Showing papers on "Ionization published in 2006"

Cross Sections for Electron Collisions with Nitrogen Molecules

Abstract: Cross section data have been compiled for electron collisions with nitrogen molecules, based on 104 references. Cross sections are collected and reviewed for: total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational, and electronic states, dissociation, ionization, and emission of radiation. For each process, the recommended values of the cross section are presented for use. The literature has been surveyed through the end of 2003.

Probing Proton Dynamics in Molecules on an Attosecond Time Scale

Abstract: We demonstrate a technique that uses high-order harmonic generation in molecules to probe nuclear dynamics and structural rearrangement on a subfemtosecond time scale. The chirped nature of the electron wavepacket produced by laser ionization in a strong field gives rise to a similar chirp in the photons emitted upon electron-ion recombination. Use of this chirp in the emitted light allows information about nuclear dynamics to be gained with 100-attosecond temporal resolution, from excitation by an 8-femtosecond pulse, in a single laser shot. Measurements on molecular hydrogen and deuterium agreed well with calculations of ultrafast nuclear dynamics in the H2+ molecule, confirming the validity of the method. We then measured harmonic spectra from CH4 and CD4 to demonstrate a few-femtosecond time scale for the onset of proton rearrangement in methane upon ionization.

Control of Electron Localization in Molecular Dissociation

Abstract: We demonstrated how the subcycle evolution of the electric field of light can be used to control the motion of bound electrons. Results are presented for the dissociative ionization of deuterium molecules (D2 ⇒ D+ + D), where asymmetric ejection of the ionic fragment reveals that light-driven intramolecular electronic motion before dissociation localizes the electron on one of the two D+ ions in a controlled way. The results extend subfemtosecond electron control to molecules and provide evidence of its usefulness in controlling reaction dynamics.

Dynamics of an atmospheric pressure plasma plume generated by submicrosecond voltage pulses

Abstract: Nonequilibrium plasmas driven by submicrosecond high voltage pulses have been proven to produce high-energy electrons, which in turn lead to enhanced ionization and excitations. Here, we describe a device capable of launching a cold plasma plume in the surrounding air. This device, “the plasma pencil,” is driven by few hundred nanosecond wide pulses at repetition rates of a few kilohertz. Correlation between current-voltage characteristics and fast photography shows that the plasma plume is in fact a small bulletlike volume of plasma traveling at unusually high velocities. A model based on photoionization is used to explain the propagation kinetics of the plasma bullet under low electric field conditions.

Above-threshold ionization by few-cycle pulses

Abstract: The theoretical description and the experimental methods and results for above-threshold ionization (ATI) by few-cycle pulses are reviewed. A pulse is referred to as a few-cycle pulse if its detailed shape, parametrized by its carrier-envelope phase, affects its interaction with matter. Angular-resolved ATI spectra are analysed with the customary strong-field approximation (SFA) as well as the numerical solution of the time-dependent Schrodinger equation (TDSE). After a general discussion of the characteristics and the description of few-cycle pulses, the behaviour of the ATI spectrum under spatial inversion is related to the shape of the laser field. The ATI spectrum both for the direct and for the rescattered electrons in the context of the SFA is evaluated by numerical integration and by the method of steepest descent (saddle-point integration), and the results are compared. The saddle-point method is modified to avoid the singularity of the dipole transition matrix element at the steepest-descent times. With the help of the saddle-point method and its classical limit, namely the simple-man model, the various features of the ATI spectrum, their behaviour under inversion, the cut-offs and the presence or absence of ATI peaks are analysed as a function of the carrier-envelope phase of the few-cycle laser field. All features observed in the spectra can be explained in terms of a few quantum orbits and their superposition. The validity of the SFA and the concept of quantum orbits are established by comparing the ATI spectra with those obtained numerically from the ab initio solution of the TDSE.

