Line Profile Measurements Research Articles

Texture versus Residual Deformation Effects in Metal Materials: Principles of Experimental Approach and General Regularities

For systematic study of the distribution of residual deformation effects in textured metal materials the method of Generalized Pole Figures was developed, combining texture measurement with X-ray line profile measurements in such a manner that the profile of the same X-ray line (hkl) is registered by each successive position of the sample. The obtained totality of profiles after that or another treatment is used for construction of Generalized Pole Figures (GPF), i.e. distributions of measured diffraction parameters or calculated substructure parameters in the stereographic projection of the sample depending on the orientation of reflecting crystallographic planes. As applied to metal materials with developed rolling textures it was found that any volume ~1 mm3 is characterized by an extremely wide spectrum of substructure conditions. Three laws of substructure anisotropy were revealed for the first time. The 1st law: Residual deformation effects are minimal along directions, corresponding to maximal density of crystallographic axes, i.e. texture maxima, and increase up to highest values by passing to texture minima. The 2nd law concerns variation of lattice parameters in metal products due to elastic microstrain: For each grain with crystalline lattice, extended along axis <hkl> by (+ε), there is its pair with the symmetric orientation, where along axis <hkl> crystalline lattice is compressed by (-ε), so that accompanying elastic microstresses are equilibrated. The 3rd law: By passing from residual tension of the crystalline lattice to its compression, grain fragmentation changes depending on indexes of the reference axis, i.e. tensile and compressive elastic deformations of the crystalline lattice differ in their uniformity.

Precise determination of the Doppler width of a rovibrational absorption line using a comb-locked diode laser

Abstract We had reported in a previous paper the precision measurement of line profiles of a transition of 13 C acetylene in the near-infrared region, employing a tunable diode-laser spectrometer, the frequency of which is locked to an optical-comb signal [K.M.T. Yamada et al., J. Mol. Spectrosc. 249 (2008) 95–99]. In the present article we review the methodology for the experiment and the analysis in determining the Boltzmann constant from the Doppler width of a rovibrational transition on the basis of our experiences. Problems to be surmounted for further improvement in accuracy are discussed. To cite this article: K.M.T. Yamada et al., C. R. Physique 10 (2009).

Precise measurements of spectral line profiles

We present a method of precise measurements of spectral line profiles that was elaborated and tested on the Main Stellar Spectrograph (MSS) of the 6-m BTA telescope. The method allows discarding corrections for flat field. To take account of inhomogeneity of the CCD chip sensitivity, two spectra are recorded, shifted against each other along the dispersion by one column. Recurrent ratios between the photo responses of the CCD pixels let us determine their relative sensitivity and correct the line profiles. To eliminate various instability effects, the spectra are registered with the use of a cyclic shift procedure along the dispersion, and a synchronous electronic image transfer across the spectrum dispersion (along the CCD matrix columns).

Semiempirical model for analysis of inhomogeneous optically thick laser-induced plasmas

In this paper, a more realistic approach of a non-uniform optically thick plasma in local thermodynamic equilibrium was applied to describe self-reversal of Co I 340.51 nm emission line recorded from a laser-induced plasma generated on a Co–Cr–Mo metallic alloy. This line was selected because it is one of the most absorbed of the major elements in air at atmospheric pressure. The model describes the behavior of the plasma after the breakdown, and it was semiempirical thus, some information was taken from the experiment. A cylinder-symmetrical plasma column with a parabolic temperature distribution having a maximum at the center and decreasing toward the edges was considered. The input parameters were the plasma length, the temperature in the plasma core, and the Co total density, which were estimated from measurements and previous work. Moreover, the distribution of electron density depended on the temperature, and the ionization degree was taken into account through Saha equation. Then, plasma parameters were adjusted in such a way calculations reproduced the experimentally measured line profiles. The effect of varying laser power on plasma homogeneity and its evolution in time were investigated. Moreover, preliminary results of spatial distribution of plasma parameters were obtained that confirmed the practical application of the model on plasma diagnostics.

