The Experts below are selected from a list of 351 Experts worldwide ranked by ideXlab platform
Shihi Chu - One of the best experts on this subject based on the ideXlab platform.
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Generalized Floquet Formulation of Time-Dependent Density Functional Theory for Many-Electron Systems in Intense Laser Fields
2016Co-Authors: Dmitry A. Telnov*f, Shihi ChuAbstract:Abstract. We present some recent new developments of the generalized Floquet formulation of time-dependent density functional theory (TDDFT) for nonpertur-bative treatment of Multiphoton processes of many-electron quantum systems in in-tense monochromatic or multi-color laser fields. It is shown that the periodically or quasi-periodically (polychromatic) time-dependent Kohn-Sham equations can be ex-actly transformed into an equivalent time-independent Floquet Hamiltonian matrix eigenvalue problems. A procedure is presented for the treatment of bound-bound transitions. For the bound-free transitions, such as Multiphoton Ionization (MPI) or Multiphoton dissociation processes, we introduce the notion of "complex density" and present a non-Hermitian Floquet formalism for the treatment of complex quasi-energies of individual spin-orbitals and total many-electron systems. The procedure is demonstrated by a case study of photoIonization of He atoms in the photon energy range of 25 to 50 eV. Good agreement with recent experimental data is obtained. We also perform some MPI study of He and Be atoms in intense monochromatic and two-color laser fields
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theoretical study of orientation dependent Multiphoton Ionization of polyatomic molecules in intense ultrashort laser fields a new time dependent voronoi cell finite difference method
Chemical Physics, 2009Co-Authors: Sangkil Son, Shihi ChuAbstract:We present a new grid-based time-dependent method to investigate Multiphoton Ionization (MPI) of polyatomic molecules in intense ultrashort laser fields. The electronic structure of polyatomic molecules is treated by the density-functional theory (DFT) with proper long-range potential and the Kohn–Sham equation is accurately solved by means of the Voronoi-cell finite difference method on non-uniform and highly adaptive molecular grids utilizing geometrical flexibility of the Voronoi diagram. This method is generalized to the time-dependent problems with the split-operator time-propagation technique in the energy representation, allowing accurate and efficient non-perturbative treatment of attosecond electronic dynamics in strong fields. The new procedure is applied to the study of MPI of N2 and H2O molecules in intense linearly-polarized and ultrashort laser fields with arbitrary field–molecule orientation. Our results demonstrate that the orientation dependence of MPI is determined not just by the highestoccupied molecular orbital (HOMO) but also by the symmetries and dynamics of other contributing molecular orbitals. In particular, the inner orbitals can show dominant contributions to the Ionization processes when the molecule is aligned in some specific directions with respect to the field polarization. This feature suggests a new way to selectively probe individual orbitals in strong-field electronic dynamics.
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effects of multiple electronic shells on strong field Multiphoton Ionization and high order harmonic generation of diatomic molecules with arbitrary orientation an all electron time dependent density functional approach
Physical Review A, 2009Co-Authors: Dmitry A Telnov, Shihi ChuAbstract:We present a time-dependent density-functional theory approach with proper long-range potential for an ab initio study of the effect of correlated multielectron responses on the Multiphoton Ionization (MPI) and high-order harmonic generation (HHG) of diatomic molecules ${\text{N}}_{2}$ and ${\text{F}}_{2}$ in intense short laser pulse fields with arbitrary molecular orientation. We show that the contributions of inner molecular orbitals to the total MPI probability can be sufficiently large or even dominant over the highest-occupied molecular orbital, depending on detailed electronic structure and symmetry, laser field intensity, and orientation angle. The multielectron effects in HHG are also very important. They are responsible for enhanced HHG at some orientations of the molecular axis. Even strongly bound electrons may have a significant influence on the HHG process.
