Doppler Splitting Research Articles

Doppler splitting and expansion dynamics of laser-produced plasma plume under a high vacuum ambience

Doppler splitting appeared after the plume front passed because of the formation of the contact layer and quasi-cavity in the plasma plume and the movement of atoms in the lateral direction at a high vacuum.

The EDIBLES survey

Context. An unambiguous identification of the carriers of the diffuse interstellar bands (DIBs) would provide important clues to the life cycle of interstellar matter. The so-called C2-DIBs are a class of very weak bands that fall in the blue part of the optical spectrum and are associated with high column densities of the C2 molecule. DIB profile structures constrain potential molecular carriers, but their measurement requires high signal-to-noise, high-resolution spectra and the use of sightlines without Doppler splitting, as typical for a single-cloud situation. Aims. Spectra from the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) conducted at the Very Large Telescope (ESO/Paranal) were explored to identify single-cloud and high C2 column sightlines, extract the corresponding C2-DIBs and study their strengths and profiles, and to investigate in detail any sub-structures. Methods. The target selection was made based on profile-fitting of the 3303 and 5895 Å Na I doublets and the detection of C2 lines. The C2 (2–0) (8750–8849 Å) Phillips system was fitted using a physical model of the host cloud. C2 column densities, temperatures as well as gas densities were derived for each sightline. Results. Eighteen known C2-DIBs and eight strong non-C2 DIBs were extracted towards eight targets, comprising seven single-cloud and one multi-cloud line-of-sights. Correlational studies revealed a tight association of the former group with the C2 columns, whereas the non-C2 DIBs are primarily correlated with reddening. We report three new weak diffuse band candidates at 4737.5, 5547.4, and 5769.8 Å. We show for the first time that at least 14 C2-DIBs exhibit spectral sub-structures which are consistent with unresolved rotational branches of molecular carriers. The variability of their peak separations among the bands for a given sightline implies that their carriers are different molecules with quite different sizes. We also illustrate how profiles of the same DIB vary among targets and as a function of physical parameters, and provide tables defining the sub-structures to be compared with future models and experimental results.

Characteristics of laser-induced plasma under reduced background pressure with Doppler spectroscopy of excited atomic species near the shockwave front

We present measurements of Laser Induced Plasma expansion relying on classical, laterally resolved spectroscopy. Easy observable Doppler splitting of Cu I 324.75 nm spectral line provides measurement of radial expansion velocity in a straightforward way. The measurements are conducted in atmosphere of air, argon and hydrogen at low pressure in the range 20–200 Pa. We found that expansion velocity is linearly decreasing if pressure of surrounding gas increases, with velocity/pressure slope nearly the same for all three gases. Copper atoms have the highest expansion speed in argon ( ∼ 50 km/s) and the smallest speed in air ( ∼ 42 km/s). It is found that expansion velocity increases linearly with irradiance, while intensity of the spectral line is quite insensitive to the laser irradiance.

Doppler splitting generated by shock waves in laser induced breakdown spectroscopy

We present a classical spectroscopic approach for investigation of the fast plasma expansion present in Laser Induced Plasma. We show that characteristic form of the spectral lines, caused by significant Doppler effect, contains valuable information regarding the expansion velocity, plasma deceleration, emitters temperature, electron density and so on. The proposed numerical procedure is simple since the inverse Abel transform is not a necessary step. We illustrate this technique analyzing expansion of laser induced copper plasma in ambient gas at low (20Pa) pressure.

Doppler-shifted optical absorption characterization of plume-lateral expansion in laser ablation of a cerium target

The temporal evolution of the ablation plume of cerium was investigated by absorption spectroscopy. Cerium oxide pellets were ablated in a helium atmosphere by second-harmonic radiation (532 nm) from a Nd:YAG laser at a fluence of 0.5 J/cm2. The lateral velocity (expansion velocity horizontal to the sample surface) of the plume was determined from the magnitude of the Doppler splitting of the absorption spectra measured close to the sample surface. The lateral velocities of neutral and singly ionized atoms were systematically investigated by varying several parameters, such as ambient gas pressure, ablation laser fluence, observation timing, and observation height. In addition, temporal profiles of the absorption signal were measured by detuning the probe laser frequency from the atomic resonant frequency in order to obtain the temporal variation of the velocity. On the basis of the drag force model, the slowing coefficients for atomic and ionic species in a helium atmosphere were evaluated along with lateral velocity in a vacuum. This study may help in understanding the plume dynamics effect on deposited film properties as well as optimizing experimental conditions for ablation-based spectroscopic analysis.