The Ionization Constant of Water over Wide Ranges of Temperature and Density

Abstract: A semitheoretical approach for the ionization constant of water, KW, is used to fit the available experimental data over wide ranges of density and temperature. Statistical thermodynamics is employed to formulate a number of contributions to the standard state chemical potential of the ionic hydration process. A sorption model is developed for calculating the inner-shell term, which accounts for the ion–water interactions in the immediate ion vicinity. A new analytical expression is derived using the Bragg–Williams approximation that reproduces the dependence of a mean ion solvation number on the solvent chemical potential. The proposed model was found to be correct at the zero-density limit. The final formulation has a simple analytical form, includes seven adjustable parameters, and provides good fitting of the collected KW data, within experimental uncertainties, for a temperature range of 0–800 °C and densities of 0–1.2 g cm−3.

Ion formation mechanisms in UV-MALDI

Abstract: Matrix Assisted Laser Desorption/Ionization (MALDI) is a very widely used analytical method, but has been developed in a highly empirical manner. Deeper understanding of ionization mechanisms could help to design better methods and improve interpretation of mass spectra. This review summarizes current mechanistic thinking, with emphasis on the most common MALDI variant using ultraviolet laser excitation. A two-step framework is gaining acceptance as a useful model for many MALDI experiments. The steps are primary ionization during or shortly after the laser pulse, followed by secondary reactions in the expanding plume of desorbed material. Primary ionization in UV-MALDI remains somewhat controversial, the two main approaches are the cluster and pooling/photoionization models. Secondary events are less contentious, ion–molecule reaction thermodynamics and kinetics are often invoked, but details differ. To the extent that local thermal equilibrium is approached in the plume, the mass spectra may be straightforwardly interpreted in terms of charge transfer thermodynamics.

Springer handbook of atomic, molecular, and optical physics

Abstract: Units and Constants- Part A Mathematical Methods: Angular Momentum Theory- Group Theory for Atomic Shells- Dynamical Groups- Perturbation Theory- Second Quantization- Density Matrices- Computational Techniques- Hydrogenic Wave Functions- Part B Atoms: Atomic Spectroscopy- High Precision Calculations for Helium- Atomic Multipoles- Atoms in Strong Fields- Rydberg Atoms- Rydberg Atoms in Strong Static Fields- Hyperfine Structure- Precision Oscillator Strength and Lifetime Measurements- Ion Beam Spectroscopy- Line Shapes and Radiation Transfer- Thomas - Fermi and Other Density-Functional Theories- Atomic Structure: Multiconfiguration Hartree - Fock Theories- Relativistic Atomic Structure- Many-Body Theory of Atomic Structure and Processes- Photoionization of Atoms- Autoionization- Green's Functions of Field Theory- Quantum Electrodynamics- Tests of Fundamental Physics- Parity Nonconserving Effects in Atoms- Atomic Clocks and Constraints on Variations of Fundamental Constants- Molecular Structure- Molecular Symmetry and Dynamics- Radiative Transition Probabilities- Molecular Photodissociation- Time-Resolved Molecular Dynamics- Nonreactive Scattering- Gas Phase Reactions- Gas Phase Ionic Reactions- Clusters- Infrared Spectroscopy- Laser Spectroscopy in the Submillimeter and Far-Infrared Region- Spectroscopic Techniques: Lasers- Spectroscopic Techniques: Cavity-Enhanced Methods- Spectroscopic Techniques: Ultraviolet- Part C Scattering Theory: Elastic Scattering: Classical, Quantal, and Semiclassical- Orientation and Alignment in Atomic and Molecular Collisions- Electron-Atom, Electron-Ion, and Electron-Molecule Collisions- Positron Collisions- Adiabatic and Diabatic Collision Processes at Low Energies- Ion -Atom and Atom - Atom Collisions- Ion - Atom Charge Transfer Reactions at Low Energies- Continuum Distorted-Wave and Wannier Methods- Ionization in High Energy Ion - Atom Collisions- Electron - Ion and Ion - Ion Recombination- Dielectronic Recombination- Rydberg Collisions: Binary Encounter, Born and Impulse Approximations- Mass Transfer at High Energies: Thomas Peak- Classical Trajectory and Monte Carlo Techniques- Collisional Broadening of Spectral Lines- Part D Scattering Experiments: Photodetachment- Photon - Atom Interactions: Low Energy- Photon - Atom Interactions: Intermediate Energies- Electron - Atom and Electron - Molecule Collisions- Ion - Atom Scattering Experiments: Low Energy- Ion - Atom Collisions:High Energy- Reactive Scattering- Ion - Molecule Reactions- Part E Quantum Optics: Light - Matter Interaction- Absorption and Gain Spectra- Laser Principles- Types of Lasers- Nonlinear Optics- Coherent Transients- Multiphoton and Strong-Field Processes- Cooling and Trapping- Quantum Degenerate Gases: Bose - Einstein Condensation- De Broglie Optics- Quantized Field Effects- Entangled Atoms and Fields: Cavity QED- Quantum Optical Tests of the Foundations of Physics- Quantum Information- Part F Applications: Applications of Atomic and Molecular Physics to Astrophysics- Comets- Aeronomy- Applications of Atomic and Molecular Physics to Global Change- Atoms in Dense Plasmas- Conduction of Electricity in Gases- Applications to Combustion- Surface Physics- Interface with Nuclear Physics- Charged-Particle - Matter Interactions- Radiation Physics- About the Authors- Subject Index

