Showing papers on "Ionization published in 2015"
TL;DR: A multidimensional approach, based on the measurement and accurate theoretical description of both even and odd harmonic orders, enabled us to reconstruct both quantum amplitudes and phases of the electronic states with a resolution of ~100 attoseconds.
Abstract: The ultrafast motion of electrons and holes after light-matter interaction is fundamental to a broad range of chemical and biophysical processes. We advanced high-harmonic spectroscopy to resolve spatially and temporally the migration of an electron hole immediately after ionization of iodoacetylene while simultaneously demonstrating extensive control over the process. A multidimensional approach, based on the measurement and accurate theoretical description of both even and odd harmonic orders, enabled us to reconstruct both quantum amplitudes and phases of the electronic states with a resolution of ~100 attoseconds. We separately reconstructed quasi-field-free and laser-controlled charge migration as a function of the spatial orientation of the molecule and determined the shape of the hole created by ionization. Our technique opens the prospect of laser control over electronic primary processes.
448 citations
TL;DR: In this article, the authors present observations targeting transitions of the oxygen-bearing ions OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources.
Abstract: In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2 Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (ζH) and molecular hydrogen fraction (f_H_2) We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines From the molecular abundances we compute f_H_2 in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0042 ± 0018 This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions We also infer ζH throughout our sample, and find a lognormal distribution with mean log (ζH) = –1575 (ζH = 178 × 10–16 s–1) and standard deviation 029 for gas within the Galactic disk, but outside of the Galactic center This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H_3^+ observations Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies
235 citations
TL;DR: In this paper, an observational and theoretical study of the primary ionizing agents (cosmic rays (CRs) and X-rays) in the TW Hya protoplanetary disk is presented.
Abstract: We present an observational and theoretical study of the primary ionizing agents (cosmic rays (CRs) and X-rays) in the TW Hya protoplanetary disk. We use a set of resolved and unresolved observations of molecular ions and other molecular species, encompassing 11 lines total, in concert with a grid of disk chemistry models. The molecular ion constraints comprise new data from the Submillimeter Array on HCO+, acquired at unprecedented spatial resolution, and data from the literature, including ALMA observations of N2H+. We vary the model incident CR flux and stellar X-ray spectra and find that TW Hya's HCO+ and N2H+ emission are best-fit by a moderately hard X-ray spectra, as would be expected during the flaring state of the star, and a low CR ionization rate, ?CR 10?19 s?1. This low CR rate is the first indication of the presence of CR exclusion by winds and/or magnetic fields in an actively accreting T Tauri disk system. With this new constraint, our best-fit ionization structure predicts a low turbulence dead-zone extending from the inner edge of the disk out to 50-65 AU. This region coincides with an observed concentration of millimeter grains, and we propose that the inner region of TW Hya is a dust (and possibly planet) growth factory as predicted by previous theoretical work.
219 citations
TL;DR: In this article, the applicability of the theory, its relation to the Landau-Dykhne method, and its application to the ionization of atoms by ultrashort nonmonochromatic laser pulses of an arbitrary shape are discussed.
Abstract: We review the status of the theory of ionization of atoms and ions by intense laser radiation (Keldysh's theory). We discuss the applicability of the theory, its relation to the Landau–Dykhne method, and its application to the ionization of atoms by ultrashort nonmonochromatic laser pulses of an arbitrary shape. The semiclassical imaginary time method is applied to describe electron sub-barrier motion using classical equations of motion with an imaginary time i for an electron in the field of an electromagnetic wave. We also discuss tunneling interference of transition amplitudes, a phenomenon occurring due to the existence of several saddle points in the complex time plane and leading to fast oscillations in the momentum distribution of photoelectrons. Nonperturbatively taking the Coulomb interaction between an outgoing electron and the atomic residual into account causes significant changes in the photoelectron momentum distribution and in the level ionization rates, the latter usually increasing by orders of magnitude for both tunneling and multiquantum ionization. The effect of a static magnetic field on the ionization rate and the magnetic cumulation process is examined. The theory of relativistic tunneling is discussed, relativistic and spin corrections to the ionization rate are calculated, and the applicability limits of the nonrelativistic Keldysh theory are determined. Finally, the application of the Fock method to the covariant description of nonlinear ionization in the relativistic regime is discussed.