Development of soft X-ray multilayer laminar-type plane gratings and varied-line-spacing spherical grating for flat-field spectrograph in the 1–8 keV region

W/C and Co/SiO 2 multilayer laminar-type holographic plane gratings (groove density 1/σ = 1200 lines/mm) in the 1–8 keV region are developed. For the Co/SiO 2 grating the diffraction efficiencies of 0.41 and 0.47 at 4 and 6 keV, respectively, and for the W/C grating 0.38 at 8 keV are observed. Taking advantage of the outstanding high diffraction efficiencies into practical soft X-ray spectrographs a Mo/SiO 2 multilayer varied-line-spacing (VLS) laminar-type spherical grating (1/σ = 2400 lines/mm) is also developed for use with a flat field spectrograph in the region of 1.7 keV. For the Mo/SiO 2 multilayer grating the diffraction efficiencies of 0.05–0.20 at 0.9–1.8 keV are observed. The FWHMs of the measured line profiles of Hf-Mα 1(1644.6 eV), Si-Kα 1(1740.0 eV), and W-Mα 1 (1775.4 eV) are 13.7 eV, 8.0 eV, and 8.7 eV, respectively.

Long-range internal stresses in monotonically and cyclically deformed metallic single crystals

Abstract Selected experimental measurements and theoretical predictions for the magnitude of long-range internal stress in monotonically and cyclically deformed metals are assessed and recently developed, spatially-resolved X-ray micro-beam techniques for direct measurements of long-range internal stress are discussed. The results of previously reported differential-aperture X-ray microscopy spatially-resolved measurements of long-range internal stress in dislocation-cell interiors in monotonically deformed copper are compared with predictions and analyses associated with the composite model of deformation. In addition, the results of volume-integrating X-ray line-profile measurements and spatially-resolved differential-aperture X-ray microscopy measurements of strains in <100> oriented copper single crystals that were cyclically deformed to pre-saturation (without persistent slip bands) are presented.

Monte Carlo simulation for excessive Balmer line broadening generated by transport of fast H Atoms in an abnormal glow discharge

Monte Carlo code for fast hydrogen atom transport and generating of excessively Doppler broadened profiles based on the collision model is presented. Results for the initial monoenergetic atom beam and for a more realistic energy distribution of H atoms are reported. Line profiles obtained from the simulation are compared to our experimentally obtained data. Initial energy distribution for atoms is approximately calculated from the measured line profiles while the initial angle distribution was taken to be cosine. Balmer alpha intensity was found to exponentially decay in the negative glow region, which concurs with the experimental results. These agreements between the simulation and experiment support the collision model for excessive line broadening.

Interpretation of Solar Magnetic Field Strength Observations

This study based on longitudinal Zeeman effect magnetograms and spectral line scans investigates the dependence of solar surface magnetic fields on the spectral line used and the way the line is sampled to estimate the magnetic flux emerging above the solar atmosphere and penetrating to the corona from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO). We have compared the synoptic program λ5250 A line of Fe i to the line of Fe i at λ5233 A since this latter line has a broad shape with a profile that is nearly linear over a large portion of its wings. The present study uses five pairs of sampling points on the λ5233 A line. Line profile observations show that the determination of the field strength from the Stokes V parameter or from line bisectors in the circularly polarized line profiles lead to similar dependencies on the spectral sampling of the lines, with the bisector method being the less sensitive. We recommend adoption of the field determined with the line bisector method as the best estimate of the emergent photospheric flux and further recommend the use of a sampling point as close to the line core as is practical. The combination of the line profile measurements and the cross-correlation of fields measured simultaneously with λ5250 A and λ5233 A yields a formula for the scale factor δ −1 that multiplies the MWO synoptic magnetic fields. By using ρ as the center-to-limb angle (CLA), a fit to this scale factor is δ −1=4.15−2.82sin 2(ρ). Previously δ −1=4.5−2.5sin 2(ρ) had been used. The new calibration shows that magnetic fields measured by the MDI system on the SOHO spacecraft are equal to 0.619±0.018 times the true value at a center-to-limb position 30°. Berger and Lites (2003, Solar Phys. 213, 213) found this factor to be 0.64±0.013 based on a comparison using the Advanced Stokes Polarimeter.

