We present energy-resolved angular distributions of photoelectrons generated in above-threshold ionization (ATI) of nonaligned diatomic molecules N2 and O2 in high-intensity short laser pulses, with emphasis on the most energetic part of the spectra. The angular distribution for photoelectrons with energy of 10U(p) (U(p): ponderomotive energy), i.e., the ...

In this paper, experimental results are presented which clearly demonstrate the effectiveness that an external field has in altering the dissociation dynamics. The experiment examines the strong-field dissociation dynamics of molecular hydrogen ions and its deuterated isotopes. These studies involve multiphoton excitation in the intensity regime of 10[sup 11-14] W/cm[sup 2] with the fundamental ...

In this paper, experimental results are presented which clearly demonstrate the effectiveness that an external field has in altering the dissociation dynamics. The experiment examines the strong-field dissociation dynamics of molecular hydrogen ions and its deuterated isotopes. These studies involve multiphoton excitation in the intensity regime of 10{sup 11-14} W/cm{sup 2} with the fundamental ...

of the ionized electron wave packet calculated at a delay of 120 ps for ionization of Xe atoms preparedAbove-threshold ionization in a strong dc electric field Y. Ni,1 S. Zamith,1,2 F. L�pine,1 T received 3 November 2007; published 18 July 2008 High-lying Rydberg states of Xe have been ...

and the electron energy is Ee mec2 . It should be noted that this free-wave acceleration of ionized electronsAbove Threshold Ionization in Tightly Focused, Strongly Relativistic Laser Fields A. Maltsev and T September 2002; published 5 February 2003) The dynamics of electrons ionized from high ...

We present a method for the calculation of multiphoton ionization, including above-threshold ionization and autoionization, which goes beyond the one-electron approximation. We illustrate the method with examples of calculations in He and Mg.

Using a frequency-domain theory, we demonstrate that an angle-resolved high-order above-threshold ionization (HATI) spectrum carries three pieces of important information: the fingerprint of the molecular wave function in the direct above-threshold-ionization amplitude, the geometrical structure of the molecule in the potential ...

Using a frequency-domain theory, we demonstrate that an angle-resolved high-order above-threshold ionization (HATI) spectrum carries three pieces of important information: the fingerprint of the molecular wave function in the direct above-threshold-ionization amplitude, the geometrical structure of the molecule in the potential ...

A technique for calculating above-threshold bound-bound transitions of an atomic optical electron, based on the use of generalized Sturm expansion of the Green's function for a potential with a Coulomb asymptotics has been developed within the model-potential method. The dynamic polarizabilities of alkali-metal and noble gas atoms are calculated in the frequency range ...

Using a triatomic molecular model, we show that the interference pattern in the high-order above-threshold ionization (HATI) spectrum depends dramatically on the charge distribution of the molecular ion. Therefore the charge distribution can be considered a crucial factor for imaging a molecular geometric structure. Based on this study, a general ...

Using a triatomic molecular model, we show that the interference pattern in the high-order above-threshold ionization (HATI) spectrum depends dramatically on the charge distribution of the molecular ion. Therefore the charge distribution can be considered a crucial factor for imaging a molecular geometric structure. Based on this study, a general ...

Photoelectron energy spectra for ionization in a strong laser field are calculated within the Floquet framework, for a one-electron model of argon and for other model potentials. The results indicate that, at least for linear polarization and not too short pulse durations, the plateau enhancements dominating high-order above-threshold ...

Anisotropy parameters and cross section ratios of two-color two-photon above threshold ionization sidebands from argon are measured using photoelectron velocity map imaging with the selected 13th or 15th high-order harmonics in a perturbative 800 nm dressing field. A new data analysis technique determines accurate anisotropy parameters ...

When an electron from a diatomic molecule undergoes tunneling-rescattering ionization, a novel form of destructive interference can be realized that involves all four geometric orbits that are available to the electron when it is freed, because both ionization and rescattering may take place at the same or at different centers. We find experimentally and ...

High-order above-threshold ionization by few-cycle laser pulses is analyzed in terms of quantum orbits. For a given carrier-envelope phase, the number of contributing orbits and their ionization and rescattering times determine the shape of the angle-resolved spectrum in all detail. Conversely, analysis of a given spectrum reveals the ...

frequency l. Immediately after being released from the atom in the ionization event, the electron wave above-threshold ionization photoelectron peaks in the strong-field (800 nm, 60 fs, 3.6 - 9.0 � 1013 W model based on calculated field ionization rates in an intense laser field. Finally, the abundance

Ionization of atoms is the first step in many analytical procedures. The cross section for ionizing a particular atomic shell is essential for calculating the magnitude of analytical signals. Calculations using atomic wave functions for various shells of all elements relevant for X-ray microanalysis over a range of electron energies up to 400 keV were ...

The ionization of HCl by electron impact was studied in a mass spectrometer with a pseudomonoenergetic electron beam. The ionization potential of HCl was determined as 12.56 plus or minus 0.1 ev. The ionization curve at threshold exhibits excessive curvature which is attributed to the /sup 2/II/sub i/ doublet ground states ...