Absorption spectroscopy of uranium plasma for remote isotope analysis of next-generation nuclear fuel

To determine experimental conditions suitable for isotope analysis, we studied the plume dynamics of uranium. A uranium oxide sample was ablated by 2nd harmonic radiation from a Nd:YAG laser at a fluence of 0.5 J/cm2. The temporal evolution of the ablation plume was investigated in vacuum and helium environments. In vacuum, the flow velocity perpendicular to the sample surface was determined to be 2.7 km/s for neutral atoms and 4.0 km/s for singly charged atoms. These velocities are about 20 % lower than those of cerium measured under similar conditions. From the evolution of the plume in helium, we found that an observation time of 3–5 μs and an observation height of about 2.5 mm are most suited for obtaining higher sensitivity. Observation times less than 3 μs were unsuitable for precise isotope analysis since the spectral modifications arising from the Doppler splitting effect are different between the two uranium isotopes. Using the established conditions, we evaluated the calibration curve linearity, limit of detection, and precision for three samples having different abundances of 235U.

A high-resolution survey of diffuse interstellar bands

This paper presents an atlas of diffuse interstellar bands together with tables with measurements of their parameters: central wavelengths, full widths at half-maximum and equivalent widths. For this goal the spectra of ten reddened, early-type stars have been selected. The spectra are of high resolution, ∼100 000, and reasonable signal-to-noise ratio, S/N > 300; they cover a wide spectral range 3500–10 000 A and show a lack of evident Doppler splitting in the interstellar K i line. The measurement technique has allowed a homogeneous set of data to be achieved. As a result, the identity of 336 DIBs from previous surveys has been confirmed and 21 new bands have been found. The spectral plots and the tables are available online.

Doppler measurement of implosion velocity in fastZ-pinch x-ray sources

The observation of Doppler splitting in K-shell x-ray lines emitted from optically thin dopants is used to infer implosion velocities of up to 70 cm/μs in wire-array and gas-puff Z pinches at drive currents of 15-20 MA. These data can benchmark numerical implosion models, which produce reasonable agreement with the measured velocity in the emitting region. Doppler splitting is obscured in lines with strong opacity, but red-shifted absorption produced by the cooler halo of material backlit by the hot core assembling on axis can be used to diagnose velocity in the trailing mass.

ELECTROMAGNETIC SCATTERING AND DOPPLER ANALYSIS OF THREE-DIMENSIONAL BREAKING WAVE CRESTS AT LOW-GRAZING ANGLES

The electromagnetic scattering of the synthesized three- dimensional (3-D) breaking wave crests which are formed by azimuthally aligning the individual 2-D breaking wave proflles has been numerically studied at the low-grazing angles (LGA) by using the multilevel fast multipole algorithm (MLFMA) with adaptive higher order hierarchical Legendre basis functions. Difierent from the specular (or quasi-specular) re∞ection and Bragg scattering, the \sea-spike phenomenon which is characterized by that horizontally polarization (HH) signals greatly exceed vertically polarization (V V ) signals has been demonstrated by analyzing both the backscattering of 3-D LONGTANK series and a plunging breaker. For the time- dependent evolution of the plunging breaker, the Doppler shifts and Doppler splitting efiects are investigated by applying the fast Fourier transform (FFT) with a moving Hamming window. The spectrum of HH scattering has the feature of concentration, while the spectrum of V V scattering shows the Doppler splitting efiects.

Doppler splitting in diffuse interstellar bands

We demonstrate evident Doppler splitting in the profiles of many narrow diffuse interstellar bands (DIBs). Their components are compared with those of atomic and molecular lines of interstellar origin. It is shown that it is likely that the species that shares both wavelength shifts and strength ratios of the Doppler components seen in the DIB profiles is the CH radical. Because of this profile resemblance, it is recommended that CH lines can be used to shift spectra to the rest velocity frame for interstellar features, especially to determine the DIB rest wavelengths on the basis of the CH line at 4300.3132 A in the spectrum of HD 147889. Our results strongly support a molecular origin of diffuse bands.

