Showing papers on "Doppler broadening published in 2012"
TL;DR: In this article, the spin and optical properties of individual nitrogen vacancy centers located within 1-10 nm from the diamond surface were investigated, and stable defects with a characteristic optically detected magnetic-resonance spectrum down to the lowest depth were observed.
Abstract: We investigate spin and optical properties of individual nitrogen vacancy centers located within 1--10 nm from the diamond surface. We observe stable defects with a characteristic optically detected magnetic-resonance spectrum down to the lowest depth. We also find a small but systematic spectral broadening for defects shallower than about 2 nm. This broadening is consistent with the presence of a surface paramagnetic impurity layer [Tisler et al., ACS Nano 3, 1959 (2009)] largely decoupled by motional averaging. The observation of stable and well-behaved defects very close to the surface is critical for single-spin sensors and devices requiring nanometer proximity to the target.
212 citations
TL;DR: In this article, the authors measured the diffuse reflection spectrum of solid samples such as explosives (TNT, RDX, PETN), fertilizers (ammonium nitrate, urea), and paints (automotive and military grade) at a stand-off distance of 5m using a mid-infrared supercontinuum light source with 3.9 W average output power.
Abstract: We measure the diffuse reflection spectrum of solid samples such as explosives (TNT, RDX, PETN), fertilizers (ammonium nitrate, urea), and paints (automotive and military grade) at a stand-off distance of 5 m using a mid-infrared supercontinuum light source with 3.9 W average output power. The output spectrum extends from 750–4300 nm, and it is generated by nonlinear spectral broadening in a 9 m long fluoride fiber pumped by high peak power pulses from a dual-stage erbium-ytterbium fiber amplifier operating at 1543 nm. The samples are distinguished using unique spectral signatures that are attributed to the molecular vibrations of the constituents. Signal-to-noise ratio (SNR) calculations demonstrate the feasibility of increasing the stand-off distance from 5 to ∼150 m, with a corresponding drop in SNR from 28 to 10 dB.
124 citations
TL;DR: In this paper, the spectral analysis and error propagation techniques associated with x-ray imaging crystal spectroscopy (XICS) have been used to accurately constrain particle, momentum, and heat transport studies in a tokamak for the first time.
Abstract: This research describes advancements in the spectral analysis and error propagation techniques associated with x-ray imaging crystal spectroscopy (XICS) that have enabled this diagnostic to be used to accurately constrain particle, momentum, and heat transport studies in a tokamak for the first time. Doppler tomography techniques have been extended to include propagation of statistical uncertainty due to photon noise, the effect of non-uniform instrumental broadening as well as flux surface variations in impurity density. These methods have been deployed as a suite of modeling and analysis tools, written in interactive data language (IDL) and designed for general use on tokamaks. Its application to the Alcator C-Mod XICS is discussed, along with novel spectral and spatial calibration techniques. Example ion temperature and radial electric field profiles from recent I-mode plasmas are shown, and the impact of poloidally asymmetric impurity density and natural line broadening is discussed in the context of the planned ITER x-ray crystal spectrometer.
71 citations
TL;DR: A detailed investigation of the excited states accessed by UV absorption in alternating DNA duplexes was performed, indicating that most excited states are delocalized over at most two bases, and charge transfer states are located at higher energies than the bright states in the Franck-Condon region.
Abstract: A detailed investigation of the excited states accessed by UV absorption in alternating DNA duplexes was performed by means of an extensive sampling of intra- and intermolecular degrees of freedom. The excited states were computed using the algebraic diagrammatic construction method to second-order (ADC(2)). A realistic DNA environment was included through an electrostatic embedding QM/MM coupling scheme. The results indicate that (i) most excited states are delocalized over at most two bases, (ii) charge transfer states are located at higher energies than the bright states in the Franck–Condon region, but (iii) coupling between locally excited and charge transfer states may provide a route to dynamical charge separation, and (iv) spectral broadening is mainly caused by intramolecular vibrations.
66 citations
TL;DR: In this article, a methodology to allow on-the-fly Doppler broadening of neutron cross sections for use in Monte Carlo codes has been developed based on a combination of Taylor series expansions and asymptotic series expansions.
