Photoelectron Energy Spectra Research Articles

Photoelectron flux variations observed from the FAST satellite

This paper examines high resolution (Δ E/ E = 0.15) photoelectron energy spectra from 10 eV to 1 keV, created by solar irradiances between 1.2 and 120 nm. The observations were made from the FAST satellite at ∼3000 km, equatorward of the auroral oval for the July–August, 2002 solar rotation. These data are compared with the solar irradiance observed by the Solar EUV Experiment (SEE) on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and fluxes calculated using the Field Line Interhemispheric Plasma (FLIP) code. The 41 eV photoelectron flux, which corresponds to solar EUV fluxes near 20 nm, shows a clear solar rotation variation in very good agreement with the EUV flux measurements. This offers the possibility that the 41 eV photoelectron flux could be used as a check on measured solar EUV fluxes near 20 nm. Because of unexpected noise, the solar rotation signal is not evident in the integral photoelectron flux between 156 and 1000 eV corresponding to EUV wavelengths between 0.1 and 7 nm measured by the SEE instrument. Examination of daily averaged photoelectron fluxes at energies between 25 and 500 eV show significant changes in the photoelectron spectra in response X and M class flares. The intensity of photoelectrons produced in this energy region is primarily due to two very narrow EUV wavelength regions at 2.3 and 3 nm driving Auger photoionization in O at 500 eV and N 2 at ∼360 eV. Comparison of calculated and daily averaged electron fluxes shows that the HEUVAC model solar spectrum used in the FLIP code does not reproduce the observed variations in photoelectron intensity. In principle, the 21 discrete photoelectron energy channels could be used to improve the reliability of the solar EUV fluxes at 2.3 and 3 nm inferred from broad band observations. In practice, orbital biases in the way the data were accumulated and/or noise signals arising from natural and anthropogenic longitudinally restricted sources of ionization complicate the application of this technique.

Interference effects in photodetachment ofF−in a strong circularly polarized laser pulse

A numerical simulation of photodetachment of F{sup -} by a circularly polarized laser pulse has been accomplished by using a Keldysh-type approach. The numerical results are in agreement with measurements of photoelectron energy spectra recently reported in the literature. The features exhibited by the spectra are traced back to quantum interference effects, in the same spirit as in a double-slit experiment in the time doma0008.

Spectral and partial-wave decomposition of time-dependent wave functions on a grid: Photoelectron spectra of H andH2+in electromagnetic fields

We present a method for spectral (bound and continuum) and partial-wave analysis of a three-dimensional time-dependent wave function, defined on a grid, without projecting onto the field-free eigenstates of the system. The method consists of propagating the time-dependent Schr\"odinger equation to obtain its autocorrelation function $C(t)=⟨\ensuremath{\psi}(\mathbf{r},T)\ensuremath{\mid}\ensuremath{\psi}(\mathbf{r},T+t)⟩$ after the end of the interaction, at time $T$, of the system with an external time-dependent field. The Fourier spectrum of this correlation function is directly related to the expansion coefficients of the wave function on the field-free bound and continuum energy eigenstates of the system. By expanding on a spherical harmonics basis we show how to calculate the contribution of the various partial waves to the total photoelectron energy spectrum.

Above-threshold ionization by chirped laser pulses

We theoretically investigate above-threshold ionization by chirped laser pulses. By comparing the photoelectron energy spectra and the photoelectron angular distributions of Na for the laser pulses with different chirp rates but with the identical spectral profile, we find that the ionization processes have a clear dependence on the chirp rate. Further calculations without excited bound states during the time propagation of the wave function reveal practically no chirp dependence, which is clear evidence that the origin of the chirp dependence in above-threshold ionization is the excited bound states.

Coulomb effects in photoionization of H atoms irradiated by intense laser fields

We theoretically study the Coulomb effects on the photoionization processes of the H atom irradiated by the intense laser fields with circular and linear polarizations. For this purpose we represent the final continuum state by the Coulomb-Volkov state. Total ionization rates, photoelectron energy spectra, and angular distribution of photoelectrons are calculated and compared with those obtained using the Volkov state. We find that how much the Coulomb field influences the ionization dynamics depends on the momentum of photoelectrons, among which the photoelectron angular distributions in the linearly polarized laser field represent the most striking difference.