Absolute Line Profile Measurements of Silicon Plane Mirrors by Near-Infrared Interferometry

Absolute line profiles of three silicon plane mirrors were measured by the three-flat method using a near-infrared interferometer. The interferometer was constructed using a near-infrared laser diode with 1310 nm wavelength light, to which the silicon plane mirror is transparent. The maximum height difference in the absolute line profiles is less than 8.9 nm and the rms value of height difference is less than 2.0 nm for a measured line of 12.7 mm. The near-infrared interferometer is useful for measuring a set of line profiles at the height difference level to calculate the absolute flatness of silicon plane mirrors.

Stark broadening in the Sb III spectrum

The shapes of nine doubly ionized antimony (Sb III) spectral lines have been obtained in the laboratory helium plasma at 17 500 K electron temperature and electron density of 9.4 × 10 22 m −3 . Measured line profiles are of a Voigt type. At the mentioned plasma conditions the Stark broadening has been found as the dominant mechanism in the Sb III line shapes formation. Using a deconvolution procedure the Lorentz (Stark) FWHM (Full-Width at Half of the Maximal intensity, W) have been obtained. Our measured Sb III Stark widths are the first data in the literature. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in helium with antimony atoms, as impurities. They were evaporated from the thin antimony layer, deposited on the silver cylindrical plates, located in the homogenous part of the discharge. This plasma source ensures good conditions for the generation of the doubly ionized antimony atoms in the helium plasma due to atomic processes concerning helium metastables.

Nonsingular dislocation and crack fields: implications to small volumes

The simplest, yet robust, gradient elasticity theory (GRADELA) as first introduced by the last author is used to deduce nonsingular expressions for the stress and strain fields near dislocation lines and crack tips. These expressions are particularly useful for small volumes where the details of the deformation field need to be known for interpreting related experimental observations. Various implications are discussed in relation to the determination of the size of dislocation cores, the size of maximum stress or maximum strain in crack tips, and the interpretation of X-ray line profile measurements in determining internal stresses.

Spatial and temporal probing of a laser-induced plasma plume by cavity ringdown spectroscopy

The laser-induced plasma plume of a Ti target in vacuum is probed by the technique of cavity ringdown spectroscopy. A model is developed to perform a forward convolution of atomic absorption line profile measurements. The model accounts for laser-induced plasma characteristics such as anisotropy of the plume and velocity distributions of the ablated particles as well as of the cavity ringdown features such as geometry and time selectivity. The absorption lineshapes of atomic transitions are calculated and discussed for given sets of parameters. Calculated line profiles are fitted to experimental line profiles obtained from nanosecond-laser ablation of the target and provide data about the plume dynamics.

ROTATIONAL VELOCITIES FOR EARLY-TYPE STARS IN THE YOUNG LARGE MAGELLANIC CLOUD CLUSTER R136: FURTHER STUDY OF THE RELATIONSHIP BETWEEN ROTATION SPEED AND DENSITY IN STAR-FORMING REGIONS

We present the results of a study aimed at assessing the distribution of rotation speeds, N(v sin i) among O- and early B-type stars located in R136, a young (t ~ 1-4 Myr) cluster in the Large Magellanic Cloud (LMC) characterized by a stellar density at least three times that of the densest Galactic clusters in which stellar rotational velocities have been measured. Our goals are (1) to determine whether the distribution of N(v sin i) in R136 shows the same paucity of slowly rotating stars and high mean rotation speed that distinguish early-type stars located in bound clusters in the Milky Way Galaxy (MWG) from their analogs among members of the field and unbound associations and (2) to determine whether the mean rotation speed in the extremely dense R136 cluster is even higher than the values measured for lower-density bound clusters. Our data comprise vsin i estimates for 24 stars obtained by comparing line profile measurements obtained with the Gemini Multi-Object Spectograph on the Gemini South Telescope with a grid of He I and He II line profiles generated from model atmospheres and broadened to emulate the effects of stellar rotation. We find that for R136, 13 stars with masses in the range 6-12 M ☉ have an average apparent rotational velocity of vsin i = 233 ± 19 km s–1; by comparison, for LMC stars in this same mass range in the field and in lower-density clusters, vsin i is, respectively, 105 ± 8 km s–1 and 147 ± 14 km s–1. For 11 15-30 M ☉ stars in R136, vsin i = 189 ± 23 km s–1; by comparison, the LMC stars in this same mass range but drawn from lower-density regions have vsin i = 129 ± 13 km s–1. Moreover, we find that throughout this entire mass range, R136 lacks the cohort of slow rotators characteristic of early-type field stars, both in the LMC and in the MWG. We provide arguments that these differences in N(v sin i) are unlikely to arise from evolution-driven changes in angular momentum (e.g., angular momentum loss through stellar winds), but rather may reflect differences in the rotation speeds imprinted at the time the stars formed. This result appears most certain for stars with masses in the range 6-12 M ☉; for stars of higher masses, larger samples from regions of differing densities are needed to more firmly establish that the observed differences are imprinted during the stellar assembly phase as opposed to being the result of subsequent evolution. We further argue that the differences in N(v sin i) between R136 and the LMC and MWG field stars likely result from a difference in the initial conditions in protostellar cores that are found in the types of molecular cloud regions that form rich, dense clusters (e.g., higher turbulent speeds) rather than from differences in the environment surrounding the core (e.g., stellar density, UV radiation field).