We explore the effects of multiple participating final ion states during strong field ionization (SFI) and high-harmonic generation (HHG) using a two-electron two-center reduced-dimensionality model. In particular, we propose to use above threshold ionization (ATI) photoelectron spectra to identify ionic states ...

Above-threshold ionization of atoms by XUV short laser pulses with frequencies close to the resonant 1s�2p transition is investigated. We present a theory based on a variational expression using trial wavefunctions for the final and the initial states. For the former we use a Coulomb�Volkov wavefunction, and for the latter a close-coupling solution of ...

In a high-intensity laser field an atom can absorb more photons than the minimum necessary for ionization. It is known as above threshold ionization (ATI). Theoretically it is the most difficult case to handle as we have to consider transitions in continuum. To study ATI we use the perturbation theory and Green's ...

-order) above-threshold ionization (HATI) [3�5], nonsequential double (and multiple) ionization and high" (QRS) theory [3,5�9]. Related treatments of HATI without the explicit factorization but which include on the rescattering, or plateau (HATI), electrons whose behavior is calculable by QRS. The major goal of this part

back to its parent ion, off which in the case of high-order above-threshold ionization HATI, this is no longer so, and the additional freedom is reflected in the HATI electron spectrum 5,8 . Laser-atom physics, we will utilize it to analyze HATI by few-cycle pulses. We concentrate on high-order above

The process of above threshold ionization by plane polarized intense radiation fields has enabled cold ionized plasmas to be created. The final temperature depends on the heating process during the laser pulse. Collisional or inverse bremsstrahlung is a major effect at high density. It is argued that under these ...

This paper discusses recent theoretical results on above threshold ionization harmonic generation and high-frequency, high intensity suppression of ionization. These studies of multiphoton processes in atoms and molecules for short, intense pulsed optical lasers have been carried out using techniques which involve ...

We have calculated the two-photon above-threshold-ionization cross sections of rare-gas atoms by extreme ultraviolet (xuv) photons in the extended framework of multichannel quantum defect theory. Since free-free dipole moments do not converge in the length gauge, we have made the combined use of the length gauge for small r and the acceleration gauge for large r. The ...

Energy-dependent photoelectron angular distributions from two-color two-photon above threshold ionizations are investigated to determine the partial-wave characteristics of free-free electronic transitions in helium. Sideband photoelectron energies ranging from 0.18 to 13.0 eV are measured with different wavelengths of the perturbative ...

We investigate the cutoff law for high-order above-threshold ionization (HATI) within a semiclassical framework. By explicitly adopting the tunneling effect and considering the initial position shift of the tunneled electron from the origin in the model, the cutoff energy position in HATI spectrum exhibits a well-defined upshift from the simple-man model ...

Many nonlinear quantum phenomena of intense laser-atom physics can be intuitively explained with the concept of trajectory. In this paper, Bohmian mechanics (BM) is introduced to study a multiphoton process of atoms interacting with the intense laser field: above-threshold ionization (ATI). Quantum trajectory of an atomic electron in intense laser field is ...

Many nonlinear quantum phenomena of intense laser-atom physics can be intuitively explained with the concept of trajectory. In this paper, Bohmian mechanics (BM) is introduced to study a multiphoton process of atoms interacting with the intense laser field: above-threshold ionization (ATI). Quantum trajectory of an atomic electron in intense laser field is ...

We theoretically study a process in which helium is doubly ionized by absorbing two soft x-ray (91.45 eV) photons from attosecond, intense high-order harmonic sources. We directly solve the time-dependent Schroedinger equation and obtain electron energy distribution in the double continuum. Our results show that between the two peaks in electron energy spectra, expected for ...

We describe the results of experiments performed in Krypton to observe the effect of an isolated atomic level on harmonic generation at intensities above 10(sup 13) W/cm(sup 2). We have measured the intensity of harmonics produced as a function of laser i...

that an angle-resolved high-order above-threshold ion- ization HATI spectrum carries three pieces of important-assisted collisions. As a result all main interference features in the HATI spectrum can be physically explained-threshold ionization HATI 4�8 processes. Odzak and Milosevic 2 showed that clear minima on HHG spectra reveal molecular

laser field. High-order harmonic generation (HHG) and high- energy above-threshold ionization (HATI. In HATI, the returning electrons are backscattered by the parent ion and emerge as high have shown that both HATI and HHG spectra can be accurately calculated using the so-called quantitative

We investigate high-order above-threshold ionization (HATI) of diatomic molecules having different symmetries by an elliptically polarized laser field using the modified molecular strong-field approximation. The yields of high-energy electrons contributing to the plateau region of the photoelectron spectra strongly depend on the employed ellipticity. This ...

The large polycyclic aromatic hydrocarbon molecules coronene, benzo[GHI]perylene, and anthracene have been ionized with femtosecond laser pulses at low laser intensities and the ionization process studied with velocity map imaging spectroscopy, supplemented with ion yield measurements. The electron spectra of coronene and benzo[GHI]perylene are ...