Features of the energy spectra of photoelectrons at the atomic ionization in a two-color laser field of first and third harmonics

Classical analysis and quantum-mechanical studies of the energy spectra of photoelectrons have been carried out for above-threshold ionization of atoms in a two-color laser field of the first and third (n = 3) harmonics. Numerical computations show that the boundary of direct ionization plateau corresponds to the electron energy E ≈ 3.56 \(U_{p_1 } \), while the boundary of rescattering plateau corresponds to the electron energy E ≈ 16.62 \(U_{p_1 } \) for the two-color field of fundamental frequency and its third harmonic with equal intensities, which is in accordance with the results of classical analysis. The results of classical analysis of the ionization processes in the field of first and nth harmonics of equal intensities show that the length of the direct ionization plateau and the length of the high-energy rescattering plateau decrease with increasing n. The results of numerical analysis of the ionization processes in the field of first and third (n = 3) harmonics correspond to the results of classical analysis carried out by the authors.

Population transfer of the Na 2 molecule via continuum state

The population transfer between the different electronic states through the ionization continuum state is studied for the Na 2 molecule using the quantum wave packet method. The population evolutions of the initial A 1 Σ u + state, the target 2 1 Π g state and the ionization continuum 2 Σ g + state with time are discussed in detail. The time-dependent photoelectron energy spectra are calculated. It is demonstrated that the population can be efficiently transferred from the A 1 Σ u + state to the 2 1 Π g state via the 2 Σ g + state by properly choosing the intensities and the detunings of the pump and Stokes pulses. The effects of one-photon detuning and molecular rotation and alignment on the population transfer are also discussed.

Large solid-angle analyzer applied to angle-resolved ultraviolet photoelectron spectroscopy

We have applied a large acceptance solid-angle energy analyzer to measure angle-resolved energy spectra of photoelectrons excited by ultraviolet light. The observed photoemission patterns as a function of a binding energy provides the energy dispersion curves of highly oriented pyrolytic graphite. The measured dispersion curves of the σ and π bands agree with both the reported and theoretical ones based on ab initio calculations. The energy resolution of the analyzer estimated in this experiment agrees with the reported value measured by EELS experiment. The comparison of properties of three different analyzers clarifies that the simultaneous realization of the short measurement time and high energy resolution is the most advantageous feature of this analyzer.

Laser-phase determination methods and transfer equations for direct temporal structure measurements of atto- and femtosecond XUV pulses

In this paper the laser-phase determination methods and transfer equations are presented to directly reconstruct the detailed temporal structures of ultra-short extreme ultraviolet (xuv) pulses from the measured photoelectron energy spectra (PES). Each transfer equation includes one of PID (proportional-integral-differential) terms of PES. The intensity and instantaneous frequency of attosecond xuv can be retrieved from the integral term of PES. The intensity profiles of narrow bandwidth atto- and femtosecond xuvs can be rebuilt from the proportional and differential terms of PES respectively. The methods and equations may be used to improve time resolutions in measuring ultrashort pulses.

Study on the High Efficiency Antioxidant of Polyoxymethylene

This article reports on the properties and uses of antioxidant F/B, a type of high efficiency antioxidant for polyoxymethylene (POM), consisting of the hindered phenolic main antioxidant, the secondary thermostabilizer phosphite ester, and lactone compound. Our experimental studies focused on the thermostabilization effect of antioxidant F/B on POM, which was measured by isothermal weight loss analysis at 220°C, isothermal weight loss rate analysis at 222°C, balance torque analysis, nonisothermal gravity analysis (TGA), oxidation induction time (OIT) analysis, and multiple processing and long-term aging analysis as compared to the commonly used antioxidant Irganox245 of POM. The results showed that the thermal stability of POM can be improved remarkably by using antioxidant F/B. The aging mechanism of POM under heat and oxygen was studied by the measurements of polarized light microscopy (PLM), differential scanning calorimetry (DSC), and X-ray photoelectron energy spectrum (XPS), which showed very slight changes of spherulites dimension, crystallinity, and the surface atom concentration after 15 days of aging at 140°C. Furthermore, the small amount of degradation of POM only occurred in the amorphous region of POM. These experiments demonstrated that lower amounts of antioxidant F/B can reach the same level of thermal stabilization of POM as is achieved with higher amounts of Irganox245, and can replace Irganox245 for use in the production of POM, which can further improve the thermal stabilization and reduce the production cost of POM.