An electronic time scale in chemistry

Abstract: Ultrafast, subfemtosecond charge migration in small peptides is discussed on the basis of computational studies and compared with the selective bond dissociation after ionization as observed by Schlag and Weinkauf. The reported relaxation could be probed in real time if the removal of an electron could be achieved on the attosecond time scale. Then the mean field seen by an electron would be changing rapidly enough to initiate the migration. Tyrosine-terminated tetrapeptides have a particularly fast charge migration where in <1 fs the charge arrives at the other end. A femtosecond pulse can be used to observe the somewhat slower relaxation induced by correlation between electrons of different spins. A slower relaxation also is indicated when removing a deeper-lying valence electron. When a chromophoric amino acid is at one end of the peptide, the charge can migrate all along the peptide backbone up to the N end, but site-selective ionization is probably easier to detect for tryptophan than for tyrosine.

Droplet Dynamics and Ionization Mechanisms in Desorption Electrospray Ionization Mass Spectrometry

Abstract: A droplet pickup and other mechanisms have been suggested for the ionization of biomolecules like peptides and proteins by desorption electrospray ionization To verify this hypothesis phase Doppler particle analysis was used to study the sizes and velocities of droplets involved in DESI It was found that impacting droplets typically have velocities of 120 m/s and average diameters of 2−4 μm Small differences in sprayer construction influence the operating conditions at which droplets of these dimensions are produced Under these conditions, the kinetic energy per impacting water molecule is less than 06 meV and sputtering through momentum transfer during collisions or ionization by other electronic processes is unlikely Droplets arrive at the surface with velocities well below the speed of sound in common materials, thereby excluding the possibility of ionization by shockwave formation Some droplets appear to roll along the surface, increasing contact time and presumably the amount of material that

Monte Carlo model for analysis of thermal runaway electrons in streamer tips in transient luminous events and streamer zones of lightning leaders