193 citations
TL;DR: This work reports on an alternative principle for detecting the magnetic resonance of nitrogen-vacancy centres, allowing the direct photoelectric readout ofnitrogen-v Vacancy centres spin state in an all-diamond device.
Abstract: The readout of negatively charged nitrogen-vacancy centre electron spins is essential for applications in quantum computation, metrology and sensing. Conventional readout protocols are based on the detection of photons emitted from nitrogen-vacancy centres, a process limited by the efficiency of photon collection. We report on an alternative principle for detecting the magnetic resonance of nitrogen-vacancy centres, allowing the direct photoelectric readout of nitrogen-vacancy centres spin state in an all-diamond device. The photocurrent detection of magnetic resonance scheme is based on the detection of charge carriers promoted to the conduction band of diamond by two-photon ionization of nitrogen-vacancy centres. The optical and photoelectric detection of magnetic resonance are compared, by performing both types of measurements simultaneously. The minima detected in the measured photocurrent at resonant microwave frequencies are attributed to the spin-dependent ionization dynamics of nitrogen-vacancy, originating from spin-selective non-radiative transitions to the metastable singlet state.
185 citations
TL;DR: In this article, the rate coefficients for ionization and dissociation in the radiation fields of the quiet and the active Sun at 1 AU heliocentric distance and blackbodies at four selected temperatures in the range from T = 1000 K to 1,000,000 K without factors for radiation dilution with distance from the source were calculated.
173 citations
TL;DR: In this article, the ionization and kinematics of the ionized gas in the nuclear region of the barred Seyfert 2 galaxy NGC 5643 were studied using MUSE integral field observations in the framework of the Measuring Active Galactic Nuclei Under MUSE Microscope (MAGNUM) survey.
Abstract: We study the ionization and kinematics of the ionized gas in the nuclear region of the barred Seyfert 2 galaxy NGC 5643 using MUSE integral field observations in the framework of the Measuring Active Galactic Nuclei Under MUSE Microscope (MAGNUM) survey. The data were used to identify regions with different ionization conditions and to map the gas density and the dust extinction. We find evidence for a double-sided ionization cone, possibly collimated by a dusty structure surrounding the nucleus. At the center of the ionization cone, outflowing ionized gas is revealed as a blueshifted, asymmetric wing of the [OIII] emission line, up to projected velocity v 10 ~ −450 km s-1 . The outflow is also seen as a diffuse, low-luminosity radio and X-ray jet, with similar extension. The outflowing material points in the direction of two clumps characterized by prominent line emission with spectra typical of HII regions, located at the edge of the dust lane of the bar. We propose that the star formation in the clumps is due to positive feedback induced by gas compression by the nuclear outflow, providing the first candidate for outflow-induced star formation in a Seyfert-like, radio-quiet AGN. This suggests that positive feedback may be a relevant mechanism in shaping the black hole-host galaxy coevolution.
157 citations
TL;DR: In this paper, the authors analyzed atmospheric pressure plasma propagation inside long dielectric tubes through nonintrusive and nonperturbative time resolved bi-directional electric field (EF) measurements.
Abstract: Atmospheric pressure plasma propagation inside long dielectric tubes is analyzed for the first time through nonintrusive and nonperturbative time resolved bi-directional electric field (EF) measurements. This study unveils that plasma propagation occurs in a region where longitudinal EF exists ahead the ionization front position usually revealed from plasma emission with ICCD measurement. The ionization front propagation induces the sudden rise of a radial EF component. Both of these EF components have an amplitude of several kV/cm for helium or neon plasmas and are preserved almost constant along a few tens of cm inside a capillary. All these experimental measurements are in excellent agreement with previous model calculations. The key roles of the voltage pulse polarity and of the target nature on the helium flow patterns when plasma jet is emerging in ambient air are documented from Schlieren visualization. The second part of this work is then dedicated to the development of multi jet systems, using two different setups, based on a single plasma source. Plasma splitting in dielectric tubes drilled with sub millimetric orifices, but also plasma transfer across metallic tubes equipped with such orifices are reported and analyzed from ICCD imaging and time resolved EF measurements. This allows for the design and the feasibility validation of plasma jet arrays but also emphasizes the necessity to account for voltage pulse polarity, target potential status, consecutive helium flow modulation, and electrostatic influence between the produced secondary jets.
156 citations
TL;DR: In this article, it was shown that the CO2 conversion in a dielectric barrier discharge rises drastically upon addition of Ar or He, and the effect is more pronounced for Ar than for He.
