Showing papers on "Doppler broadening published in 1994"
TL;DR: An optical magnetometer based on atomic coherence effects is analyzed using a quantum Langevin approach and effects of Doppler broadening and fluctuations of the driving field are discussed and a comparison to standard optical-pumping magnetometers is made.
Abstract: An optical magnetometer based on atomic coherence effects is analyzed using a quantum Langevin approach. The large dispersion of a phase-coherent atomic medium (``phaseonium'') at a point of vanishing absorption is used to detect magnetic level shifts via optical phase measurements in a Mach-Zehnder interferometer with sensitivities potentially superior to state-of-the-art devices. Effects of Doppler broadening and fluctuations of the driving field are discussed and a comparison to standard optical-pumping magnetometers is made.
119 citations
01 Oct 1994-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a modification to the general-purpose Monte Carlo electron-photon transport code EGS4 was made in order to include Doppler broadening of Compton-scattered photon energy due to electron pre-collision motion.
Abstract: A modification to the general-purpose Monte Carlo electron-photon transport code EGS4 [1] was made in order to include Doppler broadening of Compton-scattered photon energy due to electron pre-collision motion. The Compton-scattered photon energy is sampled from a cross section formula based on the Compton profile, and the Compton scattering is sustained if the energy imparted to the electron is less than its binding energy. The electron binding effect modifies the scattered photon energy, angular distribution, and total cross section of the Compton scattering, and affects the photon mean free path used in the calculations. In the improved EGS4 code, all of these electron binding effects in Compton scattering are treated consistently. A simulation of 40 keV photon scattering by C and Cu samples was performed using the improved EGS4 code; the calculated scattered photon spectra agreed well with the measurements.
103 citations
TL;DR: The threshold at which self-focusing initially dominates the dynamics of short-pulse propagation in normally dispersive bulk media, causing an explosive increase in peak intensity, is estimated analytically and verified numerically.
Abstract: The threshold at which self-focusing initially dominates the dynamics of short-pulse propagation in normally dispersive bulk media, causing an explosive increase in peak intensity, is estimated analytically and verified numerically. Intensity-dependent propagation effects such as spectral broadening also occur explosively at this threshold.
90 citations
TL;DR: The nonlinear Schrödinger equation predicts conical emission that is due to spatiotemporal propagation of short pulses in normally dispersive, cubically nonlinear media.
Abstract: The nonlinear Schrodinger equation predicts conical emission that is due to spatiotemporal propagation of short pulses in normally dispersive, cubically nonlinear media. This effect is a direct consequence of a four-wave interaction.
90 citations
TL;DR: In this paper, the scattering rates are computed self-consistently accounting for the spectral broadening of the electronic spectra due to a finite energy level lifetime, which may explain the absence of a significant reduction in quantum dot luminescence compared with that from quantum wells.
Abstract: Luminescence efficiency in quantum dots has been a matter of some controversy recently. Theoretically, poor efficiency has been predicted owing to the phonon bottleneck in carrier relaxation, while slightly enhanced luminescence has been reported in several experiments. The approach of this letter differs from previous theoretical work in that the scattering rates are computed self‐consistently accounting for the spectral broadening of the electronic spectra due to a finite energy level lifetime. Scattering of electrons and holes confined in the dot is found to be responsible for breaking the phonon bottleneck in electron relaxation reducing the relaxation time from several ns to several hundred ps. Results of a Monte Carlo simulation also including confined and interface polar optical phonon and acoustic phonon scattering for a range of quantum dot dimensions and temperatures are presented. These results may provide an explanation of the absence of a significant reduction in quantum dot luminescence compared with that from quantum wells.
59 citations
TL;DR: In this paper, the fast dynamics of the oxazine dye LD690 in a series of n-alcohols were investigated using several techniques, including linear absorption, resonance Raman, and the femtosecond three-pulse photon echo.
54 citations
TL;DR: In this paper, the excitation spectrum of the L 3 -M 5 X-ray emission of Dy compounds in the pre-edge region of Dy L 3 Xray absorption near edge structure (L 3 -XANES) is theoretically investigated based upon the coherent second order optical formula with multiplet coupling effects.