Abstract: A methodology to allow on-the-fly Doppler broadening of neutron cross sections for use in Monte Carlo codes has been developed. The Monte Carlo code only needs to store 0K cross sections for each isotope and the method will broaden the 0K cross sections for any isotope in the library to any temperature in the range 77K-3200K. The methodology is based on a combination of Taylor series expansions and asymptotic series expansions. The type of series representation was determined by investigating the temperature dependence of U238 resonance cross sections in three regions: near the resonance peaks, mid-resonance, and the resonance wings. The coefficients for these series expansions were determined by a regression over the energy and temperature range of interest. Since the resonance parameters are a function of the neutron energy and target nuclide, the ψ and χ functions in the Adler-Adler multi-level resonance model can be represented by series expansions in temperature only, allowing the least number of terms to approximate the temperature dependent cross sections within a given accuracy. The comparison of the broadened cross sections using this methodology with the NJOY cross sections was excellent over the entire temperature range (77K-3200K) and energy range. A Monte Carlo code was implemented to apply the combined regression model and used to estimate the additional computing cost which was found to be less than <1%.
53 citations
TL;DR: In this paper, a colloidal solution of PbS quantum dots was used to study the nonlinear optical response of nearly degenerate quantum confined nanostructures with femtosecond temporal resolution despite extensive line broadening caused by the finite size distribution found in colloidal solutions.
Abstract: Quantum dots exhibit rich and complex electronic structure that makes them ideal for studying the basic physics of semiconductors in the intermediate regime between bulk materials and single atoms. The remarkable nonlinear optical properties of these nanostructures make them strong candidates for photonics applications. Here, we experimentally probe changes in the fine structure on ultrafast timescales of a colloidal solution of PbS quantum dots through their nonlinear optical response despite extensive inhomogeneous spectral broadening. Using continuum excitation and detection, we observe electronic coupling between nearly degenerate exciton states split by intervalley scattering at low exciton occupancy and a sub-100 fs frequency shift presumably due to phonon-assisted transitions. At high excitation intensities, we observe multi-exciton effects and sharp absorbance bands indicative of exciton-exciton coupling. Our experiments directly probe the nonlinear optical response of nearly degenerate quantum confined nanostructures with femtosecond temporal resolution despite extensive line broadening caused by the finite size distribution found in colloidal solutions.
51 citations
TL;DR: In this article, high-resolution?-ray measurements were carried out on the Joint European Torus (JET) in an experiment aimed at accelerating 4He ions in the MeV range by coupling third harmonic radio frequency heating to an injected 4He beam.
Abstract: High-resolution ?-ray measurements were carried out on the Joint European Torus (JET) in an experiment aimed at accelerating 4He ions in the MeV range by coupling third harmonic radio frequency heating to an injected 4He beam. For the first time, Doppler broadening of ?-ray peaks from the 12C(d, p?)13C and 9Be(?, n?)12C reactions was observed and interpreted with dedicated Monte Carlo codes based on the detailed nuclear physics of the processes. Information on the confined 4He and deuteron energy distribution was inferred, and confined 4He ions with energies as high as 6?MeV were assessed. A signature of MHD activity in ?-ray traces was also detected. The reported results have a bearing on diagnostics for fast ions in the MeV range in next step fusion devices.
49 citations
TL;DR: The model proposed in this article is the first model that has successfully predicted speckle broadening in a self-mixing velocimetry sensor in a quantitative manner and was found that the beam spot size on the target and the target speed affect the resulting spectral broadening caused by Speckle.