High‐Resolution Profiles of Diffuse Interstellar Bands

High-resolution (R = 115,000) echelle spectra (acquired with the ESO/HARPS spectrograph) of a few OB reddened stars, where no Doppler splitting is observed in interstellar atomic lines, are analyzed. The observed profile shapes allow us to divide the diffuse interstellar bands (DIBs) into several sets, characterized by very similar shapes and widths and thus likely carried by similar molecular species. However, not all DIBs behave in the same way; profiles of broader features remain unchanged (are difficult to divide into sets of similar shapes), while evident differences are seen in the narrow ones. Profiles of DIBs may change slightly from object to object, apparently due to different physical parameters in the intervening clouds; this supports the idea of their molecular origin. We also introduce a new parameter, which is a result of dividing the equivalent width of a diffuse band (in mÅ) by the depth of the feature (in percent). This parameter facilitates grouping of similar DIBs, as well as providing some quantitative information that allows us to estimate the broadness of a feature even for very complex profiles, vastly differing from Gaussian.

Fine structure in the profiles of strong diffuse interstellar bands

High-resolution echelle spectra of five reddened OB stars are used to analyse details of the profiles of diffuse interstellar bands (DIBs) at 4726, 4735, 5418, 5850, 6196, 6376, 6379 A together with the well studied 5797, 5780 and 6614 ones. All targets do not show Doppler splitting in the interstellar CH 4300 band with the applied resolving power R = 115 000. The profiles of DIBs differ from object to object except 5418 which looks invariant in our sample: the DIB is a good candidate for further study of possible isotopic effect. We also found that the width of bands at 5797 and 6614 A probably is more sensitive to the temperature (and density) effects than that of other DIBs in the sample, though almost all diffuse bands are narrowest in most ζ -type object (HD 179406) of the sample. On the other hand, it can be just peculiar effect as in a case of unusual line of sight HD 147889 which demonstrates very broad 5780 and 6614 A diffuse bands what hardly can be explained by temperature effects.

Electronic Doppler effect in resonant Auger decay of CO molecules upon excitation near a shake-upΠresonance

We present an experimental observation of the electronic Doppler effect in resonant Auger spectra upon core excitation slightly above the carbon K edge of the CO molecule. Thus the electronic Doppler effect has been identified in above-threshold excitation, and in a transition of Pi symmetry. Ab initio calculations of the potential energy curves of the relevant states of CO and the wave packet technique have been employed to provide a theoretical background to the experimental studies. The weak feature around 299.4 eV in the photoabsorption spectrum, whose decay has been investigated by the present experiment, is assigned to double (core-valence) excitations to C 1s shake-up states vertical bar 1s(C)(-1)1 pi(-1)pi(*2)> with a strong dissociative character, and the Doppler splitting of the atomic peak has been reproduced by the simulation.

A search for fine structure inside high resolution profiles of weak diffuse interstellar bands

This paper presents a survey of the high-resolution profiles of selected, moderately weak diffuse interstellar bands (DIBs) between 4725 and 6730 A. In very high signal-to-noise spectra, obtained as a result of averaging several individual exposures of reddened, early-type stars that show Doppler splitting of < 2k m s −1 in interstellar gas lines, the profiles seem to have a substructure. This supports the molecular origin hypothesis for DIBs. We studied the profiles of the diffuse interstellar bands at wavelengths of 4726.33, 4963.85, 5418.89, 5541.74, 5544.95, 5546.46, 5762.73, 5766.05, 5769.09, 6439.41, 6445.53, 6449.16, 6729.28 A.

Very high resolution profiles of four diffuse interstellar bands

Ultra-high-resolution (R ∼ 300 000) profiles of four diffuse interstellar bands (DIBs) are presented. The λλ 5797-, 5850-, 6196- and 6379- ˚ A DIBs were observed towards the reddened supergiant HD 24398, a line of sight free of Doppler splitting; thus the observed profiles can be considered as intrinsic to the DIB carriers. Three of the profiles show substructure which supports the hypothesis of a molecular origin for these DIBs.