Abstract: This paper demonstrates that the CO2 conversion in a dielectric barrier discharge rises drastically upon addition of Ar or He, and the effect is more pronounced for Ar than for He. The effective CO2 conversion, on the other hand, drops upon addition of Ar or He, which is logical due to the lower CO2 content in the gas mixture, and the same is true for the energy efficiency, because a considerable fraction of the energy is then consumed into ionization/excitation of Ar or He atoms. The higher absolute CO2 conversion upon addition of Ar or He can be explained by studying in detail the Lissajous plots and the current profiles. The breakdown voltage is lower in the CO2/Ar and CO2/He mixtures, and the discharge gap is more filled with plasma, which enhances the possibility for CO2 conversion. The rates of electron impact excitation–dissociation of CO2, estimated from the electron densities and mean electron energies, are indeed higher in the CO2/Ar and (to a lower extent) in the CO2/He mixtures, compared to the pure CO2 plasma. Moreover, charge transfer between Ar+ or Ar2+ ions and CO2, followed by electron-ion dissociative recombination of the CO2+ ions, might also contribute to, or even be dominant for the CO2 dissociation. All these effects can explain the higher CO2 conversion, especially upon addition of Ar, but also upon addition of He.
147 citations
TL;DR: It is shown directly that NEMS-MS analysis is insensitive to charge state: the spectrum consists of a single peak whatever the species’ charge state, making it significantly clearer than existing MS analysis.
Abstract: Current approaches to mass spectrometry (MS) require ionization of the analytes of interest. For high-mass species, the resulting charge state distribution can be complex and difficult to interpret correctly. Here, using a setup comprising both conventional time-of-flight MS (TOF-MS) and nano-electromechanical systems-based MS (NEMS-MS) in situ, we show directly that NEMS-MS analysis is insensitive to charge state: the spectrum consists of a single peak whatever the species’ charge state, making it significantly clearer than existing MS analysis. In subsequent tests, all the charged particles are electrostatically removed from the beam, and unlike TOF-MS, NEMS-MS can still measure masses. This demonstrates the possibility to measure mass spectra for neutral particles. Thus, it is possible to envisage MS-based studies of analytes that are incompatible with current ionization techniques and the way is now open for the development of cutting-edge system architectures with unique analytical capability.
140 citations
TL;DR: In this paper, the authors measured the scintillation and ionization yield of recoiling nuclei in liquid argon as a function of applied electric field by exposing a dual-phase LAr-TPC to a low energy pulsed narrow band neutron beam produced at the Notre Dame Institute for Structure and Nuclear Astrophysics.
Abstract: We have measured the scintillation and ionization yield of recoiling nuclei in liquid argon as a function of applied electric field by exposing a dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy pulsed narrow band neutron beam produced at the Notre Dame Institute for Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged to detect and identify neutrons scattered in the TPC and to select the energy of the recoiling nuclei. We report measurements of the scintillation yields for nuclear recoils with energies from 10.3 to 57.3 keV and for median applied electric fields from 0 to $970\text{ }\text{ }\mathrm{V}/\mathrm{cm}$. For the ionization yields, we report measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to $486\text{ }\text{ }\mathrm{V}/\mathrm{cm}$. We also report the observation of an anticorrelation between scintillation and ionization from nuclear recoils, which is similar to the anticorrelation between scintillation and ionization from electron recoils. Assuming that the energy loss partitions into excitons and ion pairs from $^{83m}\mathrm{Kr}$ internal conversion electrons is comparable to that from $^{207}\mathrm{Bi}$ conversion electrons, we obtained the numbers of excitons (${N}_{\text{ex}}$) and ion pairs (${N}_{\mathrm{i}}$) and their ratio (${N}_{\text{ex}}/{N}_{\mathrm{i}}$) produced by nuclear recoils from 16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in LAr-TPC signals due to columnar recombination, a comparison of the light and charge yield of recoils parallel and perpendicular to the applied electric field is presented for the first time.
TL;DR: In this paper, the authors describe the current understanding of the interaction between geospheres from a complex set of physical and chemical processes under the influence of ionization, and demonstrate the synergy between the evolution of thermal and electromagnetic anomalies in the Earth's atmosphere, ionosphere, and magnetosphere.