Abstract: The excitation spectrum of the L 3 -M 5 X-ray emission of Dy compounds in the pre-edge region of Dy L 3 X-ray absorption near edge structure (L 3 -XANES) is theoretically investigated based upon the coherent second order optical formula with multiplet coupling effects. The spectral broadening of the excitation spectrum is determined by the M 5 core hole lifetime, being free from the L 3 core hole lifetime. The fine pre-edge structure of the L 3 edge due to the 2 p →4 f quadrupole transition can be seen in the excitation spectrum, while this structure is invisible in the conventional XANES, in agreement with the recent experimental results. We clarify the conditions for the excitation spectrum to be regarded as the absorption spectrum with a smaller width. The resonant X-ray emission spectra for various incident photon energies around the L 3 edge are also calculated.
53 citations
TL;DR: In this paper, a semi-empirical model was proposed to calculate positron states and annihilation rates for nine different II-VI compound semiconductors, based on the local density approximation (LDA) for the electron-positron correlation effects.
Abstract: Positron states and annihilation rates are calculated for nine different II-VI compound semiconductors. Positron annihilation from the delocalized states in the perfect lattice as well as from the localized states at vacancies and divacancies is considered. The calculations are based on the local-density approximation (LDA) for the electron-positron correlation effects. The calculations are performed using non-self-consistent electron densities and electrostatic potentials obtained by atomic superposition and solving for the three-dimensional positron wavefunctions by a relaxation method. For the perfect lattices, also self-consistent electron densities and positron states (linear muffin-tin orbital method within atomic-spheres approximation, LMTO-ASA) are calculated. The results show that positron annihilation with the outer d electrons of the group II metal atoms plays an important role. The positron lifetimes calculated for perfect lattices are a few per cent shorter than the experimental ones, indicating an LDA overestimation of the d-electron enhancement around the positron. These bulk lifetimes can be corrected efficiently by a semiempirical model introduced in this work. In the case of positrons trapped by defects, the present theoretical description is less satisfactory, because atomic relaxations due neither to rearrangements in the electronic structure nor to the localized positron are taken into account. However, the calculated annihilation probabilities with core and valence electrons will serve as an important database for methods in which defects can be identified using the positron angular correlation or Doppler broadening measurements.
52 citations
TL;DR: In this paper, backscatter emission of mesospheric sodium atoms in a laser guide star that is excited by pulses ranging from 30-ns to 0.9-μs duration is described.
Abstract: Calculations of backscatter emission of mesospheric sodium atoms in a laser guide star that is excited by pulses ranging from 30-ns to 0.9-μs duration are described. The efficient use of such pulses at saturating irradiance values is shown to require ~3 GHz of spectral broadening to provide access to the full absorption spectrum of the D2 line. The broadening is provided by frequency modulation. A set of density matrices was used to account for all 24 hyperfine states and inhomogeneous Doppler broadening. At the broadband (3-GHz) saturation irradiance of 4 W/cm2, both linearly and circularly polarized laser beams are shown to produce emission rates exceeding 60% of the maximum possible rate-equation rate for the 0.9-μs pulses. As expected, circular polarization produced more backscatter than did linear polarization, but the enhancement never exceeded 1/3 in the calculations that are reported. A brief estimate of state precession in the Earth’s magnetic field suggests that achieving even this enhancement will require that the time scale for optical pumping be held to less than 1 μs, which will require the use of irradiances greater than 0.7 W/cm2 and spectral coverage of the full 3-GHz hyperfine-plus-Doppler absorption profile, at least until most of the population is pumped out of the F = 1 ground states.
50 citations
TL;DR: In this article, the second-harmonic generation (SHG) and Raman spectroscopy have been applied to investigate surface strain/stress appearing at the interface between Si(111) and thermally grown SiO2 layers.
