscopy is used to study the vibrational relaxation dynamics in neat liquid water. By exciting the bending vibration and probing the stretching mode, it is possible to reliably determine the bending and librational lifetimes of water. The anharmonic coupling between the bending and the stretching degrees of freedom is quantified in terms of a differential absorption cross-section for the fundamental stretching transition carrying one spectating bending quantum. A positive off-diagonal anharmonicity may be caused by the initial excitation of the anharmonic bending mode and is mediated by the hydrogen bonded network.

Investigation of the formaldehyde differential absorption cross section at high and low spectral resolution in the simulation chamber SAPHIR

Abstract. The results from a simulation chamber study on the formaldehyde (HCHO) absorption cross section in the UV spectral region are presented. We performed 4 experiments at ambient HCHO concentrations with simultaneous measurements of two DOAS instruments in the atmosphere simulation chamber SAPHIR in Jülich. The two instruments differ in their spectral resolution, one working at 0.2 nm (broad-band, BB-DOAS), the other at 2.7 pm (high-resolution, HR-DOAS). Both instruments use dedicated multi reflection cells to achieve long light path lengths of 960 m and 2240 m, respectively, inside the chamber. During two experiments HCHO was injected into the clean chamber by thermolysis of well defined amounts of para-formaldehyde reaching mixing rations of 30 ppbV at maximum. The HCHO concentration calculated from the injection and the chamber volume agrees with the BB-DOAS measured value when the absorption cross section of Meller and Moortgat (2000) and the temperature coefficient of Cantrell (1990) were used for data evaluation. In two further experiments we produced HCHO in-situ from the ozone + ethene reaction which was intended to provide an independent way of HCHO calibration through the measurements of ozone and ethene. However, we found an unexpected deviation from the current understanding of the ozone + ethene reaction when CO was added to suppress possible oxidation of ethene by OH radicals. The reaction of the Criegee intermediate with CO could be 240 times slower than currently assumed. Based on the BB-DOAS measurements we could deduce a high-resolution cross section for HCHO which was not measured directly so far.

One- and two-photon picosecond excitation dynamics of the singlet states of a tetraphenyl-diamine derivative in solution

We report on nonlinear absorption measurements of a tetraphenyl-diamine dye which was developed to be used as a transparent two-photon-type molecular material for optical limiting applications in the visible range. The excited state properties which are relevant to the process are investigated experimentally using picosecond nonlinear optical Kerr ellipsometry for differential absorption cross section monitoring. Results of the picosecond one- and two-photon absorption dynamics are presented. Time-resolved excited state absorption properties are discussed in terms of the optical limiting application.

Alternative method for concentration retrieval in differential optical absorption spectroscopy atmospheric-gas pollutant measurements.

Differential optical absorption spectroscopy is a widely used technique for open-column atmospheric-gas pollution monitoring. The concentration retrieval is based on the fitting of the measured differential absorbance through the Lambert-Beer law. We present an alternative method for calculating the gas concentration on the basis of the proportionality between differential absorbance and differential absorption cross section of the gas under study. The method can be used on its own for single-component analysis or as a complement to the standard technique in multicomponent cases. The performance of the method for the case of cross interference between two gases is analyzed. The procedure can be used with differential absorption cross sections measured in the laboratory or taken from the literature. In addition, the method provides a criterion to discriminate against different species having absorption features in the same wavelength range.

Kinetics of the ClO Self-Reaction and 210 nm Absorption Cross Section of the ClO Dimer

The kinetics of the dimerization of ClO radicals, ClO + ClO + M → Cl2O2 + M (1a), and the 210 nm absorption cross sections of the ClO dimer have been studied using the technique of flash photolysis with UV absorption spectroscopy, over the temperature range 183−245 K and pressure range 25−700 Torr. ClO radicals were generated following the photolysis of Cl2/Cl2O/N2 mixtures and were quantified via their differential absorption between the peak of the (12,0) band of the (Ã ← X̃) transition at 275.2 nm and the adjacent minimum to higher wavelengths, while Cl2O2 formation was simultaneously monitored at 210 nm. ClO differential absorption cross sections were measured under identical conditions to the kinetic experiments by four separate calibration schemes. The rate coefficient measured at the lower temperatures studied (T < 200 K) was found to be up to 40% faster than extrapolation of previous results would suggest, with the limiting low- and high-pressure rate coefficients for reaction 1 in nitrogen determined to be k0 = (1.59 ± 0.60) × 10-32 × (T/300)-4.50±0.98 molecules-2 cm6 s-1 and k∞ = (1.36 ± 0.22) × 10-12 × (T/300)-3.09±0.40 molecules-1 cm3 s-1 respectively, obtained with Fc = 0.6. The corresponding value for k0 in air is k0(atm) = (1.49 ± 0.56) × 10-32 × (T/300)-4.50±0.98 molecules-2 cm6 s-1. The 210 nm absorption cross section of Cl2O2 was measured following time-resolved monitoring of its formation via ClO radical association, and a mean value of (2.94 ± 0.86) × 10-18 molecule-1 cm2 obtained, temperature independent (to within ± 15%) between 183 and 245 K. Errors are combined systematic uncertainties and 2 standard deviations statistical variation.