Above-threshold ionization of Mg by linearly and circularly polarized laser fields: Origin of the subpeaks in the photoelectron energy spectra

We theoretically investigate above-threshold ionization of Mg by linearly and circularly polarized fs laser pulses. We find that the above-threshold ionization peaks are accompanied by small subpeaks for both linearly and circularly polarized pulses. We interpret the physical origin of the subpeaks as above-threshold ionization from the low-lying bound states which are far off-resonantly excited by the spectral wing of the pulse. This interpretation is confirmed by our comparative numerical studies. Furthermore, we provide a clear explanation of why this kind of subpeak in the photoelectron energy spectra has not been reported for smaller photon energies with Mg and other commonly used atoms such as H and rare gas atoms.

Photoionization of NaK molecule with a double-well potential in femtosecond pump–probe pulse laser fields

The method of time-dependent quantum wave packet dynamics is used to calculate the femtosecond pump–probe photoelectron spectra and study the wave packet dynamic processes of the double-minimum potential state 61Σ+ of NaK in intense laser fields. The evolutions of the wave packet and the photoelectron energy spectra with time and internuclear distance are described in detail. The wave packet dynamic information of the 61Σ+ state can be extracted from the photoelectron energy spectra.

Temporal Young’s interference experiment by attosecond double and triple soft-x-ray pulses

We study a temporal version of Young's interference experiment by attosecond soft-x-ray pulses. The photoelectron energy spectra by attosecond double pulses exhibit an interference pattern, since we have no information on which pulse has generated the electron. We can re-establish the ``which-way'' information and control the interference visibility by changing the electron's momentum with phase-stabilized laser pulses, by an amount depending on the time of ionization. Moreover, if we use a triple pulse, we can realize a situation where the electron passes through a single and a double slit simultaneously to the same direction and is observed by the same detector.

Numerical interpretation of high-altitude photoelectron observations

The Electron Spectrometer (ELS) instrument of the ASPERA-3 package on the Mars Express satellite has recorded photoelectron energy spectra up to apoapsis ( ∼ 10 , 000 km altitude). The characteristic photoelectron shape of the spectrum is sometimes seen well above the ionosphere in the evening sector across a wide range of near-equatorial latitudes. Two numerical models are used to analyze the characteristics of these high-altitude photoelectrons. The first is a global, multi-species MHD code that produces a 3-D representation of the magnetic field and bulk plasma parameters around Mars. It is used here to examine the possibility of magnetic connectivity between the high-altitude flanks of the martian ionosheath and the subsolar ionosphere. It is shown that some field lines in this region are draped interplanetary magnetic lines while others are open field lines (connected to both the IMF and the crustal magnetic field sources). The second model is a kinetic electron transport model that calculates the electron velocity space distribution along a selected, non-uniform, magnetic field line. It is used here to simulate the high-altitude ELS measurements. It is shown that the photoelectrons are essentially confined to the source cone, as governed by magnetic field inhomogeneity along the field line. Reasonable agreement is shown between the data and the model results, and a method is demonstrated for inferring properties of the local and photoelectron source region magnetic field from the ELS measurements. Specifically, the number of sectors in which photoelectrons are measured is a function of the magnetic field intensity ratio and the field's angle with respect to the detector plane. In addition, the sector of the photoelectron flux peak is a function of the magnetic field azimuthal angle in the detector plane.

Laser-Induced Continuum Structure of NO Molecules in Two-ColourFemtosecond Pulsed Laser Fields

The method of quantum wave packet dynamics is used to study themultiphoton ionization of NO molecules via a two-photon Ramancoupling and a laser-induced continuum structure (LICS) state intwo-colour strong femtosecond pulsed laser fields. Time-andenergy-resolved photoelectron energy spectra are calculated fordescribing three photoionization channels. The population transfersthrough the LICS and the Raman coupling passages are discussed.