Abstract: Optical second-harmonic generation (SHG) and Raman spectroscopy have been applied to investigate surface strain/stress appearing at the interface between Si(111) and thermally grown SiO2 layers. From the frequency shift and spectral broadening of the optical phonon mode of Si(111) covered by a 608-A-thick oxide layer, a tensile stress of 19 kbar was obtained. The azimuthal distribution of the reflected second-harmonic (SH) signal varies with the thickness of surface oxide. To deduce the strain in the lattice-deformed layer, a simple microscopic theory based upon the bond additivity model was proposed, and an agreement between the results of SHG and Raman spectroscopy was achieved. This study suggests that SHG is a sensitive technique for examining surface stress/strain between two lattice-mismatched layers. Therefore it can be useful for the study of the structure of Si1-x Gex and many other strained-layer systems.
49 citations
TL;DR: In this article, a three-grid mass gate is used to select only the desired cluster, 56FeC2- and 56FeH2H-, to enter the PES interaction zone.
Abstract: delivered by two pulsed molecular beam valves (R. M. Jordan Co.) and is synchronized with the vaporization laser pulse. The plasma reactions of CHq and Fe produce a variety of cluster species which, together with the He carrier gas, undergo a supersonic expansion and are skimmed twice to form a collimated beam. FeC2- and FeC2H- are the smallest Fecontaining anions, and the FeC2- signal is quite weak. FeC2H2is also present, but its abundance is rather weak and unstable. About 70 cm downstream from the cluster nozzle, the negative ion species are extracted by a 1 kV high-voltage pulse into a 130 cm long flight tube for mass analyses. The TOF mass spectrometer has a large extraction volume and a modified Wiley-McLaren extraction stack with an added free-flight region between the two acceleration stages? Theoretically, a very high mass resolution can be achieved in this setup with the large extraction volume. We have obtained a mass resolution (MI AM) of more than 300, sufficient to resolve all the isotopic species pertinent to the present study. A three-grid mass gate is used to select only the desired cluster, 56FeC2- and 56FeC2H-, to enter the PES interaction zone. The 56FeC2H- ions can be mass-gated cleanly while the 56FeC2signal may be contaminated by a negligible amount of %FeC2H2-. The mass-selected cluster packet is decelerated by a new momentum deceleration procedure7 down to a very low velocity before photodetachment. This minimizes the Doppler broadening on the photoelectron kinetic energy distribution, a crucial step in achieving high-energy resolution with the magnetic bottle-type analyzer. The third harmonic of a second Qswitched Nd:YAG laser is used in the current study for the photodetachment. There is a cutoff for the transmission of lowenergy electrons at about 0.4 eV. The spectrometer is calibrated with the known spectrum of Cu-. The energy resolution (AE) in a TOF spectrometer is not constant with respect to the electron kinetic energy (Ek). AE is proportional to Ek3/2. An energy resolution of 30 meV at 1 eV electron kinetic energy is achieved in the current spectrometer with the new deceleration procedure, as measured from the photoelectron spectrum of Cu- at 3.49 eV photon energy. This resolution is no longer limited by the Doppler broadening. When the ion signal is weak, full deceleration cannot be achieved to reach this resolution.
TL;DR: In this article, it is shown that Doppler broadening measurements on singlet, doublet and triplet emission spectra from the following impurity ions found in the boundary layer of the TEXTOR tokamak: Cii, Ciii, Civ, Siii, and Siiii.
Abstract: Examples are presented of Doppler broadening measurements on singlet, doublet and triplet emission spectra from the following impurity ions found in the boundary layer of the TEXTOR tokamak: Cii, Ciii, Civ, Siii, and Siiii. The shapes of these spectral lines are significantly influenced by the confining magnetic field of some 2T, in some cases exhibiting an appreciable Paschen-Back effect which complicates their appearance. It is shown that reliable values for the particular ion temperature can be obtained from the Doppler widths of the various Zeeman components, when the presence of the magnetic field is properly accounted for. Such temperatures derived from partially ionised impurity species should, however, be cautiously interpreted, as the ions in question probably do not exist for long enough in the particular ionisation stage to achieve thermal equilibrium with the background deuterons and protons. This interpretation of our results is supported by a simple one-dimensional model of ionisation and collisional heating processes in the plasma boundary.