We present molecular above-threshold ionization (MATI) spectra generated by ultrashort intense linearly and circularly polarized laser pulses from nonperturbative numerical solutions of the corresponding time-dependent Schr�dinger equation in the molecular-ion H2+. It is found that high-order MATI spectra with maximum kinetic energy 32Up, where ...

Electrons produced as a result of above-threshold ionization of high-Z atoms can be accelerated by currently producible laser pulses up to GeV energies, as shown recently in Hu and Starace, Phys. Rev. Lett. 88 (2002) Article No. 245003. To describe electron acceleration by general focused laser fields, we employ an analytical model based on a Hamiltonian, fully relativistic, ...

Measurements of energy-resolved angular distributions of electrons generated in above-threshold ionization of rare gases in a field with elliptical polarization are presented, with emphasis on the high-energy part of the spectra. The data show a second plateau at a specific angle with respect to the large component of the laser field. The results are compared to a calculation ...

We report calculations of double-ionization energy spectra and momentum distributions of laser-driven helium due to few-cycle pulses of wavelength 195 nm. The results are obtained from full-dimensional numerical integration of the two-electron time-dependent Schr�dinger equation. A momentum-space analysis of doubly ionizing wavepackets shows that the ...

In the improved strong-field approximation, which describes high-order above-threshold ionization (HATI), the rescattering of the ionized electron on the parent ion is described within the first-order Born approximation. The low-frequency approximation for laser-assisted scattering goes beyond the first Born approximation. In the ...

Two-photon above-threshold ionization (ATI) relative cross sections from the 3 {sup 1}P state of Mg have been measured using two-color ionization in the focus of a magnetic bottle spectrometer and have been calculated using the Green's-function method in the Feshbach formalism and an L{sup 2}-integrable close-coupling ...

Photoabsorption above the threshold ionization potential was observed for the photoelectron spectra of CO2 at relatively low laser intensity when resonant with several bound Rydberg states at the three-photon level. It is suggested that these results can be explained in terms of a resonance-enhanced above-threshold absorption (REATA) process in which a ...

The pulse lengths of intense few-cycle (4-10 fs) laser pulses at 790 nm are determined in real-time using a stereographic above-threshold ionization (ATI) measurement of Xe, i.e. the same apparatus recently shown to provide a precise, real-time, every-single-shot, carrier-envelope phase measurement of ultrashort laser pulses. The pulse length is calibrated ...

The very pronounced intensity-dependent enhancements of groups of peaks of high-order above-threshold-ionization spectra of rare-gas atoms are investigated using an improved version of the strong-field approximation, which realistically models the respective atom. Two types of enhancements are found and explained in terms of constructive interference of the contributions of a ...

Results of calculations of the integrated cross section and the energy distribution for ionization of ground-state hydrogen by S1-wave electron impact are presented. The breakup amplitude is expressed as a volume integral that contains an approximate final-state wave function which accounts for postcollision dynamic screening. The error in this wave function is accounted for ...

Two-photon excitation of a single-photon forbidden Auger resonance has been observed and investigated using the intense extreme ultraviolet radiation from the free electron laser in Hamburg. At the wavelength 26.9 nm (46 eV) two photons promoted a 3d core electron to the outer 4d shell. The subsequent Auger decay, as well as several nonlinear above ...

We describe the results of experiments performed in Krypton to observe the effect of an isolated atomic level on harmonic generation at intensities above 10{sup 13} W/cm{sup 2}. We have measured the intensity of harmonics produced as a function of laser intensity and focal conditions as well as recorded the photoelectron energy spectra in complementary experiments. We discuss a simple model fit to ...

The plateaus in laser-assisted recombination and high-order harmonic generation are investigated in the frequency domain. It is found that the probability amplitude of finding an electron with a given energy is given by a generalized Bessel function, which can be represented as a coherent superposition of contributions from a few electronic quantum trajectories. This concept is illustrated by ...

The pulse shape and phase of isolated attosecond extreme ultraviolet (XUV) pulses with a duration of 860 asec have been determined simultaneously by using frequency-resolved optical gating based on two-photon above-threshold ionization with 28-eV photons in He. From the detailed characterization, we succeeded in shaping isolated XUV pulses on an attosecond ...

We report on the direct observation of an attosecond pulse train with a mode-resolved autocorrelation technique. The chirp among the three harmonic fields is specified by analyzing two-photon above-threshold ionization spectra of electrons, resulting in a pulse duration that should be shorter than 450 as, which is, to our knowledge, the first determination ...

. TABLE II: "Raw" formation enthalpies HATi , HVTi (from Eqs. (2-3) at zero pressure), "true" formation. A HATi HA Hls,nv sol Zn 6.405 -0.262 0.218 Cd 7.267 0.24 0.461 Ag 5.412 0.304 0.494 Au 3.882 -0.781 0

We present measurements of the absolute rates for multiphoton ionization of the ground state from atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at a wavelength of 248 nm. A laser crossed atomic beam technique is used. The irradiance was varied from 3{times}10{sup 12} w/cm{sup 2} to 2{times}10{sup 14} w/cm{sup 2} and three above ...