Laser phase determination and transfer equation to directly measure the temporal structure of narrow bandwidth attosecond XUV pulse

A laser phase determination method and a transfer equation which makes use of the proportional term of the measured photoelectron energy spectrum are presented to directly measure the detailed temporal structure of a narrow bandwidth attosecond XUV pulse. The method is based on the spectrum measurement of electrons generated by XUV photo-ionization interacting with a femtosecond laser field. The results of the study suggest that the measurement should be taken at 0° or 180° with respect to the linear laser polarization. The method has a temporal measurement range of about half a laser oscillation period. The temporal resolution also depends on the jitter and control precision of the laser and XUV pulses.

Photoionization of NO molecule in two-color femtosecond pulse laser fields

A theoretical approach used for studying the multiphoton ionization of NO molecule in two-color strong femtosecond pulse laser fields is proposed. Time- and energy-resolved photoelectron energy spectra are calculated for describing the photionization process. The NO molecule is first excited to the D 2Σ + Rydberg state. The pump and probe pulses then couple the D 2Σ + with M 2Σ + states via a two-photon Raman coupling and a laser-induced continuum structure state. Three channels from the D 2Σ + and M 2Σ + states to ionization state are described. The population transfers through the continuum state and the Raman coupling passage are also calculated.

Direct measurement of the temporal structure of narrow bandwidth femtosecond XUV using ultra-short laser via differential photoelectron energy spectrum

A method is introduced to directly measure the temporal structure of femtosecond XUV which has a narrow bandwidth using sub_picosecond duration laser. Calculati on shows that such a temporal structure can be reconstructed from the differenti al photoelectron energy spectrum excited by XUV or x ray, modulated by a laser field and measured at 90° or 0° with respect to the linear laser polarizatio n. The effectiveness and nonlinearity of the method are investigated. Energy res olution and bin(s) are important parameters for measurement and calculation. The method has a broad temporal measurement range and can be used for researches of dynamic processes associated with atomic motions.

A new method for directly measuring frequency and intensity temporal profiles of attosecond XUV pulse simultaneously and completely

A new method of phase determination is presented to measure the frequency and intensity temporal profiles of attosecond XUV pulses directly, simultaneously and completely. Using a cross correlation between femtosecond laser and attosecond X UV, such profiles can be reconstructed from photoelectron energy spectra measure d with two different laser intensities at 0° and 180° with respect to the line ar laser polarization. The method has a temporal measurement range from a quarte r to about half of laser oscillation period. The temporal resolution depends on the jitter and control precision of the laser and XUV pulses. The method can be used for ultra_fast measurement on attosecond time scale.

Zero electron kinetic energy photoelectron and threshold photoionization spectroscopy of M-X(CH3)3 (M = Ga, In; X = P, As)

This paper presents pulsed-field ionization, zero electron kinetic energy (ZEKE) photoelectron and threshold photoionization spectra of M-X(CH3)3 (M = Ga, In; X = P, As). The ZEKE spectra exhibit well-resolved vibrational structures. A comparison with B3LYP calculations shows that the spectrum of In-P(CH3)3 arises from the 1A1 ← 2E transition and the spectra of Ga-P(CH3)3 and Ga-As(CH3)3 arise from transitions of a Jahn–Teller distorted doublet state to the 1A1 state. The intensities of the 1A1–2E transition in the indium species are described with the Franck–Condon approximation, while the transitions in the gallium complexes are more complicated due to the dynamic Jahn–Teller effect. The adiabatic ionization potentials of Ga-P(CH3)3, In-P(CH3)3, and Ga-As(CH3)3 are 39 635, 38 930, and 40 322 cm–1, respectively, and the ionization threshold of In-As(CH3)3 is ~39 550 cm–1. The metal–ligand stretching frequencies are 143, 116, and 125 cm–1 for Ga+-P, In+-P, and Ga+-As, respectively, and 96 cm–1 for In-P. The intermolecular bending frequencies are 71, 65, and 42 cm–1 for Ga+-P-C, In+-P-C, and Ga+-As-C, respectively, and 47 cm–1 for In-P-C. In addition, ligand-based vibrational frequencies are determined for the CH3 wag, PC3 and AsC3 umbrella, and P-C stretching vibrations. Key words: ZEKE photoelectron, photoionization, DFT, gallium–phosphine, gallium–arsine, indium–phosphine, indium–arsine.