TL;DR: In this article, the authors studied the field-induced broadening of optical absorption in InP-based quantum well (QW) structures with both strong and weak quantum confinement and showed that the spectral broadening associated with the applied electric fields is largely due to the quantum confinement of the barrier structures.
Abstract: We have studied in detail the field‐induced broadening of optical absorption in InP‐based quantum well (QW) structures with both strong and weak quantum confinement. Electroabsorption process in the QW structures with the weak confinement is modeled taking both excitonic absorption and subband‐to‐subband absorption into account. It is theoretically shown that the spectral broadening associated with the applied electric fields is largely due to the quantum confinement of the barrier structures. In the InP‐based QW structures absorption spectra, calculated assuming their broadening is due solely to carrier tunneling, successfully explain the measured photocurrent spectra.
TL;DR: In this article, a positron annihilation study of defects created in Si by rf hydrogen plasminar exposure at 275°C was performed, and the Doppler broadening parameter for the annihilation gamma rays was strongly correlated with the hydrogen coverage of the void surfaces.
Abstract: We report a positron annihilation study of defects created in Si by rf hydrogen‐plasma exposure at 275 °C. Analysis of positron annihilation spectroscopy data indicates voidlike structures in a defective ayer extending to ≊14 nm from the surface at a concentration of 1.9±0.5×1020 cm−3. The Doppler broadening parameter for the annihilation gamma rays is strongly correlated to the hydrogen coverage of the void surfaces, voids remain in the Si to at least 800 °C while the hydrogen is desorbed from their surfaces between 600 and 800 °C.
TL;DR: In this article, the frequency spectral broadening of lower hybrid (LH) waves injected into tokamak plasmas is extensively analyzed with reference mostly to experimental data from the ASDEX tokak.
Abstract: The frequency spectral broadening of lower hybrid (LH) waves injected into tokamak plasmas is extensively analysed with reference mostly to experimental data from the ASDEX tokamak. The link between the magnitude of the pump spectral width and the degradation of the LH current drive efficiency (up to a factor of 2), pointed out in previous works, is explained. The experimental behaviour of LH power absorption is also well reproduced, even in situations when the access of the launched LH waves to the core plasma should be largely forbidden. Experiments are described that are aimed at determining whether parametric decay instabilities (PDIs) or scattering of LH waves by density fluctuations in the plasma edge are causes of the broadening of the LH pump frequency spectrum. Fluctuations emerge as the largely dominant process, while no signature of PDI processes is observed. Careful measurements of the density fluctuations in the ASDEX scrape-off layer plasma allow the analytical description given by Andrews and Perkins (1983) to be assumed as the appropriate model for LH scattering. Indeed, it supplies the correct magnitude for the frequency spectral width of the LH pump, and explains quantitatively, together with a ray tracing code, why the CD efficiency decreases with the broadening of the pump spectrum. It can also account for the observed LH power absorption coefficient
TL;DR: In this paper, the authors investigated the possibility of increasing the achievable index of refraction and the slope of the dispersion while simultaneously minimizing absorption in a driven two-level system.
Abstract: We investigate the possibility of increasing the achievable index of refraction and the slope of the dispersion while simultaneously minimizing absorption in a driven two-level system. The analysis is performed non-linearly in both the probing laser field and Doppler and collision broadening have been incorporated for the sake of a realistic treatment. We compare the achievable index of refraction without absorption quantitatively with known results of several favorable three- and four-level systems, find our system less sensitive to Doppler broadening in a collinear set-up of both fields and apply our considerations to the particular example of caesium.
TL;DR: In this paper, the annihilation characteristics of positrons in SiO2 films grown on Si substrates were studied by using monoenergetic positron beams, and it was found that about 90% of the positrons implanted into the SiO 2 film annihilate from positronium (Ps) states.
Abstract: The annihilation characteristics of positrons in SiO2 films grown on Si substrates were studied by using monoenergetic positron beams. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured as a function of incident positron energy for SiO2 (166 nm)/Si specimens fabricated by thermal oxidation. From the measurements, it was found that about 90% of positrons implanted into the SiO2 film annihilate from positronium (Ps) states. This fact was due to the trapping of positrons by open‐space defects and a resultant enhanced formation of Ps in such regions. For the SiO2 film grown at 650 °C, the lifetime of ortho‐Ps was found to be shorter than that in the film grown at 1000 °C. This result suggests that the volume of open‐space defects in the SiO2 film decreased with decreasing the growth rate of the SiO2 film.