Abstract: This paper describes the current understanding of the interaction between geospheres from a complex set of physical and chemical processes under the influence of ionization. The sources of ionization involve the Earth’s natural radioactivity and its intensification before earthquakes in seismically active regions, anthropogenic radioactivity caused by nuclear weapon testing and accidents in nuclear power plants and radioactive waste storage, the impact of galactic and solar cosmic rays, and active geophysical experiments using artificial ionization equipment. This approach treats the environment as an open complex system with dissipation, where inherent processes can be considered in the framework of the synergistic approach. We demonstrate the synergy between the evolution of thermal and electromagnetic anomalies in the Earth’s atmosphere, ionosphere, and magnetosphere. This makes it possible to determine the direction of the interaction process, which is especially important in applications related to short-term earthquake prediction. That is why the emphasis in this study is on the processes proceeding the final stage of earthquake preparation; the effects of other ionization sources are used to demonstrate that the model is versatile and broadly applicable in geophysics.
TL;DR: In this paper, a two-color circularly polarized laser field was used to probe electron trajectories that are driven in a 2D plane, thus separating the tunneling angle from the rescattering angle.
Abstract: Strong-field ionization provides fundamental insight into light-matter interactions, encoding the structure of atoms and molecules on the sub\aa{}ngstr\"om and subfemtosecond scales. In this Rapid Communication, we explore an important regime: strong-field ionization by two-color circularly polarized laser fields. In contrast to past work using linearly polarized drivers, we probe electron trajectories that are driven in a two-dimensional plane, thus separating the tunneling angle from the rescattering angle. This allows us to make several findings. First, we observe a single-lobed electron distribution for co-rotating fields, and a three-lobed distribution for counter-rotating fields, providing experimental validation of the theoretical model explaining the generation of circularly polarized high harmonic light. Second, we discover that there is significant electron-ion rescattering using counter-rotating fields, but not with co-rotating fields. Finally, we show that the rescattered electrons are well separated from the directly ionized electrons, in striking contrast to similar low-energy structures seen with linearly polarized fields. These findings help overcome the long-standing problem of how to decouple the tunneling and rescattering steps in strong-field ionization, which will enable new dynamic probes of atomic and molecular structure.
TL;DR: Experimental observations of the self-truncated ionization injection scenario in centimeter-long plasma leading to the generation of narrow energy-spread GeV electron beams demonstrate its robustness and scalability and is therefore promising for practical applications.
Abstract: Ionization-induced injection mechanism was introduced in 2010 to reduce the laser intensity threshold for controllable electron trapping in laser wakefield accelerators (LWFA). However, usually it generates electron beams with continuous energy spectra. Subsequently, a dual-stage target separating the injection and acceleration processes was regarded as essential to achieve narrow energy-spread electron beams by ionization injection. Recently, we numerically proposed a self-truncation scenario of the ionization injection process based upon overshooting of the laser-focusing in plasma which can reduce the electron injection length down to a few hundred micrometers, leading to accelerated beams with extremely low energy-spread in a single-stage. Here, using 100 TW-class laser pulses we report experimental observations of this injection scenario in centimeter-long plasma leading to the generation of narrow energy-spread GeV electron beams, demonstrating its robustness and scalability. Compared with the self-injection and dual-stage schemes, the self-truncated ionization injection generates higher-quality electron beams at lower intensities and densities, and is therefore promising for practical applications.
TL;DR: A detailed review of hollow cathode discharges can be found in this paper, where the authors describe the structure of a parallel-plate discharge, particularly the gas phase and cathode surface excitation and ionization collision processes.
13 Oct 2015
TL;DR: In this article, a study of X-ray ionization of MHD accretion-disk winds in an effort to constrain the physics underlying the highly ionized ultra-fast outflows (UFOs) inferred by Xray absorbers often detected in various sub classes of Seyfert active galactic nuclei (AGNs).
Abstract: We present a study of X-ray ionization of MHD accretion-disk winds in an effort to constrain the physics underlying the highly ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption-line spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds to model the absorption features in an XMM-Newton/EPIC spectrum of the narrow-line Seyfert, PG 1211+143. We find, through identifying the detected features with Fe Kα transitions, that the absorber has a characteristic ionization parameter of log (ξc[erg cm s−1]) 5–6 and a column density on the order of NH 1023 cm−2 outflowing at a characteristic velocity of vc/c 0.1–0.2 (where c is the speed of light). The best-fit model favors its radial location at rc 200 Ro (Ro is the black hole's innermost stable circular orbit), with an inner wind truncation radius at Rt 30 Ro. The overall K-shell feature in the data is suggested to be dominated by Fe xxv with very little contribution from Fe xxvi and weakly ionized iron, which is in good agreement with a series of earlier analyses of the UFOs in various AGNs, including PG 1211+143.