Abstract: Self-mixing laser sensors require few components and can be used to measure velocity The self-mixing laser sensor consists of a laser emitting a beam focused onto a rough target that scatters the beam with some of the emission re-entering the laser cavity This ‘self-mixing’ causes measurable interferometric modulation of the laser output power that leads to a periodic Doppler signal spectrum with a peak at a frequency proportional to the velocity of the target Scattering of the laser emission from a rough surface also leads to a speckle effect that modulates the Doppler signal causing broadening of the signal spectrum adding uncertainty to the velocity measurement This article analyzes the speckle effect to provide an analytic equation to predict the spectral broadening of an acquired self-mixing signal and compares the predicted broadening to experimental results To the best of our knowledge, the model proposed in this article is the first model that has successfully predicted speckle broadening in a self-mixing velocimetry sensor in a quantitative manner It was found that the beam spot size on the target and the target speed affect the resulting spectral broadening caused by speckle It was also found that the broadening is only weakly dependent on target angle The experimental broadening was consistently greater than the theoretical speckle broadening due to other effects that also contribute to the total broadening
44 citations
TL;DR: The successful fabrication of mid-infrared waveguides written in a gallium lanthanum sulphide (GLS) substrate via the ultrafast laser inscription technique is reported.
Abstract: We report the successful fabrication of mid-infrared waveguides written in a gallium lanthanum sulphide (GLS) substrate via the ultrafast laser inscription technique. Single mode guiding at 2485 nm and 3850 nm is observed. Spectral broadening spanning 1500 nm (-15dB points) is demonstrated under 3850 nm excitation.
39 citations
TL;DR: In this article, the mass splitting between D+ and D^- mesons is moderate, not in excess of 100 MeV when the decay channel into quasifree quarks opens (Mott effect) at densities above twice saturation density.
Abstract: We study D meson resonances in hot, dense quark matter within the NJL model and its Polyakov-loop extension We show that the mass splitting between D^+ and D^- mesons is moderate, not in excess of 100 MeV When the decay channel into quasifree quarks opens (Mott effect) at densities above twice saturation density, the decay width reaches rapidly the value of 200 MeV which entails a spectral broadening sufficient to open J/psi dissociation processes Contrary to results from hadronic mean-field theories, the chiral quark model does not support the scenario of a dropping D meson masses so that scenarios for J/psi dissociation by quark rearrangement built on the lowering of the threshold for this process in a hot and dense medium have to be reconsidered and should account for the spectral broadening
31 citations
TL;DR: The novel theory of nonradiative decay of the intramolecular charge-transfer excited states is carried out for dyes and organic compounds of different nature, both for polar and nonpolar media.
Abstract: The fluctuations of orientation and induction interactions in solution and their impact on the broadening of absorption and fluorescence spectra are considered in terms of a bands-of-energy model. Also covered is the application of principles of thermodynamics and self-organization of systems for calculation of solvatochromic shift, among them a component owing to the work on electronic polarization of solvent at the instant of electronic transition in the solute. The findings on solvatochromic shift and spectral broadening open the way to the calculation of solvent effects on the rate constant of nonradiative transitions. As demonstrated herein for 15 fluorophores, the novel theory of nonradiative decay of the intramolecular charge-transfer excited states is carried out for dyes and organic compounds of different nature, both for polar and nonpolar media.
TL;DR: In this paper, the shape of the output spectrum of incoherent light pulses in a relatively short active fiber is treated, and the spectrum is shown to be composed of two different-scale structures: a narrow central part copying the initial shape and broad exponential tails that grow with increasing output power.
Abstract: Amplification of incoherent light pulses in a relatively short active fiber is treated Spectral broadening due to the self-phase modulation effect at negligibly small dispersion has been studied theoretically The expression for the shape of the output spectrum has been obtained for input pulses of arbitrary temporal and spectral shape at various gain coefficients The expression is found to be simplified in case of a hyperbolic secant temporal shape The calculated shapes have been compared with the experimentally measured spectra for Q-switched fiber laser nanosecond pulses amplified in Yb-doped fiber, demonstrating excellent agreement of theory and experiment The spectrum of the output pulse is shown to be composed of two different-scale structures: a narrow central part copying the initial shape and broad exponential tails that grow with increasing output power
TL;DR: In this paper, the microstructures, irradiation-induced defects and changes of mechanical property of Chinese domestic A508-3 steels after proton irradiation were investigated by TEM, positron lifetime, slow positron beam Doppler broadening spectroscopy and hardness measurements.
TL;DR: In this paper, the authors analyzed pulse broadening caused by atmospheric dispersion, which is the key factor in high-speed and long-distance free space laser communication systems according to their simulation.