Studies of nonlinear laser-matter interaction have been so far limited to wavelengths from the near ultraviolet to infrared, because of the low brightness of currently available sources outside this range. However nonlinear processes in the VUV/Soft X-ray domain would initiate multiphoton innershell spectroscopy, XUV nonlinear optics and applications of such processes to metrology. The probability ...

Double resonance spectroscopy via theEF ^1?g^+ ,v'EF=6,J' state has been used to probe the H(n=1) + H(n=3) dissociation threshold region with quantum state selectivity and high energy resolution. Above threshold the continuum is detected by ionizing H(n=3) to produce H^+, which is then detected by using a time-of-flight mass ...

A systematic study is reported on the convergence of computed triply differential cross sections for photo-double ionization of helium at 20 and 25 eV above threshold, obtained using the hyperspherical R matrix with semiclassical outgoing waves method. Such a study has become feasible due to an essential improvement in the ...

The generation of highly charged Xe(q+) ions up to q=24 is observed in Xe clusters embedded in helium nanodroplets and exposed to intense femtosecond laser pulses (?=800??nm). Laser intensity resolved measurements show that the high-q ion generation starts at an unexpectedly low threshold intensity of about 10(14)??W/cm2. Above threshold, the Xe ion charge ...

The generation of highly charged Xe{sup q+} ions up to q=24 is observed in Xe clusters embedded in helium nanodroplets and exposed to intense femtosecond laser pulses ({lambda}=800 nm). Laser intensity resolved measurements show that the high-q ion generation starts at an unexpectedly low threshold intensity of about 10{sup 14} W/cm{sup 2}. Above ...

The generation of highly charged Xeq+ ions up to q=24 is observed in Xe clusters embedded in helium nanodroplets and exposed to intense femtosecond laser pulses (?=800nm). Laser intensity resolved measurements show that the high-q ion generation starts at an unexpectedly low threshold intensity of about 1014W/cm2. Above threshold, the Xe ion charge ...

We present the results of a set of quantal and classical calculations designed for simulating the photoelectron spectra observed when atoms are submitted to an intense laser field. We have concentrated the discussion on the range of parameters where conspicuous enhancements are observed in the high-energy part of the above-threshold ionization (ATI) spectra. Our results ...

Numerical results obtained applying the strong-field approximation to atomic and molecular processes in intense laser fields are presented. In particular, the forward-backward asymmetry in high-order above-threshold ionization (HATI) of Ar atoms by a few-cycle laser pulse is considered. It is shown that the resonantlike enhancements observed in the ...

Generalized oscillator strengths and ionization cross sections by fast electron impact are calculated for K, L, and M shells. A nonrelativistic Hartree--Slater program is used to generate the initial states as well as the continuum wave functions. Core edge shapes and their dependence on momentum transfer are computed within this atomic model up to some tens or hundreds of eV ...

We calculate angle-resolved above-threshold ionization spectra for diatomic molecules in linearly polarized laser fields, employing the strong-field approximation. The interference structure resulting from the individual contributions of the different scattering scenarios is discussed in detail, with respect to the dependence on the internuclear distance ...

We have calculated, independently, the {sup 1}S singly differential cross section for the electron-impact ionization of hydrogen at an incident energy of 4.0 eV above threshold using two different methods: time-dependent close coupling and exterior complex scaling. The absolute value of the {sup 1}S cross section for equal energy ...

The threshold law of the titled process, which is of the same form as that for electron-impact ionization of H, can experimentally be contaminated by simultaneous single photodetachment and Rydberg excitation of the residual atom, followed by ionization of the Rydberg atom by (room-temperature) blackbody photons. This gives a signal indistinguishable from ...

The dynamics of highly charged ions in a strong laser field are investigated by solving the two-dimensional time-dependent Dirac equation. Relativistic effects are discussed for the hydrogen-like ions with nuclear charges of Z=4, 24 and 79 by considering the changes in the electron trajectory and coherent emission spectrum with changes in the frequency and intensity of the laser field. With ...

With the help of a suitably chosen momentum-space analysis, we study some of the basic mechanisms governing the physics of the processes occurring when atoms are submitted to intense infrared laser pulses, with peak intensities 10(14) W cm(-2)

A generalization of the analytical theory of above-threshold ionization in the single active electron approximation is developed while taking into account leading non-dipole and relativistic corrections in the starting Hamiltonian. Special interest is placed on the high energy part of the photoelectron spectrum which consists of a plateau and a characteristic cutoff. It is ...

We investigate high-order above-threshold ionization (HATI) of diatomic molecules having different symmetries by an elliptically polarized laser field using the modified molecular strong-field approximation. The yields of high-energy electrons contributing to the plateau region of the photoelectron spectra strongly depend on the employed ellipticity. This ...

Three-photon ionization cross sections from the ground state, and two-photon ionization from the 3 {sup 1}P(3s3p) state have been calculated for Mg in the region between the 3p and 4s ionization thresholds. These processes include an above-threshold ionization process for the last absorbed photon. We have used the ...

The resonantly enhanced multiphoton ionization of atomic hydrogen is studied for the case of four-photon ionization (three-photon resonant). The time-dependent probabilities, the shape of the resonance profile at different intensities, and the nonlinear index are computed for coherent light at frequencies around the resonance (365 nm). The systematic ...

