Spectral Line Position Research Articles

Thermal dissociation of free and acceptor-bound positive trions from magnetophotoluminescence studies of high qualityGaAs/AlxGa1−xAsquantum wells

Thermal dissociation of free and acceptor-bound quasi-two-dimensional positive trions is investigated by measuring the temperature dependence of the integrated emission intensity in magnetic fields up to 17 T in high quality GaAs/AlxGa1-xAs quantum wells. Three distinct dissociation processes are observed for the well-resolved hole cyclotron replicas (shake-up) of positive trions bound to neutral acceptors in the spin-doublet state (SU-A0Xd+). To demonstrate that the hole involved in the shake-up process is not bound by the Coulomb interaction to the charged A0X+ complex, we calculate the valence Landau levels using the Luttinger model beyond the axial approximation. The calculated value of the hole cyclotron energy agrees well with the experimental data for the energy separation of the A0X+ and SU-A0X+ lines, determined from the emission spectra. At low temperatures, below 6 K, the dominant dissociation results in a free hole and an exciton bound to the neutral acceptor in the spin-singlet or -triplet state, (A0Xd+→A0Xs+h or A0Xt+h). At higher temperatures, above 9 K, the dissociation into the free positive trion and the neutral acceptor (A0Xd+→A0+X+) predominates. From the temperature evolution of the integrated emission of the free trion lines (X+) we evaluate the transition energy between the two triplet trion states, the dark one (Xtd+) and the bright one (Xtb+). The ionization energies of all detected dissociation processes are compared with the spectral positions of the relevant radiative recombination lines from which excellent quantitative agreement is achieved.

Study on the methods of calibrating spectral line position of interference imaging spectrometer

The principle of interference imaging spectrometer is presented. According to the drift of recovery spectral line position, two representative methods of calibrating the laboratory spectral line position are proposed, and the calibration results and their comparative analyses are given. One method of calibration is to correct the principle, which embarks from parameter selection of interference imaging spectrometer and the analysis of the reason why the spectral line position is drifted. Aiming at the problem that the position of spectral line changes with row, the correction scheme is given to improve the accuracy of spectral line position. For four given laser wavelengths, which are 543.5 nm, 594.1 nm, 612 nm, and 632.8 nm, the root-mean-square (RMS) error of spectral line position is reduced from 28.3914 to 5.5371 after calibration. For the interferometer system which has no dispersion, the accuracy of calibration is better than the dispersion system, and can be the same at all detected wavelengths. In this article, the calibration accuracy of long wave is better than that of short wave, which is dependent on the selection of the initial correction wavelength. This method achieves a kind of universality for interference imaging spectrometer and its calibration parameters provide a convenient way to analyze the instrument indexes. Another calibration method is data processing. It makes up the deficiencies of the method mentioned above: a large number of data are needed and the effect of calibration at short wave is not good enough. The RMS error of spectral line position is reduced to 0.9178, which proves that the calibration has a really high precision. This method is simple and can correct all the detected wavelengths and spectral lines by using two united formula. Though this method is not applicable for all the interference imaging spectrometers, the idea that makes hard things simple is deserving of our attention. We can use it in many other fields. The essence of the method is to change a variable quantity into a slowly varying quantity by algorithms, and then establish the relationship between the slowly varying quantity and the standard value. This idea can always make a substantial increase in efficiency of calibration and has a satisfied accuracy. Each of the two methods has advantages and disadvantages: which method we choose to use is dependent on the effect we want to achieve, and it is better to make their combination. This study provides a theoretical and practical guidance for study, design, modulation, experiment and engineering of interference imaging spectrometers.

Reconstruction of polarization parameters in channel modulated polarization imaging system