Abstract: [1] Streamers are thin filamentary plasmas that can initiate spark discharges in relatively short (several centimeters) gaps at near ground pressures and are also known to act as the building blocks of streamer zones of lightning leaders. These streamers at ground pressure, after 1/N scaling with atmospheric air density N, appear to be fully analogous to those documented using telescopic imagers in transient luminous events (TLEs) termed sprites, which occur in the altitude range 40–90 km in the Earth's atmosphere above thunderstorms. It is also believed that the filamentary plasma structures observed in some other types of TLEs, which emanate from the tops of thunderclouds and are termed blue jets and gigantic jets, are directly linked to the processes in streamer zones of lightning leaders. Acceleration, expansion, and branching of streamers are commonly observed for a wide range of applied electric fields. Recent analysis of photoionization effects on the propagation of streamers indicates that very high electric field magnitudes ∼10 Ek, where Ek is the conventional breakdown threshold field defined by the equality of the ionization and dissociative attachment coefficients in air, are generated around the tips of streamers at the stage immediately preceding their branching. This paper describes the formulation of a Monte Carlo model, which is capable of describing electron dynamics in air, including the thermal runaway phenomena, under the influence of an external electric field of an arbitrary strength. Monte Carlo modeling results indicate that the ∼10 Ek fields are able to accelerate a fraction of low-energy (several eV) streamer tip electrons to energies of ∼2–8 keV. With total potential differences on the order of tens of MV available in streamer zones of lightning leaders, it is proposed that during a highly transient negative corona flash stage of the development of negative stepped leader, electrons with energies 2–8 keV ejected from streamer tips near the leader head can be further accelerated to energies of hundreds of keV and possibly to several tens of MeV, depending on the particular magnitude of the leader head potential. It is proposed that these energetic electrons may be responsible (through the “bremsstrahlung” process) for the generation of hard X rays observed from ground and satellites preceding lightning discharges or with no association with lightning discharges in cases when the leader process does not culminate in a return stroke. For a lightning leader carrying a current of 100 A, an initial flux of ∼2–8 keV thermal runaway electrons integrated over the cross-sectional area of the leader is estimated to be ∼1018 s−1, with the number of electrons accelerated to relativistic energies depending on the particular field magnitude and configuration in the leader streamer zone during the negative corona flash stage of the leader development. These thermal runaway electrons could provide an alternate source of relativistic seed electrons which were previously thought to require galactic cosmic rays. The duration of the negative corona flash and associated energetic radiation is estimated to be in the range from ∼1 μs to ∼1 ms depending mostly on the pressure-dependent size of the leader streamer zone.

Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

Abstract: The optical excitation and thermal ionization energies of oxygen vacancies in m-HfO2 are calculated using a non-local density functional theory with atomic basis sets and periodic supercell. The thermal ionization energies of negatively charged V- and V2- centers are consistent with values obtained by the electrical measurements. The results suggest that negative oxygen vacancies are essentially polaronic in origin. They are likely candidates for intrinsic shallow electron traps in the hafnium based gate stack devices. (c) 2006 American Institute of Physics.

The galactic cosmic ray ionization rate

Abstract: The chemistry that occurs in the interstellar medium in response to cosmic ray ionization is summarized, and a review of the ionization rates that have been derived from measurements of molecular abundances is presented. The successful detection of large abundances of H3+ in diffuse clouds and the recognition that dissociative recombination of H3+ is fast has led to an upward revision of the derived ionization rates. In dense clouds the molecular abundances are sensitive to the depletion of carbon monoxide, atomic oxygen, nitrogen, water, and metals and the presence of large molecules and grains. Measurements of the relative abundances of deuterated species provide information about the ion removal mechanisms, but uncertainties remain. The models, both of dense and diffuse clouds, that are used to interpret the observations may be seriously inadequate. Nevertheless, it appears that the ionization rates differ in dense and diffuse clouds and in the intercloud medium.

Dipole Blockade at Förster Resonances in High Resolution Laser Excitation of Rydberg States of Cesium Atoms

Abstract: High resolution laser excitation of $np$ Rydberg states of cesium atoms shows a dipole blockade at F\"orster resonances corresponding to the resonant dipole-dipole energy transfer of the $np+np\ensuremath{\rightarrow}ns+(n+1)s$ reaction. The dipole-dipole interaction can be tuned on and off by the Stark effect, and such a process, observed for relatively low $n(25--41)$, is promising for quantum gate devices. Both Penning ionization and saturation in the laser excitation can limit the range of observation of the dipole blockade.

Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods

Abstract: Recently developed correlation consistent basis sets for the first row transition metal elements Sc–Zn have been utilized to determine complete basis set (CBS) scalar relativistic electron affinities, ionization potentials, and 4s23dn−2–4s1dn−1 electronic excitation energies with single reference coupled cluster methods [CCSD(T), CCSDT, and CCSDTQ] and multireference configuration interaction with three reference spaces: 3d4s, 3d4s4p, and 3d4s4p3d′. The theoretical values calculated with the highest order coupled cluster techniques at the CBS limit, including extrapolations to full configuration interaction, are well within 1kcal∕mol of the corresponding experimental data. For the early transition metal elements (Sc-Mn) the internally contracted multireference averaged coupled pair functional method yielded excellent agreement with experiment; however, the atomic properties for the late transition metals (Mn-Zn) proved to be much more difficult to describe with this level of theory, even with the largest ...

On the ionisation fraction in protoplanetary disks. I. Comparing different reaction networks

Abstract: We calculate the ionisation fraction in protostellar disk models using a number of different chemical reaction networks, including gas-phase and gas-grain reaction schemes. The disk models we consider are conventional α-disk, which include viscous heating and radiative cooling. The primary source of ionisation is assumed to be X-ray irradiation from the central star. For most calculations we adopt a specific disk model (with accretion rate M = 10 -7 M ○. yr -1 and α = 10 -2 ), and examine the predictions made by the chemical networks concerning the ionisation fraction, magnetic Reynolds number, and spatial extent of magnetically active regions. This is to aid comparison between the different chemical models. We consider a number of gas-phase chemical networks. The simplest is the five species model proposed by Oppenheimer & Dalgarno (1974). We construct more complex models by extracting species and reactions from the UMIST data base. In general we find that the simple models predict higher fractional ionisation levels and more extensive active zones than the more complex models. When heavy metal atoms are included the simple models predict that the disk is magnetically active throughout. The complex models predict that extensive regions of the disk remain magnetically uncoupled (dead) even when the fractional abundance of magnesium x Mg = 10 -8 . This is because of the large number of molecular ions that are formed, which continue to dominate the recombination with free electrons in the presence of magnesium. The addition of submicron sized grains with a concentration of x gr = 10 -12 causes the size of the dead zone to increase dramatically for all kinetic models considered, as the grains are highly efficient at sweeping up the free electrons. We find that the simple and complex gas-grain reaction schemes agree on the size and structure of the resulting dead zone, as the grains play a dominant role in determining the ionisation fraction. We examine the effects of depleting the concentration of small grains as a crude means of modeling the growth of grains during planet formation. We find that a depletion factor of 10 -4 causes the gas-grain chemistry to converge to the gas-phase chemistry when heavy metals are absent. When magnesium is included a depletion factor of 10 -8 is required to reproduce the gas-phase ionisation fraction. This suggests that efficient grain growth and settling will he required in protoplanetary disks, before a substantial fraction of the disk mass in the planel forming zone between 1-10 AU becomes magnetically active and turbulent. Only after this has occurred can gas-phase chemical models be used to predict reliably the ionisation degree in protoplanetary disks.

Cosmic ray induced ionization in the atmosphere: Full modeling and practical applications

Abstract: [1] We present a physical model to calculate cosmic ray induced ionization in the atmosphere. The model is based on the Monte Carlo CORSIKA tool, which simulates full development of an electromagnetic-muon-nucleonic cascade in the atmosphere, with the FLUKA package used for low-energy interactions. The direct ionization by primary cosmic rays is explicitly taken into account. The model is applicable to the entire atmosphere, from the ground up to the stratosphere. A comparison to fragmentary direct measurements of the ionization in the atmosphere confirms the validity of the model in the whole range of geographical latitudes and altitudes. Results of the full Monte Carlo simulation are tabulated in a form of the ionization yield function. These tables are given together with a detailed recipe, which allows a user to compute easily the cosmic ray induced ionization for given location, altitude and the spectrum of cosmic rays. This provides a new tool for a quantitative study of the space weather influence upon the Earth's environment. Some practical applications are discussed.