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multielectron effects on the orientation dependence and photoelectron angular distribution of Multiphoton Ionization of co 2 in strong laser fields
Physical Review A, 2009Co-Authors: Sangkil Son, Shihi ChuAbstract:We perform an ab initio study of Multiphoton Ionization (MPI) of carbon dioxide in intense linearly polarized laser pulses with arbitrary molecular orientation by means of a time-dependent density-functional theory (TDDFT) with proper long-range potential. We develop a time-dependent Voronoi-cell finite difference method with highly adaptive molecular grids for accurate solution of the TDDFT equations. Our results demonstrate that the orientation dependence of MPI is determined by multiple orbital contributions and that the electron correlation effects are significant. The maximum peak of MPI is predicted to be at $40\ifmmode^\circ\else\textdegree\fi{}$ in good agreement with recent experimental data. Photoelectron angular distribution reveals the delicate relation between the orientation dependence and the molecular orbital symmetry.
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ab initio study of the orientation effects in Multiphoton Ionization and high order harmonic generation from the ground and excited electronic states of h2
Physical Review A, 2007Co-Authors: Dmitry A Telnov, Shihi ChuAbstract:We present an ab initio three-dimensional (3D) calculation of Multiphoton Ionization (MPI) and high-order harmonic generation (HHG) of the hydrogen molecular ions subject to intense linearly polarized laser pulses. The orientation of the molecular axis with respect to the polarization of the laser field can be arbitrary. The numerical procedure involves the extension of the generalized pseudospectral (GPS) method for nonuniform spatial discretization of the Hamiltonian and wave functions and time propagation using the split-operator technique in the energy representation. The calculations were performed for the ground and two first excited electronic states of $\mathrm{H}_{2}{}^{+}$ at the internuclear separation $R=2.0\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ The laser pulse has a sine-squared envelope and contains 20 optical cycles with the wavelength $800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The dependence of MPI and HHG on the orientation angle is analyzed. We show that orientation effects are strongly affected by the symmetry of the wave function and the corresponding distribution of the electron density. While the anisotropy of MPI and HHG is rather weak for the $1{\ensuremath{\sigma}}_{g}$ state, both processes are suppressed at the orientation angle 90\ifmmode^\circ\else\textdegree\fi{} for the $1{\ensuremath{\sigma}}_{u}$ state and at the angle 0\ifmmode^\circ\else\textdegree\fi{} for the $1{\ensuremath{\pi}}_{u}$ state. We discuss the Multiphoton resonance and two-center interference effects in the HHG spectra which can lead both to enhancement and suppression of the harmonic generation.
Wei Kong - One of the best experts on this subject based on the ideXlab platform.
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electron impact Ionization and Multiphoton Ionization of doped superfluid helium droplets a comparison
Journal of Chemical Physics, 2016Co-Authors: Yunteng He, Jie Zhang, Wei KongAbstract:We compare characteristics of electron impact Ionization (EI) and Multiphoton Ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two Ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different Ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the Ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and Ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping whi...
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electron impact Ionization and Multiphoton Ionization of doped superfluid helium droplets a comparison
Journal of Chemical Physics, 2016Co-Authors: Jie Zhang, Wei KongAbstract:We compare characteristics of electron impact Ionization (EI) and Multiphoton Ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two Ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different Ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the Ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and Ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters.
Jie Zhang - One of the best experts on this subject based on the ideXlab platform.
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electron impact Ionization and Multiphoton Ionization of doped superfluid helium droplets a comparison
Journal of Chemical Physics, 2016Co-Authors: Yunteng He, Jie Zhang, Wei KongAbstract:We compare characteristics of electron impact Ionization (EI) and Multiphoton Ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two Ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different Ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the Ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and Ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping whi...
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electron impact Ionization and Multiphoton Ionization of doped superfluid helium droplets a comparison
Journal of Chemical Physics, 2016Co-Authors: Jie Zhang, Wei KongAbstract:We compare characteristics of electron impact Ionization (EI) and Multiphoton Ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two Ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different Ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the Ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and Ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters.
Dmitry A Telnov - One of the best experts on this subject based on the ideXlab platform.