Above-threshold ionization (ATI) ionization by linearly polarized light has been proposed by several authors as a means of driving recombination lasers in the soft x-ray spectral region. The pump radiation generates a cold electron plasma with ions in a single ionization stage, which is an ideal starting condition ...

Above-threshold ionization (ATI) ionization by linearly polarized light has been proposed by several authors as a means of driving recombination lasers in the soft x-ray spectral region. The pump radiation generates a cold electron plasma with ions in a single ionization stage, which is an ideal starting condition ...

This reprint reports a two-color high-resolution energy- and angle-resolved study of the photoelectrons produced in the (1+1) REMPI of NO via rotational levels of the A 2 sigma (+) nu=0 state. Markedly different photoelectron angular distributions arise f...

We use the S-matrix formalism in order to investigate the possible role of incoherent scattering in different processes in a strong laser field. In the cases of above-threshold ionization (ATI) of atoms and above-threshold detachment (ATD) of negative ions, we assume that the ionized (detached) electron may scatter off a target other than its parent ion ...

The mechanism of collision-free multiphoton ionization of rare gases irradiated with ultraviolet radiation at an intensity of up to approx.10/sup 16/ W/cm/sup 2/ at 248 nm and a pulse length of approx.0.5 ps and approx.10/sup 15/ W/cm/sup 2/ at 193 nm and approx.5ps, respectively, has been studied by observing the electron energy spectra and ion charge state threshold ...

By numerical solution of the time-dependent Schroedinger equation, highly accurate electron spectra are calculated for strong-field ionization of a one-dimensional H{sub 2}{sup +} molecular ion at large internuclear distances. Compared to the atomic spectra, we find additional cutoffs at high electron energies. The classical model for ionization ...

Two-color above threshold ionization of helium and xenon has been used to analyze the synchronization between individual pulses of the femtosecond extreme ultraviolet (XUV) free electron laser in Hamburg and an independent intense 120 fs mode-locked Ti:sapphire laser. Characteristic sidebands appear in the photoelectron spectra when ...

According to the quantitative rescattering (QRS) theory, the high-energy Above-threshold-ionization (HATI) electron spectra from a molecule M can be used to extract the differential cross section (DCS) at large scattering angles for e- + M+ collisions. Using mid-infrared (MIR) lasers the rescattering electrons can reach energies from 50 eV to a few hundred eV's where the ...

In this Letter we demonstrate a method for real-time determination of the carrier-envelope phase of each and every single ultrashort laser pulse at kilohertz repetition rates. The technique expands upon the recent work of Wittmann and incorporates a stereographic above-threshold laser-induced ionization measurement and electronics optimized to produce a ...

Polar photodissociation of CF{sub n}Cl{sub 4-n} (n=0-2) has been studied using synchrotron radiation within the energy range 195-217 eV. The first observations of negative photoion fragments from these molecules after core excitation are reported. In addition to observing a number of previously known resonances two additional resonant states, just above the Cl 2p ionization ...

Polar photodissociation of CFnCl4?n(n=0-2) has been studied using synchrotron radiation within the energy range 195-217 eV. The first observations of negative photoion fragments from these molecules after core excitation are reported. In addition to observing a number of previously known resonances two additional resonant states, just above the Cl2p ionization limit, are ...

The occurrence of a fault April 7 caused a short in the stator winding of one of the main generators. Repairs will require at least one month and the total time the generator will be down can be determined only after a further inspection of the damage. In a week or two, after a thorough inspection of the generator and the ignitron system, Bevatron operation will be continued on one generator. ...

Experimental and theoretical results are presented for electron impact ionization of water in the energy regime from near threshold to intermediate energies. Results were taken in symmetric coplanar and non-coplanar geometries, with both equal and non-equal outgoing electron energies. The models approximate the random orientation of the target using a spherical averaging of ...

At high intensities, three-step recollision processes driven by low frequency laser pulses, such as high-order harmonic generation and high-order above-threshold ionization, are normally severely suppressed by the magnetic-field component of the laser field. It is shown that this suppression is not severe, even for ponderomotive energies well above 10 keV, ...

We present a first-principles description for the electron dynamics and multiphoton absorption in crystalline SiO(2) induced by an optical field. We rely upon time-dependent density-functional theory with adiabatic local-density approximation, and a real-space and real-time method is employed to solve the time-dependent Kohn-Sham equation. Computational results show the absorption of photons to be ...

Electron impact ionization has been studied in PH/sub 3/ and in a mixture of PH/sub 3/ and PD/sub 3/ as a function of electron energy up to 180 eV, with a double focusing mass spectrometer. Absolute partial ionization cross sections have been obtained in PH/sub 3/ for the production of the parent ion PH/sup +//sub 3/, for the fragment ions PH/sup +//sub ...

We study above-threshold ionization (ATI) of a one-dimensional model atom in a time-varying external laser field. The time-dependent Schroedinger equation is integrated in space and time using the Crank-Nicholson method, and the photoelectron energy spectrum is then computed by projecting the wave function onto the energy eigenstates of the ...