TL;DR: In this paper, a theoretical model using the density matrix approach has been presented to show the influence of multiple excited states on electromagnetically induced transparency (EIT) in a cascade-type Doppler broadened medium.
Abstract: A theoretical model using the density matrix approach has been presented to show the influence of multiple excited states on electromagnetically induced transparency (EIT) in a cascade-type Doppler broadened medium. A five-level system has been considered that is a simple case of the 87Rb atom. In a room temperature vapour, when the Doppler broadening is comparable with hyperfine splitting in the middle states, there is a strong reduction in EIT. By performing the thermal averaging in the five-level Doppler broadened system, we observe an asymmetric transparency that has already been shown in most of the experimental work.
TL;DR: In this article, a self-consistent calculation of the rotational polarization density using linearized density matrix theory was proposed to simulate femtosecond pulse sequences in which they have been delayed by exactly the rotation period.
Abstract: A sequence of femtosecond laser pulses propagating through atmosphere and delayed near the rotational recurrence period of N${}_{2}$ can resonantly drive molecular alignment. Through the polarization density, the molecular alignment provides an index of refraction contribution that acts as a lens copropagating with each laser pulse. Each pulse enhances this contribution to the index, modifying the propagation of subsequent pulses. Here we present propagation simulations of femtosecond pulse sequences in which we have implemented a self-consistent calculation of the rotational polarization density using linearized density matrix theory. We find that a femtosecond pulse sequence can enhance pulse compression or collimation in atmosphere. In particular, when the pulses are delayed by exactly the rotational recurrence period, each subsequent pulse is increasingly compressed due to a combination of spectral broadening and negative dispersion. Alternatively, when the intensity peak of each pulse is centered on the maximum index generated by the preceding pulses, each pulse is increasingly collimated.
TL;DR: In this paper, a small sample of nearby near-infrared bright massive and intermediate-mass young stellar objects using emission lines sensitive to discs and winds was used to study the kinematical properties of these stars.
Abstract: We present a study of the kinematical properties of a small sample of nearby near-infrared bright massive and intermediate-mass young stellar objects using emission lines sensitive to discs and winds. We show for the first time that the broad (∼500 km s−1) symmetric line wings on the H i Brackett series lines are due to Stark broadening or electron scattering, rather than pure Doppler broadening due to high-speed motion. The results are consistent with the presence of a very dense circumstellar environment. In addition, many of these lines show evidence for weak line self-absorption, suggestive of a wind or disc–wind origin for that part of the absorbing material. The weakness of the self-absorption suggests a large opening angle for such an outflow. We also study the fluorescent 1.688 μm Fe ii line, which is sensitive to dense material. We fitted a Keplerian disc model to this line, and find reasonable fits in all bar one case, in agreement with previous finding for classical Be stars that fluorescent iron transitions are reasonable disc tracers. Overall, the evidence suggests these stars still have accretion discs, with a very dense ionized inner circumstellar environment which may be tracing either the inner regions of the disc or of a stellar wind, and in which ionized outflow is also present. The similarity with lower mass stars is striking, suggesting that at least in this mass range they form in a similar fashion.
TL;DR: A concise overview of the probe techniques of positron annihilation and their use for studying the electronic structure and open volume defects in a wide range of materials can be found in this paper.
Abstract: This chapter gives a concise overview of the probe techniques of positron annihilation and their use for studying the electronic structure and open volume defects in a wide range of materials. The first part introduces the behavior of positrons in solids, in particular the trapping and annihilation of positrons at defect sites. In this context, the focus is on the interrelations between the annihilation characteristics observed and the type, concentration, and electronic structure of defects.
The three basic techniques of positron lifetime spectroscopy as well as Doppler broadening and angular correlation of the positron-electron annihilation radiation are discussed in detail together with practical aspects such as positron sources, sample preparation, and instrumentation. Special attention is given to novel developments such as coincident Doppler broadening measurements with chemical sensitivity, and advances in positron beam techniques. Studies of near-surface defects and depth profiling with monoenergetic beams of low-energy positrons are described.