TL;DR: X-ray-initiated isomerization of acetylene, a model for proton dynamics in hydrocarbons, is studied to conclude that significant proton motion occurs on a timescale comparable to the Auger relaxation that refills the K-shell vacancy.
Abstract: Proton migration in the acetylene cation is commonly used as a model to study isomerisation dynamics. Here, the authors use X-ray pump-probe experiments to study this process, and show that isomerization occurs significantly faster than expected—within the first 12 femtoseconds following core ionization.
TL;DR: Intensity studies reveal dissociative ionization as the origin of the observed PECD effect, whereas ionization of the intermediate resonance is dominating the signal.
Abstract: Photoelectron circular dichroism (PECD) is a CD effect up to the ten-percent regime and shows contributions from higher-order Legendre polynomials when multiphoton ionization is compared to single-photon ionization. We give a full account of our experimental methodology for measuring the multiphoton PECD and derive quantitative measures that we apply on camphor, fenchone and norcamphor. Different modulations and amplitudes of the contributing Legendre polynomials are observed despite the similarity in chemical structure. In addition, we study PECD for elliptically polarized light employing tomographic reconstruction methods. Intensity studies reveal dissociative ionization as the origin of the observed PECD effect, whereas ionization of the intermediate resonance is dominating the signal. As a perspective, we suggest to make use of our tomographic data as an experimental basis for a complete photoionization experiment and give a prospect of PECD as an analytic tool.
TL;DR: The work expands its application scope of g-C3N4 nanosheets and provides an alternative approach for small molecules and shows free matrix background interference and increased signal intensity in the analysis of amino acids, nucleobases, peptides, bisphenols (BPs), and nitropolycyclic aromatic hydrocarbons (nitro-PAHs).
Abstract: Ultrathin graphitic carbon nitride (g-C3N4) nanosheets served as a novel matrix for the detection of small molecules by negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was described for the first time. In comparison with conventional organic matrices and graphene matrix, the use of g-C3N4 nanosheet matrix showed free matrix background interference and increased signal intensity in the analysis of amino acids, nucleobases, peptides, bisphenols (BPs), and nitropolycyclic aromatic hydrocarbons (nitro-PAHs). A systematic comparison of g-C3N4 nanosheets with positive and negative ion modes revealed that mass spectra produced by g-C3N4 nanosheets in negative ion mode were featured by singly deprotonated ion without matrix interference, which was rather different from the complicated alkali metal complexes in positive ion mode. Good salt tolerance and reproducibility allowed the determination of 1-nitropyrene (1-NP) in sewage, and its corresponding detecti...
26 Oct 2015
TL;DR: The ionization dynamics in geometrically symmetric parallel plate capacitively coupled plasmas driven by radio frequency tailored voltage waveforms is investigated using phase resolved optical emission spectroscopy (PROES) and particle-in-cell (PIC) simulations.
Abstract: The ionization dynamics in geometrically symmetric parallel plate capacitively coupled plasmas driven by radio frequency tailored voltage waveforms is investigated using phase resolved optical emission spectroscopy (PROES) and particle-in-cell (PIC) simulations. Temporally asymmetric waveforms induce spatial asymmetries and offer control of the spatiotemporal dynamics of electron heating and associated ionization structures. Sawtooth waveforms with different rise and fall rates are employed using truncated Fourier series approximations of an ideal sawtooth. Experimental PROES results obtained in argon plasmas are compared with PIC simulations, showing excellent agreement. With waveforms comprising a fast voltage drop followed by a slower rise, the faster sheath expansion in front of the powered electrode causes strongly enhanced ionization in this region. The complementary waveform causes an analogous effect in front of the grounded electrode.
TL;DR: An improved energy-loss model for the excitation and ionization of liquid water by low-energy electrons by using the Emfietzoglou model dielectric response function used in the geant4-DNA existing model.