TL;DR: Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopic (DBS) measurements were reported on poly(2,2-bis trifluoro 4,5 difluor 1,3-dioxole) over the temperature range 303-423 K as discussed by the authors.
TL;DR: In this paper, a ground-based VLF transmitter was observed onboard the Magion-3 sub-satellite during electron beam injection from the lntercosmos-25 (APEX) satellite.
30 Dec 1994-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a line-shape analysis was applied to non-destructive state analysis of trace amounts of boron in the 10 B(n, α) 7 Li reaction.
Abstract: Prompt γ-ray spectra of recoil 7 Li produced by the 10 B(n, α) 7 Li reaction were measured using neutron beam. The observed Doppler broadening energy spectra were satisfactorily reproduced by a simulation where the velocity degradation of 7 Li within its lifetime of 1.05 × 10 −13 s was estimated using the LSS theory. Our successful line-shape analysis was applied to non-destructive state analysis of trace amounts of boron.
TL;DR: Positron lifetime and Doppler broadening measurements were made on uniformly helium-implanted tungsten to study the evolution of defects and helium bubbles during post-irradiation isochronal annealing as discussed by the authors.
TL;DR: Positron annihilation spectroscopy was carried out on nanocrystalline silver as discussed by the authors, where lifetime and Doppler broadening were measured, and high-resolution electron microscopy observations were also performed.
Abstract: Positron annihilation spectroscopy was carried out on nanocrystalline silver. Both lifetime and Doppler broadening were measured. High-resolution electron microscopy observations were also performed. Diffuse vacancy clusters, the sizes of which correspond to two to four vacancies, and voids of 1–5 nm diameter, were found to reduce the average atomic density of the grain boundary. Some grains grew to a diameter larger than about 70 nm during annealing the specimen from 50 to 100°C. A large fraction of the diffuse vacancy clusters and voids in the boundaries remained after annealing at 400°C. They were stabilized during annealing probably by gaseous atoms.
TL;DR: In this paper, the ν3 fundamental band of the CH3 radical was detected in a refrigerated hollow cathode discharge multipass cell filled with CH4, by using a discharge and laser amplitude double modulation technique, with a difference frequency laser spectrometer and a double phase sensitive detection.
Abstract: In this work several lines of the ν3 fundamental band of the CH3 radical have been detected in a refrigerated hollow cathode discharge multipass cell filled with CH4, by using a discharge and laser amplitude double modulation technique, with a difference frequency laser spectrometer and a double phase sensitive detection. Bands of the precursor CH4 and of C2H4 and C2H6 produced in the discharge have been observed too. By Doppler broadening and absorption variations, the increase of temperature with the establishment of the discharge has been tested. It is only ∼15 °C. Nevertheless, a very high sensitivity in transmittance variations with temperature is achieved for transitions from highly excited levels of stable species. The method proposed can be very useful for the assignment of very weak bands.
TL;DR: In this article, current-driven, electrostatic ion-cyclotron (CDEIC) waves are shown to exhibit amplitude and frequency modulation, spectral broadening, and time-averaged frequency pulling.
Abstract: Modulated, current-driven, electrostatic ion-cyclotron (CDEIC) waves are shown to exhibit amplitude and frequency modulation, spectral broadening, and time-averaged frequency pulling. The observed spectral broadening is asymmetric and sensitively dependent on the driving frequency. Qualitative features of the experimental data are reproduced by the forced van der Pol equation and are explainable using processes associated with driven self oscillations. These results may be relevant to ionospheric modification experiments involving the controlled modulation of the natural electrojet. 31 refs., 4 figs.
TL;DR: In this article, a method for remote measurement of gas temperature, based on spectral collisional shift and broadening, was proposed for the 6 43 -5 50 rotational water line at 439 GHz in the temperature range 250-390 K.