Based on the reconstruction of the polarization parameters in a channel modulating polarization imaging system, the polarization features of the target could be extracted effectively. Considering that the reconstruction of polarization parameters can provide important reference for target recognition, material analysis, remote sensing and bio-medical treatment, the research on accurate reconstruction of polarization parameters is now urgently required. In order to improve the accuracy of polarization parameter reconstruction, we first study the influence of sample frequency of interference fringes on the imaging process. For the same carrier frequency, conjugate spectra are separated and also the spectra are not aliasing for two adjacent spectral lines. It is concluded that to prevent the image spectrum from aliasing, the sample frequency should be at least 4 times the maximum fringe frequency of the polarization interference image. Then we study Stokes parameter reconstruction method when the spectral line positions of interference image are changed by assembling error. Since different Stokes parameters are amplitude modulated at different frequencies, we apply segment filters to split the frequency domain into different regions, and seek for the largest spectrum in corresponding regions. The largest spectrum in different regions can be used to determine the spectral line position of polarization carrier frequency, and the two-dimensional images of the target are rebuilt in sequence by the frequency shifting, spectral filtering, and Fourier inversion transforming. According to the above method, we could obtain an exact polarization rebuilding image when the line position of polarization carrier frequency is modified. Finally, we use the computer simulation and experiment to verify the feasibility and effectiveness of such a rebuilding method. The results demonstrate that the reconstruction of polarization parameters in channel modulating polarization imaging by this rebuilding method is better than by the traditional theoretical rebuilding method. In detail, the mean square error between the reconstruction and original input image could be suppressed to 0.001 while the peak-signal-to-noise ratio is improved and the structural similarity index measurement could be more than 0.9 by utilizing the new rebuilding method. It turns out that the reconstruction method with great superiority can provide a promising reference for further research of channel modulating polarization imaging system.

Doppler methods of search and monitoring of exoplanets

The main stages of the development of Doppler methods of search and study of extrasolar planetary systems (exoplanets) are described. The main instrumental and methodological effects that influence the measurement accuracy of spectral line positions in the study of exoplanets are considered. The development of the domestic spectrograph for spectroscopic monitoring with high-precision determination of radial velocities is reported. Directions for further development of high-resolution spectroscopy are discussed.

Laser spectroscopy of jet-cooled NiF: Application of Hougen’s approximate model for the low-lying electronic states

We have taken laser-induced fluorescence spectra of jet-cooled nickel monofluoride formed in a laser-ablation molecular beam source. Dispersed-fluorescence spectroscopy confirms predictions by Hougen (2011) that the parity assignments of levels in the Ω=1/2 state 1570cm−1 above the ground state should be reversed from those given in Krouti et al. (2002). The quality of the high-resolution spectra was sufficient to measure the [22.9]1.5–X1.5 band for five isotopologues of nickel and the [22.9]1.5–[0.25]0.5 band for molecules containing 58Ni and 60Ni. The spectral line positions for each isotopologue were fit to the Hamiltonian model given by Hougen, which was extended to allow for calculation of the parity-splitting parameter in the ground state.

Laser ablation molecular isotopic spectrometry of carbon isotopes

Quantitative determination of carbon isotopes using Laser Ablation Molecular Isotopic Spectrometry (LAMIS) is described. Optical emission of diatomic molecules CN and C2 is used in these measurements. Two quantification approaches are presented: empirical calibration of spectra using a set of reference standards and numerical fitting of a simulated spectrum to the experimental one. Formation mechanisms of C2 and CN in laser ablation plasma are briefly reviewed to provide insights for implementation of LAMIS measurements. A simulated spectrum of the 12C2 Swan system was synthesized using four constituents within 473.5–476.5nm. Simulation included three branches of 12C2 (1-0), branches R(0-0) and R(1-1), and branch P(9-8) of 12C2. Spectral positions of the tail lines in R(0-0) and R(1-1) were experimentally measured, since they were not accurately known before. The Swan band (1-0) of the isotopologue 13C12C was also simulated. Fitting to the experimental spectrum yielded the ratio 13C/12C=1.08% in a good agreement with measurements by isotope ratio mass spectrometry. LAMIS promises to be useful in coal, oil and shale exploration, carbon sequestration monitoring, and agronomy studies.

Line shape of amplitude or frequency-modulated spectral profiles including resonator distortions.

We report experiments and an improved method of analysis for any harmonics of frequency-modulated spectral line shapes allowing for very precise determinations of the resonance frequency of single absorption lines for gigahertz spectroscopy in the gas phase. Resonator perturbations are implemented into the formalism of modulation spectroscopy by means of a full complex transmission function being able to model the asymmetrically distorted absorption line shapes for arbitrary modulation depths, modulation frequencies, and resonator reflectivities. Exact equations of the in-phase and the quadrature modulation signal, taking into account a full resonator transmission function, are simultaneously adjusted to two-channel lock-in measurements performed in the gigahertz regime to obtain the spectral line position. The determination of the absorption line position of the rotational transition J' = 7 ← J" = 6 of (16)O(12)C(32)S in the vibrational ground state is investigated while changing the resonator distortions. The results are subjected to the approach proposed here and compared to standard methods known from the literature.