Abstract: Purpose: The GEANT4-DNA physics models are upgraded by a more accurate set of electron cross sections for ionization and excitation in liquid water. The impact of the new developments on low-energy electron transport simulations by the GEANT4 Monte Carlo toolkit is examined for improving its performance in dosimetry applications at the subcellular and nanometer level. Methods: The authors provide an algorithm for an improved implementation of the Emfietzoglou model dielectric response function of liquid water used in the GEANT4-DNA existing model. The algorithm redistributes the imaginary part of the dielectric function to ensure a physically motivated behavior at the binding energies, while retaining all the advantages of the original formulation, e.g., the analytic properties and the fulfillment of the f-sum-rule. In addition, refinements in the exchange and perturbation corrections to the Born approximation used in the GEANT4-DNA existing model are also made. Results: The new ionization and excitation cross sections are significantly different from those of the GEANT4-DNA existing model. In particular, excitations are strongly enhanced relative to ionizations, resulting in higher W-values and less diffusive dose-point-kernels at sub-keV electron energies. Conclusions: An improved energy-loss model for the excitation and ionization of liquid water by low-energy electrons has been implementedmore » in GEANT4-DNA. The suspiciously low W-values and the unphysical long tail in the dose-point-kernel have been corrected owing to a different partitioning of the dielectric function.« less
TL;DR: Measurements of single-photon ionization time delays between the outermost valence electrons of argon and neon are presented using a coincidence detection technique that allows for the simultaneous measurement of both species under identical conditions.
Abstract: We present measurements of single-photon ionization time delays between the outermost valence electrons of argon and neon using a coincidence detection technique that allows for the simultaneous measurement of both species under identical conditions. The analysis of the measured traces reveals energy-dependent time delays of a few tens of attoseconds with high energy resolution. In contrast to photoelectrons ejected through tunneling, single-photon ionization can be well described in the framework of Wigner time delays. Accordingly, the overall trend of our data is reproduced by recent Wigner time delay calculations. However, besides the general trend we observe resonance features occurring at specific photon energies. These features have been qualitatively reproduced and identified by a calculation using the multiconfigurational Hartree-Fock method, including the influence of doubly excited states and ionization thresholds.
TL;DR: In this paper, the abundances of electrons and ions in the hot (> 500 K), dusty parts of protoplanetary disks, treating for the first time the effects of thermionic and ion emission from the dust grains.
Abstract: We calculate the abundances of electrons and ions in the hot (> 500 K), dusty parts of protoplanetary disks, treating for the first time the effects of thermionic and ion emission from the dust grains. High-temperature ionization modeling has involved simply assuming that alkali elements such as potassium occur as gas-phase atoms and are collisionally ionized following the Saha equation. We show that the Saha equation often does not hold, because free charges are produced by thermionic and ion emission and destroyed when they stick to grain surfaces. This means the ionization state depends not on the first ionization potential of the alkali atoms, but rather on the grains' work functions. The charged species' abundances typically rise abruptly above about 800 K, with little qualitative dependence on the work function, gas density, or dust-to-gas mass ratio. Applying our results, we find that protoplanetary disks' dead zone, where high diffusivities stifle magnetorotational turbulence, has its inner edge located where the temperature exceeds a threshold value ~1000 K. The threshold is set by ambipolar diffusion except at the highest densities, where it is set by Ohmic resistivity. We find that the disk gas can be diffusively loaded onto the stellar magnetosphere at temperatures below a similar threshold. We investigate whether the "short-circuit" instability of current sheets can operate in disks and find that it cannot, or works only in a narrow range of conditions; it appears not to be the chondrule formation mechanism. We also suggest that thermionic emission is important for determining the rate of Ohmic heating in hot Jupiters.
TL;DR: An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented in this paper, where the authors investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes.
Abstract: An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (12 eV) to 310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system Semi-conductors and dielectrics materials, in bulk or thin film forms, in a range of bandgap from 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon energy A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the
TL;DR: In this article, different mechanisms of CO2 dissociation, in discharge and post-discharge conditions, have been computed by performing a parametric numerical solution of the electron Boltzmann equation as a function of the electric field, the ionization degree and the vibrational temperatures.
Abstract: Different mechanisms of CO2 dissociation, in discharge and post-discharge conditions, have been computed by performing a parametric numerical solution of the electron Boltzmann equation as a function of the electric field, the ionization degree and the vibrational temperatures and by considering elastic, inelastic, superelastic and electron electron collisions. Emphasis is given to the role of superelastic electronic and vibrational collisions in affecting the electron energy distribution function and relevant rates. The results show that, at low E/N values, the dissociation rates from pure vibrational mechanism can overcome the corresponding rates of electron impact dissociation. In any case, the electron impact dissociation rates are largely dependent on the transitions from excited vibrational levels.