The versatility of positron annihilation techniques is demonstrated by selected examples of vacancy studies in ordered intermetallic alloys and semiconductors and free volumes in highly disordered materials.
Keywords:
vacancies;
crystal defects;
open-volume defects;
electron momentum;
doppler broadening;
positron lifetime spectroscopy;
angular correlation of annihilation radiation (ACAR);
positron beam techniques
TL;DR: In this article, the authors examined the local spectral shift, energy depletion, and action conservation of nonlinear laser pulses using the modified paraxial simulation code WAKE, which is based on the assumption of slow temporal variation of the pulse envelope.
Abstract: Laser pulses propagating through plasma undergo spectral broadening through local energy exchange with driven plasma waves. For propagation distances on the order of the energy depletion length, spectral shifts can be comparable to the laser central frequency and wavenumber, a result of approximate action conservation. Here, we examine the local spectral shift, energy depletion, and action conservation of nonlinear laser pulses using the modified paraxial simulation code WAKE. Breakdown of the modified paraxial equation (MPE), which is based on the assumption of slow temporal variation of the pulse envelope, is monitored via consideration of the wave action. Although action is theoretically conserved for the continuous MPE, we observe that for large red shifts, action decays for the discrete implementation. Numerical analysis of the propagation algorithm verified the observed behavior. Increasing resolution improves action conservation up to a time, which is identified to be the validity limit for the MPE. Increased resolution also leads to increased simulation times and eliminates the strength of the MPE solver–efficiency.
TL;DR: Theoretical pressure broadening and line shifts are compared with experimental values for three water rotational transitions as mentioned in this paper, which are primary radiant coolants for collapsing interstellar clouds that contain water.
Abstract: Theoretical ${\mathrm{H}}_{2}\mathrm{O}--{\mathrm{H}}_{2}$ pressure broadening and line shifts are compared with experimental values for three water rotational transitions. These transitions, which occur at terahertz frequencies, are primary radiant coolants for collapsing interstellar clouds that contain water. They are observed by the submillimeter/FIR Herschel space observatory. Systematic effects in previous pressure-broadening measurements that were due to ortho-hydrogen to para-hydrogen conversion have been overcome, and the present results follow the expected behavior predicted by collision theory. The systemic error, discovered through comparisons between theory and experiments, is due to conversion of ortho hydrogen to para hydrogen by water ice below 40 K. This process occurs on a time scale very short compared to astrophysical processes and may be pertinent to ice-grain interactions in the interstellar medium.
TL;DR: In this article, a detailed study on a set of Si:H samples with a wide variety of nanostructural properties, including dense up to porous films and amorphous up to highly crystalline films, using Doppler broadening positron annihilation spectroscopy (DB-PAS) and Fourier Transform infrared (FTIR) was presented.
Abstract: Due to the complex nature of hydrogenated amorphous and microcrystalline silicon (a-Si:H; μc-Si:H) a profound understanding of the Si:H nanostructure and its relation to the Staebler–Wronski effect (SWE) is still lacking. In order to gain more insight into the nanostructure we present a detailed study on a set of Si:H samples with a wide variety of nanostructural properties, including dense up to porous films and amorphous up to highly crystalline films, using Doppler broadening positron annihilation spectroscopy (DB-PAS) and Fourier Transform infrared (FTIR) spectroscopy. The results obtained from these material characterisation techniques show that they are powerful complementary methods in the analysis of the Si:H nanostructure. Both techniques indicate that the dominant type of open volume deficiency in device grade a-Si:H seems to be the divacancy, which is in line with earlier positron annihilation lifetime spectroscopy (PALS), Doppler broadening (DB) PAS and FTIR studies.
TL;DR: In this paper, the chemical environment inside free volume holes in a series of halogenated polystyrenes (p-position), −[CH2CH C6H5X]n- (X = F, Cl, Br, I), was provided by using positron annihilation spectroscopy.