Development of Surface Hall Potentiometry to Reveal the Variation of Drift Velocity of Carriers in Semiconductor Materials

Surface Hall potentiometry is a method of detecting the Hall effect occurring in a semiconductor material as the surface potentials change. An experimental setup to detect surface Hall potentials by the Kelvin method is introduced. After we reveal the basic characteristics of surface Hall potentials, a silicon sample is prepared to induce the variation of the drift velocity of carriers. Line-profile measurements of surface Hall potentials with this sample demonstrate that our method reveals the distribution of drift velocities of carriers in semiconductors, which reflects electronic or structural properties such as the carrier type (hole or electron), current density, and thickness.

High precision line profile measurements on 13C acetylene using a near infrared frequency comb spectrometer

Line profiles of a rovibrational transition of 13C acetylene have been measured for various pressures in the near infrared region. In order to accomplish high precision in frequency, we have employed a diode-laser, the frequency of which is locked to an optical comb. By tuning the comb frequency we have achieved a continuous frequency tuning over 2 GHz for the measurement of Doppler broadened line profiles spread over 2 GHz. In addition we have stabilized the incident power of the laser on the sample cell by adjusting the gain of a fiber amplifier via a feed-back loop. Observed profile data have been analyzed by the generalized Voigt function to determine the Gaussian width precisely: at the present we realized a precision of 10 - 3 . The zero pressure line center position was determined with a precision of 10 - 9 .

Resonant fluorescence line narrowing and gain spectral hole burning in erbium-doped fiber amplifier

Gain spectral hole burning and resonant fluorescence line narrowing have been performed at low temperature in standard aluminosilicate erbium-doped fiber amplifier to demonstrate the nature of the line broadening. Comparison of the hole-width measurements with resonant fluorescent line narrowing data shows a good agreement at 77 K, working temperature for which both experiments are feasible and have been performed simultaneously. The FWHM results reported here compare well with the earlier line profile measurements performed on aluminosilicate glass preform of the same chemical composition as the fiber. The pump power dependences are reported and indicate that they influence both the depth and line width, which may induce a limitation for wavelength division multiplexing techniques in the long-haul transmission regime of telecommunications.

Fabry–Pérot lineshape analysis in an optically thick expanding plasma

In this work the authors present Fabry–Pérot measurements of Ar atom spectral line profiles originating from the expansion of an Ar–N2 thermal plasma into a low pressure environment. The plasma is characterized by strong density, temperature and velocity gradients and it offers a high degree of light absorption for some gas mixtures. First, it is demonstrated that the Abel inversion method cannot be applied under such conditions even if absorption is absent. Second, two approaches are examined to obtain plasma parameters in the case of an optically thick expanding plasma. It is shown that velocity and temperature development along the jet radius can be inferred from experimental lineshapes when radiation production and absorption are taken into account in the core and in the surroundings of the jet.