We study above-threshold ionization (ATI) of a one-dimensional model atom in a time-varying external laser field. The time-dependent Schr�dinger equation is integrated in space and time using the Crank-Nicholson method, and the photoelectron energy spectrum is then computed by projecting the wave function onto the energy eigenstates of the ...

It is found that the mean charge of tungsten ions in a solid tungsten target cleaned from the surface layer of hydrocarbon and oxide compounds and exposed to femtosecond laser radiation with an intensity exceeding 10{sup 16} W/cm{sup 2} attains 22+, while the maximum charge is 29+. The maximum energy of such ions approaches 1 MeV. The corresponding values obtained on a dirty target with the same ...

We address the problem of calculating electromagnetic transition matrix elements between states of a particle in spherically symmetrical potentials with no assumed boundary conditions at finite distance (free-boundary-condition method). For this, the Schroedinger equation is solved in a finite box of radius R and bound and continuum states, appropriately normalized, are numerically represented, ...

We present evidence of a cold multiphoton MALDI process occurring at a Room Temperature Ionic Liquid (RTIL)/metal interface. Our RTIL, 1-Butyl-3-methylimidazolium hexafluorophosphate, remains a stable liquid at room temperatures, even at pressures lower than 10-9 torr. We focus the 2^nd harmonic of a pulsed (2ns pulse length) Nd:YAG laser onto a gold grid coated with RTIL to generate a cold ...

In this final report the author presents a summary of recent research accomplishments. In this grant period (FY90--97), some 36 papers have been published. [See Part 4 for a list of publications]. Significant progress has been made in several areas, both in the development of new theoretical and computational methods, their applications to experimental observations, and in the prediction of some ...

The highly-nonlinear multiphoton phenomenon of high-energy above-threshold ionization (HATI) of an atomic system by an intense laser field is considered theoretically and studied numerically within frame of a new fully quantum-mechanical strong-field approach developed earlier for effective numerical calculation of high-order harmonic generation spectra ...

... WERE DETERMINED SUCH AS SIGNAL DURATION, AE COUNTS (OSCILLATIONS ABOVE THRESHOLD), RISE TIME, AND PEAK AMPLITUDE. ...

The random-phase approximation, developed in the study of the electron gas, was used as a framework for the calculation of atomic excitation energies, oscillator strengths, and photo-ionization cross sections. Numerical results were obtained for the /sup 1/P/sup 0/ states of beryllium, magnesium, calcium, zinc, and strontium. Excitation energies and oscillator ...

We apply a scattering theory of nonperturbative quantum electrodynamics to study the photoelectron angular distributions (PADs) of a hydrogen atom irradiated by linearly polarized laser light. The calculated PADs show main lobes and jetlike structure. Previous experimental studies reveal that in a set of above-threshold-ionization peaks when the absorbed-photon number ...

The mechanisms responsible for matrix-assisted laser desorption/ionization (MALDI) are far from being well understood, particularly where infrared laser irradiation is used to initiate the process. We measured the emission yields and kinetic energy distributions of positive ions emitted from 2,5-dihydroxybenzoic acid loaded with angiotensin II in a standard MALDI preparation ...

A robust nonoptical carrier-envelope phase (CEP) locking feedback loop, which utilizes a measurement of the left-right asymmetry in the above-threshold ionization (ATI) of Xe, is implemented, resulting in a significant improvement over the standard slow-loop f-to-2f technique. This technique utilizes the floating average of a real-time, every-single-shot CEP measurement to ...

We analyze the photoelectron emission spectrum in atomic above-threshold ionization by a linearly polarized short-laser pulse. Direct electrons can be characterized by both intracycle and intercycle interferences. The former results from the coherent superposition of two different electron trajectories released in the same optical cycle, whereas the latter ...

The development of a new class of laser systems: capable of producing intense radiation in the mid-infrared (MIR) regime (photon energies between 0.3 and 0.4 eV), opens the possibility of observing multiphoton processes in a new class of systems with lower ionization potentials than those previously studied. Of particular interest are the alkali metal atoms, which are true ...

A systematic study is reported on the convergence of computed triply differential cross sections for photo-double ionization of helium at 20 and 25 eV above threshold, obtained using the hyperspherical R matrix with semiclassical outgoing waves method. Such a study has become feasible due to an essential improvement in the description ...

The interaction between an atom and a short laser pulse is studied in the case where both photon energies are smaller than the ionization potential and perturbation conditions prevail. Under these conditions, a full numerical solution of the time-dependent Schroedinger equation for a hydrogen atom initially in its ground state shows that secondary peaks show up in the ...

A tunable, high-intensity picosecond dye laser system has been employed with electron energy analysis to investigate the dynamics of (3+1) resonance-enhanced multiphoton ionization of H{sub 2} via different vibrational levels of its B{sub 1}{Sigma}{sub u}{sup +} and C{sup 1}{Pi}{sub u} electronic states. We observe production of molecular ions in various vibrational levels, ...