Anisotropic Ultrafast Dissociation Probed by the Doppler Effect in Resonant Photoemission fromCF4

The resonant Auger spectrum from the decay of F 1s-excited CF4 is measured. Several lines exhibit a nondispersive kinetic energy as the exciting photon energy is tuned through the resonance region. The F 1s(-1) atomiclike Auger line is split into two components due to the emission of Auger electrons by a fragment in motion, when electron emission is observed along the polarization vector of the light. This Doppler splitting is direct evidence that the core excitation leads to T(d)-->C(3v) symmetry lowering, by elongation of a specific C-F bond preferentially aligned along the polarization vector of the incident photon.

The Doppler effect in NMR spectroscopy

An NMR sample may be subject to motions, such as those due to sample spinning or to liquid flow. Is the spectrum of such a sample affected by the Doppler effect? The question arises because, instrumental dimensions being much shorter than the wavelength, it is the near-field of the precessing magnetic moment which couples to the receiver coil, rather than the radiated far-field. We expand the near-field into plane propagating waves. For each such wave there is another one with the same amplitude, propagating in the opposite direction. The Doppler shifts are therefore equal and opposite. In the model case of a small fluid sample moving with constant velocity, this leads to a distribution of Doppler shifts which is symmetrical with respect to the unshifted frequency: there is no net spectral shift. We examine the possibility of observing the Doppler distribution in this case. We also consider the case of thermal motion of a gas. We draw attention to the resolved Doppler splitting of molecular rotational transitions in a supersonic burst as observed in a microwave resonator. We also mention briefly the Doppler effect in molecular beam spectroscopy.

Very high resolution profiles of 6196 Å and 6614 Å diffuse interstellar bands

We present a careful analysis of very high resolution (R = 220000) profiles of two well correlated diffuse interstellar bands (DIBs): 6196 and 6614 A observed along 7 lines of sight free of the Doppler splitting in interstellar atomic lines. The high signal-to-noise ratio (S/N) of the spectra (∼600-1000) allows us to draw definite conclusion that the ratio of equivalent widths of the two DIBs is not always exactly the same, i.e. they do not seem to originate at the same carrier. The DIB profiles vary from object to object but the variations are different for every DIB. The width of 6196 DIB may change by up to 1.5 times lowest value while that of 6614 remains almost constant. The broadening of 6196 is not caused by the Doppler splitting, absent in atomic interstellar lines. Possibly this fact reflects a strong dependence of the carrier excitation pattern on small variations of physical parameters. The variations of substructure strength ratios inside the 6614 DIB profile, evident in our spectra, are apparently caused by a mechanism different from that which broadens DIB 6196.

The dynamic Auger–Doppler effect in HF and DF: control of fragment velocities in femtosecond dissociation through photon energy detuning

The Auger–Doppler effect in the experimental spectra of HF and DF is presented, and the dynamics of ultra-fast dissociation in the core-excited state are discussed. The Doppler splitting of the atomic Auger peak is calculated and simulated using a classical model and a very good agreement is found between experiment and simulation. It is shown that the difference in photon energy relative to the resonance is transferred completely into the kinetic energy release (KER). This is expected to be a general phenomenon, but is clearly illuminated in the HF/DF case. Thus the fragment velocity can be controlled through photon energy detuning.

Intrinsic Profiles of Strong Diffuse Interstellar Bands

This paper presents a survey of the profiles of strong diffuse bands based on an extensive set of high-resolution spectra acquired with the echelle spectrograph installed at the Cassegrain focus of the 2.1 m telescope of the McDonald Observatory. Only targets characterized by narrow and symmetric lines of interstellar sodium, as well as by very high signal-to-noise ratio (S/N), have been selected. The surveyed diffuse interstellar bands are those at 5780, 5797, 5850, 6196, 6234, 6270, 6376, 6379, 6614, and 6660 A. The possible modifications caused by stellar and telluric lines, as well as by Doppler splitting, are discussed together with methods of getting rid of them. The presented profiles are as free of the aforementioned contaminations as possible. The very broad features such as λ5778 and λ6177 are not discussed, as their profiles extracted from the echelle spectra are very uncertain. The λ6203/λ6205 feature is also not considered, as it is a mixture of two unresolvable diffuse bands of different origin. The very broad 6284 A band is so contaminated with telluric features that its profile was also found to be too uncertain. The spectra are still not of high enough S/N to discuss the profiles of the numerous weak interstellar features discovered recently.