Marius Cristian Stroe | University of Bucharest (original) (raw)

Papers by Marius Cristian Stroe

Physics Letters A, 2001

We calculate resonances, antibound states and two new light induced states of the dressed one-dim... more We calculate resonances, antibound states and two new light induced states of the dressed one-dimensional attractive δfunction potential, as function of α 0-the free electron quiver motion amplitude in a monochromatic electromagnetic field, in the range 0 < α 0 < 150 a.u. We describe also our method, adequate to the numerical solution of the Schrödinger equation for this particular potential.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2011

We have studied the electron impact dissociation of vibrationally excited H+2. A distribution of ... more We have studied the electron impact dissociation of vibrationally excited H+2. A distribution of initial vibrational states given by the overlap factors between the vibrational ground state of H2 and different vibrational levels of H+2 has been considered. It was found that the relative contributions of the initial vibrational levels to the dissociative excitation cross section mimic the vibrational distribution

The European Physical Journal D, 2011

We have investigated the competition between dissociative excitation, dissociative recombination ... more We have investigated the competition between dissociative excitation, dissociative recombination and vibrational excitation processes taking place in the reactive collisions of vibrationally cold HD + with electrons. The energy range 1-12 eV has been considered.

Physical Review A, 2005

... Rev. A 53, 2513 (1996) [SPIN];[INSPEC];[CAS]. M. Stroe, M. Boca, V. Dinu, and V. Florescu, La... more ... Rev. A 53, 2513 (1996) [SPIN];[INSPEC];[CAS]. M. Stroe, M. Boca, V. Dinu, and V. Florescu, Laser Phys. 13, 1149 (2003). I. Simbotin, M. Stroe, and M. Gavrila, Laser Phys. ... Rev. A 53, 2513 (1996). [11] M. Stroe, M. Boca, V. Dinu, and V. Florescu, Laser Phys. 13, 1149 (2003). ...

Physica Scripta

Within time-dependent Hartree–Fock theory, we study the CO ionization for six different photon wa... more Within time-dependent Hartree–Fock theory, we study the CO ionization for six different photon wavelengths running from 200 to 700 nm. The parallel and perpendicular alignments of the CO molecular axis with the polarization direction of the laser electric field are considered for two different laser intensities, namely 1.0×1014 and 1.0×1015 W cm−2. At the laser intensity 1.0×1014 W cm−2, the ionization picture is characterized by the dominance of the highest occupied molecular orbital, while at laser intensity 1.0×1015 W cm−2 the inner valence molecular orbitals significantly contribute to the CO ionization. The present computations also reveal that orbital switching effects due to peak intensity variation may occur at some shorter wavelengths.

Journal of Physics B: Atomic, Molecular and Optical Physics

Competing processes (namely, dissociative recombination, vibrational excitation and vibrational d... more Competing processes (namely, dissociative recombination, vibrational excitation and vibrational de-excitation) taking place in the collisions between slow electrons and hydroxyl cations have been investigated for electron energies below 1 eV in the framework of the multichannel quantum defect theory. Rydberg states converging to the lowest excited ionic core have been included in some computations reported here.

Optik

Abstract The single ionization of HCl (X1Σ+) molecules in few-cycle intense laser pulses at 800 n... more Abstract The single ionization of HCl (X1Σ+) molecules in few-cycle intense laser pulses at 800 nm has been studied for laser intensities ranging from 2 × 1013 to 1.4 × 1014 W/cm2. Total and partial ionization probabilities were computed in the framework of the time-dependent Hartree-Fock theory. The influence of the laser pulse duration and the carrier envelope phase on the HCl ionization was investigated.

Journal of Physics B: Atomic, Molecular and Optical Physics

The dissociative recombination and vibrational excitation processes induced by electron impact on... more The dissociative recombination and vibrational excitation processes induced by electron impact on vibrationally cold are investigated in the framework of the multichannel quantum defect theory for electron energies below 1 eV. The thermal rate coefficients for the electron temperature range from 10 to 5000 K are reported.