Radiative Recombination Data for Modeling Dynamic Finite-Density Plasmas

Abstract: We have calculated partial final-state resolved radiative recombination (RR) rate coefficients from the initial ground and metastable levels of all elements up to and including Zn, plus Kr, Mo, and Xe, for all isoelectronic sequences up to Na-like forming Mg-like. The data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf48, which spans a temperature range of z2(101-107) K, where z is the initial ion charge. Fits to total rate coefficients have been determined, for both the ground and metastable levels, and those for the ground are presented here. Comparison is made both with previous RR rate coefficients and with (background) R-matrix photoionization cross sections. This RR database complements a dielectronic recombination (DR) database already produced, and both are being used to produce updated ionization balances for both (electron) collisionally ionized and photoionized plasmas.

Ionization state, excited populations and emission of impurities in dynamic finite density plasmas: I. The generalized collisional-radiative model for light elements

Abstract: The paper presents an integrated view of the population structure and its role in establishing the ionization state of light elements in dynamic, finite density, laboratory and astrophysical plasmas. There are four main issues, the generalized collisional-radiative picture for metastables in dynamic plasmas with Maxwellian free electrons and its particularizing to light elements, the methods of bundling and projection for manipulating the population equations, the systematic production/use of state selective fundamental collision data in the metastable resolved picture to all levels for collisonal-radiative modelling and the delivery of appropriate derived coefficients for experiment analysis. The ions of carbon, oxygen and neon are used in illustration. The practical implementation of the methods described here is part of the ADAS Project.

A two-dimensional hybrid model of the Hall thruster discharge

Abstract: Particle-in-cell methods are used for ions and neutrals. Probabilistic methods are implemented for ionization, charge-exchange collisions, gas injection, and particle-wall interaction. A diffusive macroscopic model is proposed for the strongly magnetized electron population. Cross-field electron transport includes wall collisionality and Bohm-type diffusion, the last one dominating in most of the discharge. Plasma quasineutrality applies except for space-charge sheaths, which are modeled taking into consideration secondary-electron-emission and space-charge saturation. Specific weighting algorithms are developed in order to fulfil the Bohm condition on the ion flow at the boundaries of the quasineutral domain. The consequence is the full development of the radial plasma structure and correct values for ion losses at lateral walls. The model gains in insight and physical consistency over a previous version, but thrust efficiency is lower than in experiments, indicating that further model refinement of some phenomena is necessary.

Physics of strongly coupled plasma

Abstract: 1. NONIDEAL PLASMA. BASIC CONCEPTS 2. ELECTRICAL METHODS OF NONIDEAL PLASMA GENERATION 3. DYNAMIC METHODS IN THE PHYSICS OF NON-IDEAL PLASMA 4. IONIZATION EQUILIBRIUM AND THERMODYNAMIC PROPERTIES OF WEAKLY IONIZED PLASMAS 5. THERMODYNAMICS OF PLASMAS WITH DEVELOPED IONIZATION 6. ELECTRICAL CONDUCTIVITY OF PARTIALLY IONIZED PLASMA 7. ELECTRICAL CONDUCTIVITY OF FULLY IONIZED PLASMA 8. THE OPTICAL PROPERTIES OF DENSE PLASMA 9. METALLIZATION OF NONIDEAL PLASMAS 10. NONNEUTRAL PLASMAS 11. DUSTY PLASMAS Appendices

Radiative recombination data for modelling dynamic finite-density plasmas

Abstract: We have calculated partial final-state resolved radiative recombination (RR) rate coefficients from the initial ground and metastable levels of all elements up to and including Zn, plus Kr, Mo, and Xe, for all isoelectronic sequences up to Na-like forming Mg-like. The data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf48, which spans a temperature range of z^2(10^1 - 10^7)K, where z is the initial ion charge. Fits to total rate coefficients have been determined, for both the ground and metastable levels, and those for the ground are presented here. Comparison is made both with previous RR rate coefficients and with (background) R-matrix photoionization cross sections. This RR database complements a DR database already produced and both are being used to produce updated ionization balances for both (electron) collisionally ionized and photoionized plasmas.