Bichromatic laser-induced quadrupole-dipole collisional energy transfer in Ca-Sr.

We consider the response of a laser-induced quadrupole-dipole collisional system driven by a strong dressing laser field with the aim of calculating the collisional cross section of a weak inducing laser probe. The addition of a second driving field to the traditional arrangement will cause magnitude changes of the spectra and modify the profile. The calculation results show that the bichromatic laser-induced collisional energy-transfer process can be an efficient way to probe Stark splitting of both the final state and intermediate state. The magnitude and position of the splitting spectral lines are strongly dependent on the intensity of the dressing laser field. The peak cross section almost reduces by a factor of 2 with the presence of the dressing laser. Also, in the antistatic wing, bright and dark lines are periodic, appearing with the increasing of the dressing laser intensity.

Dynamics of telescopic cranes with flexible structural components

Today׳s crane numerical models are devoid of some of the simplifications that were used in the past. These changes primarily take into account flexibilities of those structural components that used to be treated as non-deformable. Consequently, various studies analyse the same working movements based on different models.The paper presents ten variants of a computational model for a telescopic boom crane that differs in number and selection of flexible components. It has been analysed how the above-mentioned differences affect the correctness of mapping the dynamic properties of real structures via their computational models. Modelling and numerical simulations were conducted using the finite element method. The compatibility of the numerical simulation results and test results of a real structure was qualitatively and quantitatively assessed. Time characteristics and frequency characteristics after application of the discrete Fourier transformation were analysed. The analyses showed that the parameters of the modified components should be determined by taking into account their interactions with their surroundings in order to ensure correctness of the solutions. A comparison of the shape and position of spectral lines with respect to changes in the overall flexibility of the models facilitates in deciding which components should be modified and which should be omitted in order to correctly imitate the dynamic properties of a real structure.

Tuning Characteristics of DFB Diode Laser and its Application to TDLAS Gas Sensor Design

Static and dynamic tuning characteristics of Distribute Feedback (DFB) diode lasers are investigated with practical laser devices. These characteristics are the basic guidelines for practical TDLAS sensors design. Static tuning characteristics help to select suitable diode lasers from limited available laser devices with specific wavelength and to set an appropriate working current and temperature. Dynamic tuning characteristics decide the sweep speed of current slope in both direct absorb Spectroscopy (DAS) and wavelength modulation Spectroscopy (WMS). Because of nonlinearity in the relation between wavelength and tuning current, the measured spectral line position should be corrected by the dynamic characteristics. For WMS, current tuning efficient and IM/AM (Intense modulation/Amplitude modulation) differential phase could be utilized to optimize laser modulation and harmonic components demodulation.

Atomic data and theoretical X-ray spectra of Ge-like through V-like W ions

The atomic structure and spectra of ten tungsten ions have been calculated using the Flexible Atomic Code. The calculations yield energy levels, radiative lifetimes, spectral line positions, transition probability rates, and oscillator strengths for the tungsten ions isoelectronic to germanium, W42+, through vanadium, W51+. Collisional–radiative models for high-temperature, low-density plasmas have been implemented to produce line emissivities for X-ray transitions in the 1–4 keV (3–12 Å) spectral interval. The Ge-like through V-like W ions are important in nuclear fusion research where their spectra may provide diagnostic information on magnetically confined plasmas.

Effect of temperature on optical spectra and relaxation dynamics of Sm3+ in Gd3Ga5O12 single crystals

Single crystals of Gd3Ga5O12 (GGG) doped with 2 at.% and 10 at.% of Sm3+ were fabricated by the Czochralski method. Optical absorption and emission spectra as well as luminescence decay curves for these crystals were recorded at different temperatures ranging from 5 K to 300 K. The energies of the crystal field sublevels of selected multiplets were determined based on optical spectra recorded at T = 5 K. It has been found that widths of spectral lines related to transitions between individual crystal field levels of multiplets involved increase by factors of 5–7 when the sample temperature grows from 5 K to 300 K. In contrast to this the positions of spectral lines appear to be independent of temperature. Temperature dependence of the 4G5/2 luminescence lifetime was determined for both concentrations of samarium. Luminescence decay curves follow a single-exponential time dependence when Sm3+ concentration amounts to 2 at.% but a non-exponential decay kinetic and efficient quenching process were observed in highly-doped sample. The Inokuti–Hirayama classical energy transfer model was utilized successfully to account for time dependence of an experimental decay curves recorded for GGG:10 at.% Sm crystal.