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effects of multiple electronic shells on strong field Multiphoton Ionization and high order harmonic generation of diatomic molecules with arbitrary orientation an all electron time dependent density functional approach
Physical Review A, 2009Co-Authors: Dmitry A Telnov, Shihi ChuAbstract:We present a time-dependent density-functional theory approach with proper long-range potential for an ab initio study of the effect of correlated multielectron responses on the Multiphoton Ionization (MPI) and high-order harmonic generation (HHG) of diatomic molecules ${\text{N}}_{2}$ and ${\text{F}}_{2}$ in intense short laser pulse fields with arbitrary molecular orientation. We show that the contributions of inner molecular orbitals to the total MPI probability can be sufficiently large or even dominant over the highest-occupied molecular orbital, depending on detailed electronic structure and symmetry, laser field intensity, and orientation angle. The multielectron effects in HHG are also very important. They are responsible for enhanced HHG at some orientations of the molecular axis. Even strongly bound electrons may have a significant influence on the HHG process.
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ab initio study of the orientation effects in Multiphoton Ionization and high order harmonic generation from the ground and excited electronic states of h2
Physical Review A, 2007Co-Authors: Dmitry A Telnov, Shihi ChuAbstract:We present an ab initio three-dimensional (3D) calculation of Multiphoton Ionization (MPI) and high-order harmonic generation (HHG) of the hydrogen molecular ions subject to intense linearly polarized laser pulses. The orientation of the molecular axis with respect to the polarization of the laser field can be arbitrary. The numerical procedure involves the extension of the generalized pseudospectral (GPS) method for nonuniform spatial discretization of the Hamiltonian and wave functions and time propagation using the split-operator technique in the energy representation. The calculations were performed for the ground and two first excited electronic states of $\mathrm{H}_{2}{}^{+}$ at the internuclear separation $R=2.0\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ The laser pulse has a sine-squared envelope and contains 20 optical cycles with the wavelength $800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The dependence of MPI and HHG on the orientation angle is analyzed. We show that orientation effects are strongly affected by the symmetry of the wave function and the corresponding distribution of the electron density. While the anisotropy of MPI and HHG is rather weak for the $1{\ensuremath{\sigma}}_{g}$ state, both processes are suppressed at the orientation angle 90\ifmmode^\circ\else\textdegree\fi{} for the $1{\ensuremath{\sigma}}_{u}$ state and at the angle 0\ifmmode^\circ\else\textdegree\fi{} for the $1{\ensuremath{\pi}}_{u}$ state. We discuss the Multiphoton resonance and two-center interference effects in the HHG spectra which can lead both to enhancement and suppression of the harmonic generation.
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beyond the floquet theorem generalized floquet formalisms and quasienergy methods for atomic and molecular Multiphoton processes in intense laser fields
Physics Reports, 2004Co-Authors: Shihi Chu, Dmitry A TelnovAbstract:The advancement of high-power and short-pulse laser technology in the past two decades has generated considerable interest in the study of Multiphoton and very high-order nonlinear optical processes of atomic and molecular systems in intense and superintense laser fields, leading to the discovery of a host of novel strong-field phenomena which cannot be understood by the conventional perturbation theory. The Floquet theorem and the time-independent Floquet Hamiltonian method are powerful theoretical framework for the study of bound–bound Multiphoton transitions driven by periodically time-dependent fields. However, there are a number of significant strong-field processes cannot be directly treated by the conventional Floquet methods. In this review article, we discuss several recent developments of generalized Floquet theorems, formalisms, and quasienergy methods, beyond the conventional Floquet theorem, for accurate nonperturbative treatment of a broad range of strong-field atomic and molecular processes and phenomena of current interests. Topics covered include (a) artificial intelligence (AI)—most-probable-path approach (MPPA) for effective treatment of ultralarge Floquet matrix problem; (b) non-Hermitian Floquet formalisms and complex quasienergy methods for nonperturbative treatment of bound–free and free–free processes such as Multiphoton Ionization (MPI) and above-threshold Ionization (ATI) of atoms and molecules, Multiphoton dissociation (MPD) and above-threshold dissociation (ATD) of molecules, chemical bond softening and hardening, charge-resonance enhanced Ionization (CREI) of molecular ions, and multiple high-order harmonic generation (HHG), etc.; (c) many-mode Floquet theorem (MMFT) for exact treatment of Multiphoton processes in multi-color laser fields with nonperiodic time-dependent Hamiltonian; (d) Floquet–Liouville supermatrix (FLSM) formalism for exact nonperturbative treatment of time-dependent Liouville equation (allowing for relaxations and dephasing mechanisms) and high-order nonlinear optical processes (such as intensity-dependent nonlinear optical susceptibilities and Multiphoton resonance fluorescence, etc.); (e) generalized Floquet approaches for the treatment of nonadiabatic and complex geometric phases involving Multiphoton transitions; (f) generalized Floquet techniques for the treatment of Multiphoton processes in intense laser pulse fields with nonperiodic time-dependent Hamiltonians; (g) Floquet formulations of time-dependent density functional theory (DFT) and time-dependent current DFT for nonperturbative treatment of Multiphoton processes of many-electron quantum systems in periodic or polychromatic (quasiperiodic) laser fields. For each generalized Floquet approach, we present also the corresponding development of new computational techniques for facilitating the study of strong-field processes and phenomena. The advancement of these generalized Floquet formalisms and quasienergy methods provides powerful new theoretical frameworks and accurate computational methods for nonperturbative and ab initio treatment of a wide range of interesting and challenging laser-induced chemical and physical processes and insightful exploration of strong-field atomic and molecular physics.
Totaro Imasaka - One of the best experts on this subject based on the ideXlab platform.
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gas chromatography Multiphoton Ionization time of flight mass spectrometry using a femtosecond laser
Analytical and Bioanalytical Chemistry, 2013Co-Authors: Totaro ImasakaAbstract:A laser can be used for the selective excitation and subsequent Ionization of a molecule with an absorption band at the laser wavelength. This technique of Multiphoton Ionization (MPI), when combined with time-of-flight mass spectrometry (TOF-MS), permits the efficient detection of induced ions in mass analysis. This combination of MPI/TOF-MS can be coupled with gas chromatography (GC) to achieve even more enhanced selectivity. Thus, GC/MPI/TOF-MS can be employed for trace analysis of samples containing numerous chemical species. A variety of laser sources have been used for this purpose. Since molecules that are classified as environmental pollutants frequently contain chlorine and bromine atoms, the lifetime of the excited state can be decreased by energy transfer from the singlet to triplet levels by spin–orbit interaction. A high-power femtosecond laser with a pulse width shorter than the lifetime of the analyte molecule provides femtogram or even subfemtogram detection limits, which have not yet been achieved using the most sensitive high-resolution double-focus sector-type mass spectrometers. Numerous environmental pollutants such as dioxins in soils and pesticides in foods have been successfully quantified using GC/MPI/TOF-MS, and this technique has proven itself to be a useful and practical method for trace analysis.
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analysis of persistent organic pollutants at sub femtogram levels using a high power picosecond laser for Multiphoton Ionization in conjunction with gas chromatography time of flight mass spectrometry
Analytical Sciences, 2012Co-Authors: Taiki Matsui, Kodai Fukazawa, Masatoshi Fujimoto, Totaro ImasakaAbstract:A low-energy, high-repetition-rate picosecond laser (40 µJ, 20 kHz, 258 nm) was used for Multiphoton Ionization (MPI) in gas chromatography/time-of-flight mass spectrometry to quantitatively determine dioxins (DXNs) and polycyclic aromatic hydrocarbons (PAHs). The sensitivity of the technique was compared with that obtained using a high-energy, low-repetition-rate femtosecond laser (86 µJ, 1 kHz, 261 nm). The limits of detection (LODs) for the picosecond laser were several femtograms for chlorinated DXNs with low numbers of chloro substituents, and were several times lower than values obtained using a femtosecond laser, although the LODs were increased, reaching values that were nearly identical to those for the femtosecond laser for octachlorodibenzo-p-dioxin (octaCDD) and octachlorodibenzofuran (octaCDF). The LODs were also measured for 16 PAHs specified by the United States Environmental Protection Agency; the values for half of these compounds were at sub-femtogram levels. The procedure was used to analyze a surface-water sample collected from a river.