TL;DR: In this paper, the deuteration and ionization structure of the DM Tau disk via interferometric observations and modelling of the key molecular ions, HCO+ and DCO+ was studied.
Abstract: Aims. We study the deuteration and ionization structure of the DM Tau disk via interferometric observations and modelling of the key molecular ions, HCO+ and DCO+ .Methods. The Plateau de Bure Array is used to observe DM Tau in lines of HCO+ (1−0), (3−2) and DCO+ (3−2) with a ~ 1.5′′ angular and ~0.2 km s-1 spectral resolution. Using a power-law fitting approach the observed column densities profiles are derived and thus the isotopic ratio R D = DCO+ /HCO+ . Chemical modelling allowed an exploration of the sensitivity of HCO+ and DCO+ abundances to physical parameters out with temperature. A steady state approximation was employed to observationally constrain the ionization fraction x (e− ).Results. Fitting of radiative transfer models suggests that there is a chemical hole in HCO+ and DCO+ , extending up to 50 AU from the star. More work is required to discern the cause of this. The observed column densities of HCO+ and DCO+ at 100 AU were (9.8+0.3 -0.7 ) × 1012 and (1.2 ± 0.7) × 1012 cm-2 respectively. Where both HCO+ and DCO+ were present, R D was found to increase radially from 0.1 at 50 AU to 0.2 at 450 AU. This behaviour was well reproduced by the chemical model. The X-ray luminosity of the central star, the interstellar UV and CO depletion were found to be the most important physical parameters controlling the abundances of HCO+ and DCO+ . Differences in the vertical extent of HCO+ and DCO+ molecular layers resulted in different responses to changing physical parameters, manifesting as radial gradients in R D . The ionization fraction was found to be x (e− ) ~ 10-7 in the molecular layer, comparable to the disk averaged value. Modelling shows that while HCO+ is the most dominant charged molecular ion in our disk model, atomic ions, such as C+ , S+ , H+ , Na+ and Mg+ , dominate the charge in both the molecular layer and disk atmosphere.Conclusions. A high value of R D is indicative of continued deuterium fractionation in a protoplanetary disk after pre/protostellar phases. Radial properties of R D can be employed to discern the importance of ionization from X-rays and UV, thus necessitating the need for more, high resolution observations of DCO+ and other deuterated species in disks. A steady-state approach commonly adopted for constraining ionization degree in prestellar cores is not applicable for disks where accurate determination of the ionization fraction in the molecular layer requires knowledge of the atomic ions present as molecular ions are relatively sparse.
TL;DR: Experimental results show that the energy spread can be reduced down to 10 MeV and that the beam energy can be tuned by varying the position of the shock.
Abstract: Ionization injection is a simple and efficient method to trap an electron beam in a laser plasma accelerator. Yet, because of a long injection length, this injection technique leads generally to the production of large energy spread electron beams. Here, we propose to use a shock front transition to localize the injection. Experimental results show that the energy spread can be reduced down to 10 MeV and that the beam energy can be tuned by varying the position of the shock. This simple technique leads to very stable and reliable injection even for modest laser energy. It should therefore become a unique tool for the development of laser-plasma accelerators.
TL;DR: In this article, the fingerprint emissions of molecules in strong laser fields are discussed based on the understanding of strong-field-molecule interactions in atmospheric as well as in vacuum environments.
Abstract: Recent studies have demonstrated that femtosecond laser pulses have high potential in application to environmental science. Because of the properties of ultrafast, broadband and high power, the propagation of femtosecond laser pulses in air can lead to the generation of a strong field of 1013–1014 W/cm2 with a large distance range from meter to kilometers. The strong laser field induces ionization and fragmentation of molecules in the laser propagation path, resulting in characteristic fingerprint emissions. This paper mainly focuses on recent research advances in environmental sensing by using femtosecond laser pulses through strong-field-induced ionization and fragmentation of molecules. The fingerprint emissions of molecules in strong laser fields are discussed based on the understanding of strong-field–molecule interactions in atmospheric as well as in vacuum environments. This is followed by a comprehensive review of several recently developed optical methods for coherent control of fingerprint emissions of molecules. Lastly, both current challenges and a future perspective of this dynamic field are discussed.