Laser frequency scale system in carbon isotopic abundance measurement

The real-time laser frequency scale system is developed for measuring the carbon isotopic abundance. By using confocal Fabry-Perot interferometer with different free spectral ranges, the diode laser frequency tuning characteristic is acquired in each laser frequency scanning period. During the course of measurements, two nonlinear analysis techniques are tested, i.e., linear interpolation and polynomial fitting. The absorption line center position for CO2 between 4976 and 4980 cm-1 is obtained by 100 average measurements from our experiments. A comparison between the measured absorption spectra and the spectral line positions from the HITRAN-2008 database, shows that the two method can both reach an accuracy of 10-4 cm-1 for the laser frequency scale. The best results are obtained with a linear interpolation method. The result shows that the laser frequency real-time scale system is applicable in carbon isotopic abundances measurement.

Decoding Pure Rotational Molecular Spectra for Asymmetric Molecules

Rotational spectroscopy can provide insights of unparalleled precision with respect to the wavefunctions of molecular systems that have relevance in fields as diverse as astronomy and biology. In this paper, we demonstrate how asymmetric molecular pure rotational spectra may be analyzed “pictorially” and with simple formulae. It is shown that the interpretation of such spectra relies heavily upon pattern recognition. The presentation of some common spectral line positions in near-prolate asymmetric rotational spectra provides a means by which spectral assignment, and approximate rotational constant determination, may be usefully explored. To aid in this endeavor we have created a supporting, free, web page and mobile web page.

Phase-difference and spectroscopic imaging for monitoring of human brain temperature during cooling

Decrease of the human brain temperature was induced by intranasal cooling. The main purpose of this study was to compare the two magnetic resonance methods for monitoring brain temperature changes during cooling: phase-difference and magnetic resonance spectroscopic imaging (MRSI) with high spatial resolution. Ten healthy volunteers were measured. Selective brain cooling was performed through nasal cavities using saline-cooled balloon catheters. MRSI was based on a radiofrequency spoiled gradient echo sequence. The spectral information was encoded by incrementing the echo time of the subsequent eight image records. Reconstructed voxel size was 1×1×5 mm3. Relative brain temperature was computed from the positions of water spectral lines. Phase maps were obtained from the first image record of the MRSI sequence. Mild hypothermia was achieved in 15–20 min. Mean brain temperature reduction varied in the interval <−3.0; −0.6>°C and <−2.7; −0.7>°C as measured by the MRSI and phase-difference methods, respectively. Very good correlation was found in all locations between the temperatures measured by both techniques except in the frontal lobe. Measurements in the transversal slices were more robust to the movement artifacts than those in the sagittal planes. Good agreement was found between the MRSI and phase-difference techniques.

A consistent approach for mixed detailed and statistical calculation of opacities in hot plasmas

Absorption and emission spectra of plasmas with multicharged-ions contain transition arrays with a huge number of coalescent electric-dipole (E1) lines, which are well suited for treatment by the unresolved transition array and derivative methods. But, some transition arrays show detailed features whose description requires diagonalization of the Hamiltonian matrix. We developed a hybrid opacity code, called SCORCG, which combines statistical approaches with fine-structure calculations consistently. Data required for the computation of detailed transition arrays (atomic configurations and atomic radial integrals) are calculated by the superconfiguration code SCO ( Super-Configuration Opacity), which provides an accurate description of the plasma screening effects on the wave-functions. Level energies as well as position and strength of spectral lines are computed by an adapted RCG routine of R. D. Cowan. The resulting code provides opacities for hot plasmas and can handle mid- Z elements. The code is also a powerful tool for the interpretation of recent laser and Z-pinch experimental spectra, as well as for validation of statistical methods.