The formation of massive stars: accretion, disks and the development of hypercompact HII regions

Abstract: The hypothesis that massive stars form by accretion can be investigated by simple analytical calculations that describe the effect that the formation of a massive star has on its own accretion flow. Within a simple accretion model that includes angular momentum, that of gas flow on ballistic trajectories around a star, the increasing ionization of a massive star growing by accretion produces a three-stage evolutionary sequence. The ionization first forms a small quasi-spherical HII region gravitationally trapped within the accretion flow. At this stage the flow of ionized gas is entirely inward. As the ionization increases, the HII region transitions to a bipolar morphology in which the inflow is replaced by outflow within a narrow range of angle with about the bipolar axis. At higher rates of ionization, the opening angle of the outflow region progressively increases. Eventually, in the third stage, the accretion is confined to a thin region about an equatorial disk. Throughout this early evolution, the HII region is of hypercompact to ultracompact size depending on the mass of the enclosed star or stars. These small HII regions whose dynamics are dominated by stellar gravitation and accretion are different than compact and larger HII regions whose dynamics are dominated by the thermal pressure of the ionized gas.

Multiphoton ionization in dielectrics: comparison of circular and linear polarization.

Abstract: Ionization mechanisms in bulk dielectrics irradiated by single intense 50-fs-laser pulses are investigated by ultrafast time-resolved imaging interferometry. Polarization-sensitive 6-photon ionization is shown to be the dominant ionization mechanism in fused silica and sapphire at intensities around $10\text{ }\text{ }\mathrm{TW}/{\mathrm{cm}}^{2}$. For both materials the cross sections of 6-photon ionization are found to be significantly higher for linear polarization than for circular. Our experimental results corroborate an earlier theoretical prediction on the dominance of linear polarization in high-order multiphoton ionization.

The physical nature of thermal anomalies observed before strong earthquakes

Abstract: The paper examines the effect of air ionization on the thermal balance of the boundary layer of atmosphere. In seismically active areas the increased radon emanation from active faults and cracks before earthquakes is the primary source of air ionization. The problem is analyzed both on microscopic and macroscopic levels and in both cases the significant changes of the air relative humidity and air temperature are obtained. This happens due to the water molecules attachment to the newly formed ions (or in other words, condensation) which leads to the excretion of the latent heat. Obtained results permit us to explain the changes of the surface temperature and the surface latent heat flux increase before earthquakes observed by remote sensing satellites, as well as ground based measurements of the air temperature and relative humidity variations before the Colima earthquake (M7.6) of 2003 in Mexico, Hector Mine earthquake (M7.1) of 1999 in USA and Parkfield earthquake (M6) of 2004 in USA. These findings are also supported by the results of active experiments where the installation of artificial ionization of atmosphere is used.

Simultaneous measurement of ionization and scintillation from nuclear recoils in liquid xenon for a dark matter experiment.

Abstract: We report the first measurements of the absolute ionization yield of nuclear recoils in liquid xenon, as a function of energy and electric field. Independent experiments were carried out with two dual-phase time-projection chamber prototypes, developed for the XENON dark matter project. We find that the charge yield increases with decreasing recoil energy, and exhibits only a weak field dependence. These results are the first unambiguous demonstration of the capability of dual-phase xenon detectors to discriminate between electron and nuclear recoils down to 20 keV, a key requirement for a sensitive dark matter search.

Frequency coupling in dual frequency capacitively coupled radio-frequency plasmas

Abstract: An industrial, confined, dual frequency, capacitively coupled, radio-frequency plasma etch reactor (Exelan®, Lam Research) has been modified for spatially resolved optical measurements. Space and phase resolved optical emission spectroscopy yields insight into the dynamics of the discharge. A strong coupling of the two frequencies is observed in the emission profiles. Consequently, the ionization dynamics, probed through excitation, is determined by both frequencies. The control of plasma density by the high frequency is, therefore, also influenced by the low frequency. Hence, separate control of plasma density and ion energy is rather complex.