Abstract: In this paper, a systematic study is provided of the chemical environment inside free volume holes in a series of halogenated polystyrenes (p-position), −[CH2CH C6H5X]n– (X = F, Cl, Br, I), by using positron annihilation spectroscopy. In such polymers it was determined that the chemical environment is the major effect on Doppler broadening of two 511 keV γ photons from positron–electron annihilation. Doppler broadening energy spectroscopy (DBES) and positron annihilation lifetime spectroscopy (PALS) were combined in a novel approach to study the chemical environment in a polymer system. A highly linear relationship between Doppler broadenings caused by electron kinetic energies of valence electrons and the ionization potentials of halogen elements was obtained, as well as a similar correlation with the results from ab initio molecular orbital (MO) calculations for monohalogenobenzenes, C6H5X (X = F, Cl, Br, I). The results demonstrate that the combination of DBES and PALS may provide an effective way to s...
TL;DR: In this article, the defect species detected by positron annihilation were identified as cation vacancies coupled with multiple nitrogen vacancies (VNs), and their introduction mechanism was discussed in terms of the strain energy due to bond-length/angle distortions and the suppression of the VN formation energy by neighboring In atoms.
Abstract: Native defects in InxGa1–xN grown by plasma-assisted molecular beam epitaxy were probed by a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured, and these were compared with results obtained using first-principles calculation. The defect concentration increased with increasing In composition x and reached the maximum at x = 0.44∼0.56. A clear correlation between the line-width of photoluminescence and the defect concentration was obtained. The major defect species detected by positron annihilation was identified as cation vacancies coupled with multiple nitrogen vacancies (VNs), and their introduction mechanism is discussed in terms of the strain energy due to bond-length/angle distortions and the suppression of the VN formation energy by neighboring In atoms.
TL;DR: A synthetic DBS diagnostic is described, which has been used for comparisons between measurements in the DIII-D tokamak and predictions from nonlinear gyrokinetic simulations.
Abstract: Doppler backscattering (DBS) is a plasma diagnostic used in tokamaks and other magnetic confinement devices to measure the fluctuation level of intermediate wavenumber (kθρs ∼ 1) density fluctuations and the lab frame propagation velocity of turbulence. Here, a synthetic DBS diagnostic is described, which has been used for comparisons between measurements in the DIII-D tokamak and predictions from nonlinear gyrokinetic simulations. To estimate the wavenumber range to which a Gaussian beam would be sensitive, a ray tracing code and a 2D finite difference, time domain full wave code are used. Experimental density profiles and magnetic geometry are used along with the experimental antenna and beam characteristics. An example of the effect of the synthetic diagnostic on the output of a nonlinear gyrokinetic simulation is presented.
TL;DR: In this paper, the authors measured the Doppler broadening of annihilation radiation (DBAR) spectra of $3d$ (Fe, Co, and Ni) and $4f$ (Gd, Tb, and Dy) ferromagnets under a magnetic field by using spin-polarized positrons from a Ga source.
Abstract: We measured the Doppler broadening of annihilation radiation (DBAR) spectra of $3d$ (Fe, Co, and Ni) and $4f$ (Gd, Tb, and Dy) ferromagnets under a magnetic field by using spin-polarized positrons from a ${}^{68}$Ge-${}^{68}$Ga source. The results showed that the DBAR spectra of these metals have notably different magnetic-field dependences. The differences among Fe, Co, and Ni reflect that the upper minority spin bands of Fe and Co are nearly empty while those of Ni are still mostly occupied. For the rare-earth metals instead of the inner $4f$ electrons, $5d$ electrons that mediate the exchange interaction of the $4f$ electrons are primarily responsible for the magnetic-field effects on the DBAR spectra. Furthermore, the magnetic-field effects on the DBAR spectra of Gd, Tb, and Dy vanished above the Curie temperatures of the magnetic-phase transition for these metals.
TL;DR: In this paper, the authors demonstrate that stimulated supercontinuum generation alleviates restrictions on spectral broadening in silicon waveguides at telecommunications wavelengths, where two-photon and free-carrier absorption typically deplete the pump before large broadening factors can be achieved.