2,2'-bithiophene in the gas phase was studied by ultraviolet photoelectron spectroscopy (UPS) and two-dimensional Penning ionization electron spectroscopy (2D-PIES) to obtain the information of stereodynamics in Penning ionization and anisotropic interaction around the ionization region. Thiophene and the 2,2'-bithiophene layer on a ...

Plasmas produced in a cold-cathode Penning discharge have been studied for possible use as an active ionizing medium in commercial quadrupole mass/energy analyzers for detection of low-energy neutral beams. Two distinct Penning discharge modes have been examined: (1) high-pressure (HP) mode and (2) high magnetic field (HMF) mode. It is shown that the ...

Plasmas produced in a cold-cathode Penning discharge have been studied for possible use as an active ionizing medium in commercial quadrupole mass/energy analyzers for detection of low-energy neutral beams. Two distinct Penning discharge modes have been examined: (1) high-pressure (HP) mode and (2) high magnetic field (HMF) mode. It is shown that the ...

A brief description is given of the early developments leading to the discovery of some of the basic phenomena that occur during the interaction of intense light fields with atomic systems - such as multiphoton ionization (MPI), above-threshold ionization (ATI), and high harmonic generation (HHG). Also outlined are the related ...

Calculations based on the multiple-scattering method have been performed for the asymmetry parameter (..beta..) as a function of photon energy (from the ionization threshold to 2 Ry above threshold) for the gaseous molecules: N/sub 2/, CO, CO/sub 2/, COS, and CS/sub 2/. For the diatomic molecules N/sub 2/ and CO we have investigated ...

The theoretical developments presented in a preceding companion paper by Wassaf et al. [Phys. Rev. A 67, 053405 (2003)], for simulating photoelectron spectra, are used to address several issues regarding the harmonic generation process. Both above-threshold Ionization (ATI) and high-order harmonic generation are observed when atoms are submitted to a laser ...

We investigate the high-energy above-threshold ionization (HATI) plateau for Xe in a strong laser field at peak intensity of about 0.85�1014W/cm2 with wavelengths of 800, 1250, 1500, and 2000 nm. Numerical simulations are performed using a recently developed quantitative rescattering (QRS) model. According to the QRS model, the two-dimensional (2D) ...

The neutron-induced fission cross section of Np/sup 237/ was measured as a function of neutron energy in the range 0.9 to 8.0 Mev. Measurements above 1.7 Mev were made relative to the fission cross section of U/sup 238/ using 2 pi / sup -/ counting of fission fragmnents from thin fissile deposits placed back to back in a gridded ionization chamber. In the range 0.9 ...

A merged-beams electron-energy-loss technique is described, by which absolute cross sections can be measured for near-threshold electron-impact excitation of multipy charged ions. Results are reported here for absolute total electron-impact excitation cross sections for the O[sup 5+](2[ital s][r arrow]2[ital p]) transition from below threshold to 1.6 eV above ...

Valence ionized states of iron pentacarbonyl Fe(CO)(5) and eta(5)-cyclopentadienyl cobalt dicarbonyl Co(eta(5)-C(5)H(5))(CO)(2) have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable ...

First experiments on atomic photoionization and molecular dissociation have been performed by taking advantage of the unprecedented characteristics of the free electron laser in Hamburg (FLASH) combined with a separate near-infrared (NIR) femtosecond laser. In a series of two-colour experiments, the photoionization of rare gases in the presence of a strong NIR dressing field as well as the ...

An electron imaging technique has been used to study the full angular distribution of valence photoelectrons produced from enantiomerically pure molecular beams of camphor when these are photoionized with circularly polarized light. In addition to the familiar ? parameter, this provides a new chiral term, taking the form of an additional cosine function in the angular distribution which ...

Above threshold ionization (ATI) spectra of small metal clusters (e.g., Na{sub 4} and Na{sub 4}{sup +}) are calculated numerically using a spherical jellium model and time-dependent density functional theory for two-color (1064 and 532 nm) ultrashort (25 fs) laser pulses as a function of phase difference between the two fields. ATI ...

Above threshold ionization (ATI) spectra of small metal clusters (e.g., Na4 and Na+4 ) are calculated numerically using a spherical jellium model and time-dependent density functional theory for two-color (1064 and 532 nm ) ultrashort ( 25 fs ) laser pulses as a function of phase difference between the two fields. ATI spectra and ...

An equation relating the photocurrent just above threshold to the binding energy of the solvated electron is compared to experimental data. (AIP)

Figure 9b. Laser Energy Transmission Through the Focal. Volume as a Function of Time for Power Density. Input Well Above Threshold in 3.0 Atmospheres ...

Series switching diodes triggered on by passing above threshold voltage. High-voltage switch made by

A storage-ring free-electron laser oscillator has been operated above threshold at a visible wavelength lambdaapprox. =6500 A.

... Little tunny - Gulf of Mexico SAFMC / GMFMC No Undefined Unknown

o Manufacturing Defect such as improper heat treat o Stress Corrosion cracking due to prolonged exposure to ammonium hydroxide and stresses above threshold ...