TL;DR: The results of Doppler broadening studies of annealing processes in the commercial stainless steel are presented in this paper, where three models of vacancy sinking and migration were considered.
TL;DR: In this paper, the spectral broadening measurements conducted at S-band (13-cm wavelength) during solar minimum conditions in the heliocentric distance range of 3-8 R(sub O) by Mariner 4, Pioneer 10, Mariner 10, Helios 1,Helios 2, and Viking have been combined to reveal a factor of 2.6 reduction in bandwidth from equator to pole.
Abstract: Spectral broadening measurements conducted at S-band (13-cm wavelength) during solar minimum conditions in the heliocentric distance range of 3-8 R(sub O) by Mariner 4, Pioneer 10, Mariner 10, Helios 1, Helios 2, and Viking have been combined to reveal a factor of 2.6 reduction in bandwidth from equator to pole. Since spectral broadening bandwidth depends on electron density fluctuation and solar wind speed, and latitudinal variation of the former is available from coherence bandwidth measurements, the remote sensing spectral broadening measurements provide the first determination of the latitudinal variation of solar wind speed in the acceleration region. When combined with electron density measurements deduced from white-light coronagraphs, this result also leads to the first determination of the latitudinal variation of mass flux in the acceleration region. From equator to pole, solar wind speed increases by a factor of 2.2, while mass flux decreases by a factor of 2.3. These results are consistent with measurements of solar wind speed by multi-station intensity scintillation measurements, as well as measurements of mass flux inferred from Lyman alpha observations, both of which pertain to the solar wind beyond 0.5 AU. The spectral broadening observations, therefore, strengthen earlier conclusions about the latitudinal variation of solar wind speed and mass flux, and reinforce current solar coronal models and their implications for solar wind acceleration and solar wind modeling.
TL;DR: In this article, a broadband near-infrared pulse covering 700 nm around 2.4 μm has been generated by a dispersion-free parametric mixing in a KTiOPO4 crystal between the fundamental pulse (0.8 μm) from a Ti:sapphire regenerative amplifier and the white continuum pulse.
Abstract: A broadband near‐infrared pulse covering 700 nm around 2.4 μm has been generated by a dispersion‐free parametric mixing in a KTiOPO4 crystal between the fundamental pulse (0.8 μm) from a Ti:sapphire regenerative amplifier and the white continuum pulse. It is tunable within the wavelength region of 1.7–2.9 μm. The comparison with a theoretical bandwidth indicates that the noncollinear phase matching plays a part for the spectral broadening.
TL;DR: In this paper, Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured as a function of isochronal annealing temperature.
Abstract: Defects introduced by 65 MeV proton irradiation into Czochralski-grown Si were investigated by the positron annihilation technique. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured as a function of isochronal annealing temperature. Divacancies introduced by the irradiation were found to migrate above 200° C and they formed stable vacancy-oxygen complexes such as V3On (n=1–3). These defects annealed out at ~500° C. After the recovery of vacancy-oxygen complexes, oxygen clusters were found to be the predominant defect. The aggregation of the oxygen clusters started above 800° C.
TL;DR: In this paper, the scaling of linear growth rate with the electrostatic fluctuation levels is investigated. And the authors show that the scaling is associated with the usual turbulent broadening, while the spectral narrowing is attributed to the presence of coherent structures via self-organization.
Abstract: Experimental results of the scaling of linear growth rate with the electrostatic fluctuation levels are presented. A quadratic scaling was obtained for the ion temperature gradient‐driven instability (ITG), characteristic of weak turbulence. For the rotationally driven E×B mode, a linear scaling was obtained, characteristic of strong turbulence. Moreover, the linear growth rate scaling for the E×B mode exhibited two distinct behaviors, corresponding to a broadening and a narrowing of the spectral width as a function of increasing fluctuation level. The spectral broadening is associated with the usual turbulent broadening, while the spectral narrowing is attributed to the presence of coherent structures via self‐organization. Radial harmonics were detected and shown to contribute to the spread in the spectral width. These structures were also studied via a bispectral analysis. The evolution to the quasicoherent state was also found to result in the presence of a fewer number of radial harmonics in the satu...