Abstract: We demonstrate that stimulated supercontinuum generation alleviates restrictions on spectral broadening in silicon waveguides At telecommunications wavelengths, two-photon and free-carrier absorption typically deplete the pump before large broadening factors can be achieved However, broadening via modulation instability (MI) can be enhanced by seeding, which also substantially improves the energy efficiency of spectral broadening in media with nonlinear loss Coherent seeding also generates a stable output spectrum, in contrast to conventional approaches where broadening starts from noise The combination of self-phase modulation and stimulated modulation instability generates broadening factors in excess of 40-fold at moderate intensity levels, with >15-times better energy efficiency
15 Aug 2012-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the positron beam Doppler broadening was used to detect vacancy-type defects in solids, especially defects induced by ion irradiation/implantation that are localized near the surface.
Abstract: The positron beam technique has been widely used as a detection tool for vacancy-type defects in solids, especially defects induced by ion irradiation/implantation that are localized near the surface. To extend this technique to other applications, we constructed unique in situ positron beam measurement equipment combined with an ion beam irradiation chamber. This equipment enables us to measure positron beam Doppler broadening during or immediately after irradiation without any sample handling. With this equipment, defect accumulation and evolution in iron and nickel were investigated at room temperature. In addition, the defect accumulation and annealing process was investigated at temperature below stage III to reveal vacancy configurations after cascade, without any thermal migration after the cascade cooling. In this paper, we summarize these results and discuss ideas for future study.
TL;DR: In this paper, the authors calculate power-dependent corrections to the Voigt profile, which are parametrized by the Gaussian Doppler width, the Lorentzian natural linewidth, and the optical depth.
Abstract: The Voigt profile—a convolution of a Gaussian and a Lorentzian—accurately describes the absorption lines of atomic and molecular gases at low probe powers. Fitting experimental absorption data to such a Voigt profile yields both the Lorentzian natural linewidth and the Gaussian Doppler broadening. However, as the probe power increases, saturation effects change the absorption line shape, such that it is no longer accurately described by a Voigt profile. Naively fitting a simple Voigt profile to the absorption line therefore introduces spurious power dependence into the extracted Doppler component. Using a simple atomic model, we calculate power-dependent corrections to the Voigt profile, which are parametrized by the Gaussian Doppler width, the Lorentzian natural linewidth, and the optical depth. We show numerically and experimentally that including the correction term substantially reduces the spurious power dependence in the fitted Gaussian width.
Journal Article•
TL;DR: In this article, a self-consistent calculation of the rotational polarization density using linearized density matrix theory is proposed to enhance femtosecond pulse compression or collimation in atmosphere.
Abstract: A sequence of femtosecond laser pulses propagating through atmosphere and delayed near the rotational recurrence period of N2 can resonantly drivemolecular alignment. Through the polarization density, themolecular alignment provides an index of refraction contribution that acts as a lens copropagating with each laser pulse. Each pulse enhances this contribution to the index, modifying the propagation of subsequent pulses. Here we present propagation simulations of femtosecond pulse sequences in which we have implemented a self-consistent calculation of the rotational polarization density using linearized densitymatrix theory.Wefind that a femtosecond pulse sequence can enhance pulse compression or collimation in atmosphere. In particular, when the pulses are delayed by exactly the rotational recurrence period, each subsequent pulse is increasingly compressed due to a combination of spectral broadening and negative dispersion. Alternatively, when the intensity peak of each pulse is centered on the maximum index generated by the preceding pulses, each pulse is increasingly collimated.
TL;DR: In this paper, a measurement scheme for determining an absorption profile with an accuracy imposed solely by photon shot noise is presented, where the spectral profile at a frequency detuning more than 200 natural linewidths from the line center is used to discover an optically induced broadening process.
Abstract: Here, we report a measurement scheme for determining an absorption profile with an accuracy imposed solely by photon shot noise. We demonstrate the power of this technique by measuring the absorption of cesium vapor with an uncertainty at the 2-ppm level. This extremely high signal-to-noise ratio allows us to directly observe the homogeneous line-shape component of the spectral profile, even in the presence of Doppler broadening, by measuring the spectral profile at a frequency detuning more than 200 natural linewidths from the line center. We then use this tool to discover an optically induced broadening process that is quite distinct from the well-known power broadening phenomenon.