Physical Review a, Sep 1, 2008

The Floquet problem for the interaction of an atom with a monochromatic laser field of frequency ... more The Floquet problem for the interaction of an atom with a monochromatic laser field of frequency omega was studied long ago for the case of high omega and arbitrary intensity using the ``high-frequency Floquet theory'' (HFFT). The two parameters of the theory are the frequency omega and the classical excursion parameter alpha0≡E0omega-2 , where E0 is the electric field strength. HFFT solves the Floquet system by successive iterations. Convergence of the iteration procedure was shown to be ensured by the condition that omega be suffiently large with respect to some typical atomic excitation energy. We now establish that the same iteration procedure is capable of handling the case of low frequency at sufficiently high intensity. This leads to the conclusion that in this case the ionization rates display quasistationary stabilization also at low omega . The concept is thus not exclusively related to high frequencies, as widely assumed. In addition, it suggests that a more appropriate designation for the theory should be ``high-intensity, high-frequency Floquet theory'' (HIHFFT). Our general results are applied to a frequently used one-dimensional (1D) soft-core potential model, for which explicit analytic results can be obtained for the quasienergies and wave functions from the general HIHFFT formulas. The relevance of these quasistationary results for the case of laser pulses is pointed out.

Laser Physics, Apr 1, 2004

ABSTRACT Quasistationary (adiabatic) stabilization (QS) and atomic dichotomy have been considered... more ABSTRACT Quasistationary (adiabatic) stabilization (QS) and atomic dichotomy have been considered as high-frequency concepts. We now show analytically and numerically that they apply also at low frequencies, on condition that the intensity is sufficiently high. The derivation is based on the iteration procedure developed earlier within the nonrelativistic high-frequency Floquet theory (HFFT) for the physical 3D hydrogen atom. We show that the successive iterations yielding the quasienergy E equivalent to W - (i/2)Gamma converge not only at large omega and arbitrary intensity (or excursion alpha(0)), which is the HFFT case, but also at sufficiently large alpha(0) and arbitrary omega. As a consequence, for linear polarization, at large alpha(0), the energies W(alpha(0)) have the familiar decrease of alpha(0)(-2/3) towards some threshold nomega, the atomic structure displays dichotomy, and the Gamma undergo QS. This shows that the iteration procedure is, in fact, a high-frequency, high-intensity Floquet theory (HI-HFFT). The general 3D results are illustrated numerically on a 1D model with a soft-core Coulomb potential. We have computed accurate Floquet quasienergies E(alpha(0)) for the lowest 18 states from alpha(0) = 0 to 100 at two low frequencies omega. It is for the first time that such an extended range of alpha(0) has been covered by a Floquet calculation. We show that the results for W(alpha(0)) and Gamma(alpha(0)) are in agreement with the predictions of HI-HFFT. In particular, F(alpha(0)) tends to zero (albeit in an oscillatory manner), thereby displaying QS. Dichotomy is illustrated by studying the behavior of the components of the Floquet solution. In view of the possibility of expanding atomic wave packets in terms of superpositions of Floquet states, the dynamical conclusion of our result is that one-electron systems become stable in superintense fields of any frequency within nonrelativistic theory.

Laser Physics

The two-photon ionization of the ground state hydrogen atom by two or three laser beams of the sa... more The two-photon ionization of the ground state hydrogen atom by two or three laser beams of the same frequency and direction of propagation, but different polarization states, is analyzed. Numerical results obtained via a perturbative calculation illustrate the influence of the relative intensity and of the phase difference on the differential ionization rate. Changes caused by these parameters in the alignment and asymmetries of the azimuthal angular distribution are emphasized.

Laser Physics

We consider the two-color ionization of the ground state hydrogen atom by an electromagnetic fiel... more We consider the two-color ionization of the ground state hydrogen atom by an electromagnetic field consisting of a coherent superposition of the fundamental frequency of an UV laser and its third harmonic, with a constant relative phase. We analyze the ionization process due to the net absorption of the energy 3∞ω. In the intensity regime investigated here, the final continuum state is reached by the interference of two different routes: (i) the absorption of one photon from the third harmonic and (ii) the absorption of three laser photons. The influence of the harmonic phase and of the field intensity on the azimuthal angular distribution of photoelectrons is analyzed. Dichroic effects are also emphasized.