Elemental misinterpretation in automated analysis of LIBS spectra

In this work, the Stark effect is shown to be mainly responsible for wrong elemental allocation by automated laser-induced breakdown spectroscopy (LIBS) software solutions. Due to broadening and shift of an elemental emission line affected by the Stark effect, its measured spectral position might interfere with the line position of several other elements. The micro-plasma is generated by focusing a frequency-doubled 200 mJ pulsed Nd/YAG laser on an aluminum target and furthermore on a brass sample in air at atmospheric pressure. After laser pulse excitation, we have measured the temporal evolution of the Al(II) ion line at 281.6 nm (4s(1)S-3p(1)P) during the decay of the laser-induced plasma. Depending on laser pulse power, the center of the measured line is red-shifted by 130 pm (490 GHz) with respect to the exact line position. In this case, the well-known spectral line positions of two moderate and strong lines of other elements coincide with the actual shifted position of the Al(II) line. Consequently, a time-resolving software analysis can lead to an elemental misinterpretation. To avoid a wrong interpretation of LIBS spectra in automated analysis software for a given LIBS system, we recommend using larger gate delays incorporating Stark broadening parameters and using a range of tolerance, which is non-symmetric around the measured line center. These suggestions may help to improve time-resolving LIBS software promising a smaller probability of wrong elemental identification and making LIBS more attractive for industrial applications.

Crystal Structure, Spectroscopy and Crystal Field Analysis of Substituted 1,10‐Phenanthroline–Europium Complexes

AbstractCrystal structures and vibrational and electronic spectroscopic data are reported for europium(III) complexes with 5(or 4)‐R‐1,10‐phenanthroline (phen) ligands (R = chloro, methyl, nitro, amino). All complexes comprise a 10‐coordinate Eu3+ ion with three chelating nitrato anions and two bidentate phen ligands. The crystal structures are of three distinct types with space groups C2/c, P21/n and P. The room‐temperature emission spectra are dominated by the forced electric dipole 5D0 → 7F2 emission of Eu3+. The excitation spectra show that the triplet donor state of the nitro‐substituted complex has a lower energy than the other complexes and the lower luminescence quantum efficiency of this complex is rationalized. The emission spectra recorded at 10 K have been compared with those of the corresponding Eu3+‐doped yttrium complexes using different excitation lines as a criterion of sample purity. The spectrum of the unsubstituted phen complex is more clearly resolved than those of the other complexes and this has been attributed to disorder resulting in inhomogeneous broadening. A detailed crystal field analysis is given for the phen complex from the fitting of 24 crystal field energy levels. A comparison with other complexes has been made through derived second‐rank crystal field strengths. No simple relationships have been derived from comparisons of energy levels, spectral line positions, or second‐rank crystal field strengths with crystallographic data or Taft constants.

High-resolution synchrotron-based Fourier transform spectroscopy of in the 120–350 cm−1 far-infrared region

The Fourier transform spectrum of the isotopologue of methanol has been recorded in the 120–350 cm−1 far-infrared region at a resolution of 0.00096 cm−1 using synchrotron source radiation at the Canadian Light Source. The study, motivated by astrophysical applications, is aimed at generating a sufficiently accurate set of energy level term values for the ground vibrational state to allow prediction of the centres of the quadrupole hyperfine multiplets for astronomically observable sub-millimetre transitions to within an uncertainty of a few MHz. To expedite transition identification, a new function was added to the Ritz program in which predicted spectral line positions were generated by an adjustable interpolation between the known assignments for the and isotopologues. By displaying the predictions along with the experimental spectrum on the computer monitor and adjusting the predictions to match observed features, rapid assignment of numerous sub-bands was possible. The least squares function of the Ritz program was then used to generate term values for the identified levels. For each torsion-K-rotation substate, the term values were fitted to a Taylor-series expansion in powers of J(J + 1) to determine the substate origin energy and effective B-value. In this first phase of the study we did not attempt a full global fit to the assigned transitions, but instead fitted the sub-band J-independent origins to a restricted Hamiltonian containing the principal torsional and K-dependent terms. These included structural and torsional potential parameters plus quartic distortional and torsion–rotation interaction terms.

Random lasing from localized modes in strongly scattering systems consisting of macroporous titania monoliths infiltrated with dye solution

We have prepared random lasers that consist of macroporous titania monoliths infiltrated with dye solution and that operate close to light localization regime. When the excitation pulse energy exceeds a threshold, discrete spectral lines ascribed to laser oscillation appear on a featureless emission peak. No pulse-to-pulse variation was observed in the spectral positions of lasing lines, indicating that the lasing modes are localized in the medium. We demonstrated selective excitation of lasing modes by pumping at different positions on the sample.