RBS1423 – a new QSO with relativistic reflection from an ionised disk

We present the analysis and results of a 20 ks XMM-Newton observation of RBS1423. X-ray spectral analysis is used to establish a significantly broadened relativistic iron K-alpha line from a highly ionised disk. A QSO at z=2.262 was considered to be the optical counterpart of this ROSAT Bright Survey X-ray source. Based on the improved XMM-Newton source position we identified a z=0.208 QSO as optical counterpart to RBS1423. The 0.2-12 keV X-ray luminosity of this radio-quiet QSO is 6x10^{44} erg/s. The XMM-EPIC spectra are well described by a power law with a significantly broadened iron K-alpha line. Disk line models for both Schwarzschild and Kerr black holes require hydrogen-like iron ions to fit the measured line profile. Significant ionisation of the reflection disk is confirmed by model fits with ionised disk models, resulting in an ionisation parameter xi~2000.

The dynamics of the minimum solar corona during the period August–October 1996

The paper presents the dynamics of the solar corona at the minimum phase of the solar cycle (period August–October 1996), as inferred from LASCO-C1 spectral data. LASCO-C1 is an internally occulted coronagraph aboard the SOHO spacecraft. It has a tunable Fabry–Pérot interferometer which allows taking spectral scans of selected coronal emission lines. From measured line profiles we deduced physical quantities such as temperature and flow velocities along the line of sight. This way, we obtained information on the flow pattern in the low corona (1.1–1.6 solar radii).

Microstructure of crystalline materials determined by whole powder pattern X-ray line profile analysis

Powder diffraction patterns consisting of broadened line profiles are used to evaluate microstructure parameters. The microstructure is modelled in terms of crystallite size and microstrain, where microstrain is assumed to be caused by dislocations, triple junctions corresponding to sinter stresses, and to some extent, by planar defects, especially stacking faults and twin boundaries. Crystallite size needs special interpretation, in the case of ceramic powders it is often identical to the particle or grain size, whereas in the case of bulk materials, especially bulk metals or alloys it is equal to the subgrain size. Electron microscopy strongly facilitates the appropriate interpretation of X-ray crystallite size. The diffraction patterns are evaluated by the method of convolutional multiple whole profile (CMWP) fitting procedure [1,2]. In this procedure strain and size is modelled by dislocations and spherical or ellipsoidal crystallites with log-normal size distributions, respectively. The model generated and the measured diffraction patterns are compared by a nonlinear least squares method, in a similar way as in the whole powder pattern modelling (WPPM) method [3]. The effect of stacking faults and twins on X-ray diffraction patterns has been calculated numerically by using the DIFFaX [4] software for the first 15 Bragg reflections in fcc crystals up to 20 % fault densities [5]. It is found that the Bragg reflections consist of 5 types of sub-reflections which are of Lorentzian type. About 15.000 sub-reflections are evaluated and parametrized according to their FWHM and positions relative to the exact Bragg angles. These parameter files are incorporated into the CMWP software for evaluating planar faults together with dislocations and crystallite and/or sub-grain size distributions [5]. In nanocrystalline Cu and Cu-Zn alloys it has been found that twinning becomes a substantial mode of deformation when the grain size is smaller than about 40 and 60 nm, respectively. An unusual behaviour of line broadening in ball milled fluorides has been observed [6]. About twenty diffraction patterns corresponding to different ball milled states of the CaF 2, SrF2, BaF2 and CdF2 fluorides have been analysed in terms of dislocation densities and types, and crystallite size and size distributions by X-ray line profile analysis [6]. The diffraction patterns have been evaluated by the method of convolutional multiple whole profile (CMWP) fitting procedure [2,3]. In about 10 of the 20 patterns the calculated and measured diffraction patterns are in perfect agreement throughout the entire angular range of measurement. However, in the cases of the rest of the patterns the first few measured line profiles appear to be narrower than the calculated profiles based on the model. Nevertheless, also in these latter cases the measured and calculated patterns are in perfect agreement for the higher angular parts of the patterns consisting of 10 to 13 profiles. In the cases where this discrepancy is present, it is interpreted as an X-ray optical interference effect [6] similar to what has been observed by Rafaja et al. [7] in nanocrystalline thin layers. The interference effect has been corrected successfully, either by (i) excluding the affected profiles from the evaluation procedure or by (ii) assuming a diffraction angle dependent apparent bimodal size distribution of crystallites [6].