The cascaded Auger decay following ionization or excitation with 94 eV soft-X-ray pulses from the 3 d subshell in krypton has been energy-and-time-resolved for the first time. The decay time of the 4 s -14 p -2 nl ? 4 p -3 + e and/or 4 s -14 p -1 nl ? 4 p -2 + e transition is measured to be 74 � 20 fs. Furthermore, our data shows that the electrons with a kinetic energy ...

Positive-mode atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS(n)) was tested for the differentiation of regioisomeric aromatic ketocarboxylic acids. Each analyte forms exclusively an abundant protonated molecule upon ionization via positive-mode APCI in a commercial linear quadrupole ion trap (LQIT) mass spectrometer. ...

Collision energy dependence of partial ionization cross sections (CEDPICS) of p-benzoquinone with He*(2 3S) metastable atoms indicates that interaction potentials between p-benzoquinone and He*(2 3S) are highly anisotropic in the studied collision energy range (100-250 meV). Attractive interactions were found around the C=O groups for in-plane and out-of-plane directions, ...

When an atom or molecule is exposed to a short intense laser pulse, electrons that were removed at an earlier time may be driven back by the oscillating electric field of the laser to recollide with the parent ion, to incur processes like high-order harmonic generation (HHG), high-energy above-threshold ionization (HATI) and nonsequential double ...

Nonlinear responses to an optical field are universal in nature but have been difficult to observe in the extreme ultraviolet (XUV) and soft X-ray regions owing to a lack of coherent intense light sources. High harmonic generation is a well-known nonlinear optical phenomenon and is now drawing much attention in attosecond pulse generation. For the application of high harmonics to nonlinear optics ...

We have studied the dissociative ionization behavior of Na2 molecules using two-color, three photon optical-optical double resonance enhanced excitation via the A(1)Sigma(u)(+) and the 2(1)Pi(g) states. Excess energy ranges from about 150 to about 1500 cm(-1) above threshold for dissociative ionization into ...

The dissociative photoionization processes of H2 and D2 in an intense, short-pulsed soft x-ray field (? = 29.6 nm, 3 � 1012 W cm-2, 15 fs) generated as the 27th high-order harmonic of a Ti:sapphire laser is investigated for the first time by time-of-flight mass spectrometry. The ejected H+ fragment ions from H2 are distributed in the kinetic energy range of 3-20 eV peaked at 10.0 eV, and the ...

We present an application of the artificial-channel method to the calculation of multiphoton ionization rates under continuous-wave illumination conditions. We use the method to treat above-threshold ionization (ATI) of hydrogen in three dimensions with linearly and circularly polarized light at field intensities ranging from 10[sup 9] ...

A theoretical analysis of laser-driven collisional ejection of inner-shell electrons is presented to explain the previously observed anomalous kilovolt L-shell x-ray emission spectra from atomic Xe cluster targets excited by intense sub-picosecond 248nrn ultraviolet radiation. For incident ponderomotively-driven electrons photoionized by strong above ...

Absolute ionization cross sections have been measured for the processes N$sub 2$+e$Yields$N$sub 2$$sup +$+2e, N$sub 2$+e$Yields$N$sub 2$$sup ++$+3e, O$sub 2$+e$Yields$O$sub 2$$sup +$+2e, and O$sub 2$+e$Yields$O$sub 2$$sup ++$+3e as a function of electron energy up to 170 eV in a crossed molecule--electron beam apparatus. The ionization cross ...

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An injection laser is automatically stabilized so that the laser operates above threshold when the laser current is modulated. The invention makes use of the fact that the laser junction voltage saturates at currents above the threshold. A signal which modulates the laser current and causes the laser current to fall below the threshold level therefore ...

The authors study the longitudinal mode discrimination above threshold in both distributed feedback lasers with one external reflector and those with phase-shifted grating structures. By numerically solving a pair of coupled mode equations, they show that when these types of lasers have nonsaturable index coupling, they lose their mode discrimination at ...

Total ionization and attachment cross sections have been measured in C/sub 3/F/sub 8/ at 330 K using an electron beam and a total ion collection technique, calibrated by similar measurements on N/sub 2/O and Xe. Our total ionization cross section is similar in general shape to a previous measurement of this type, but with typically half the magnitude. The ...

Gaseous C{sub 60} has been studied by photoionization mass spectrometry between the ionization threshold and 40.8 eV. An adiabatic threshold of 7.57{plus minus}0.01 eV is observed, which may be slightly low due to hot bands. The energy derivative of the photoion yield curve is in rough agreement with the He I photoelectron spectrum on the positions of some peaks, but others ...

The photoionization efficiency (PIE) spectra for cold iron clusters (Fe{sub 6}--Fe{sub 90}) and cobalt clusters (Co{sub 3}, Co{sub 7}--Co{sub 92}) have been measured using a tunable ultraviolet laser combined with time-of-flight mass spectrometry. Vertical ionization potentials (IPs) assigned from the observed photoionization thresholds decrease rapidly but nonmonotonically ...

Over the last few years, electron beam ionization has been shown to be a viable generator of high density plasmas with numerous applications in materials modification. To better understand these plasmas, we have fielded electron beam diagnostics to more clearly understand the propagation of the beam as it travels through the background gas and creates the plasma. These ...