Central European Journal of Physics, 2004

We study the two-photon ionization of the hydrogen atom from its ground state by a three-color el... more We study the two-photon ionization of the hydrogen atom from its ground state by a three-color electromagnetic field consisting of a superposition of an IR laser and two of its consecutive odd harmonics of order 2p−1 and 2p+1, withp a positive integer and constant relative phase difference. The ionization process due to the net absorption of the energy 2pħω (ω being the IR laser frequency) is considered. The influence of phase difference and helicity on the azimuthal angular distribution of the ejected photoelectrons is illustrated in the case in which the two harmonics have identical polarizations. Phase effect on the alignment of the differential ionization rate is also investigated.

Physica Scripta, 2008

ABSTRACT In the framework of the multi-channel quantum defect theory (MQDT), we have performed no... more ABSTRACT In the framework of the multi-channel quantum defect theory (MQDT), we have performed nonrotational computations for the dissociative excitation cross section of HD+ initially in the vibrational level vi+ (vi+=0, vi+=1 or vi+=2) of the electronic ground state, with electrons of energy ranging from 2 to 12 eV. Considering the case of energy-independent interactions, the reaction matrix K is evaluated in the second order of the Born expansion of the Lippmann–Schwinger equation.

Physics Letters A, 2009

ABSTRACT Present computations refer to the dissociative recombination and excitation of H2+, HD+H... more ABSTRACT Present computations refer to the dissociative recombination and excitation of H2+, HD+HD+ and HT+HT+ with electrons of energy above the dissociation limit of the ground state. A wave packet discretization method is used to describe the vibrational continua of the electronic states of the molecular cations. Assuming the energy-independent electronic interactions, this nonrotational MQDT approach is based on a second-order Born expansion of the reaction matrix.

Physics Letters A, 2001

We calculate resonances, antibound states and two new light induced states of the dressed one-dim... more We calculate resonances, antibound states and two new light induced states of the dressed one-dimensional attractive δfunction potential, as function of α 0-the free electron quiver motion amplitude in a monochromatic electromagnetic field, in the range 0 < α 0 < 150 a.u. We describe also our method, adequate to the numerical solution of the Schrödinger equation for this particular potential.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2011

We have studied the electron impact dissociation of vibrationally excited H+2. A distribution of ... more We have studied the electron impact dissociation of vibrationally excited H+2. A distribution of initial vibrational states given by the overlap factors between the vibrational ground state of H2 and different vibrational levels of H+2 has been considered. It was found that the relative contributions of the initial vibrational levels to the dissociative excitation cross section mimic the vibrational distribution

The European Physical Journal D, 2011

We have investigated the competition between dissociative excitation, dissociative recombination ... more We have investigated the competition between dissociative excitation, dissociative recombination and vibrational excitation processes taking place in the reactive collisions of vibrationally cold HD + with electrons. The energy range 1-12 eV has been considered.

Physical Review A, 2005

... Rev. A 53, 2513 (1996) [SPIN];[INSPEC];[CAS]. M. Stroe, M. Boca, V. Dinu, and V. Florescu, La... more ... Rev. A 53, 2513 (1996) [SPIN];[INSPEC];[CAS]. M. Stroe, M. Boca, V. Dinu, and V. Florescu, Laser Phys. 13, 1149 (2003). I. Simbotin, M. Stroe, and M. Gavrila, Laser Phys. ... Rev. A 53, 2513 (1996). [11] M. Stroe, M. Boca, V. Dinu, and V. Florescu, Laser Phys. 13, 1149 (2003). ...

Physica Scripta

Within time-dependent Hartree–Fock theory, we study the CO ionization for six different photon wa... more Within time-dependent Hartree–Fock theory, we study the CO ionization for six different photon wavelengths running from 200 to 700 nm. The parallel and perpendicular alignments of the CO molecular axis with the polarization direction of the laser electric field are considered for two different laser intensities, namely 1.0×1014 and 1.0×1015 W cm−2. At the laser intensity 1.0×1014 W cm−2, the ionization picture is characterized by the dominance of the highest occupied molecular orbital, while at laser intensity 1.0×1015 W cm−2 the inner valence molecular orbitals significantly contribute to the CO ionization. The present computations also reveal that orbital switching effects due to peak intensity variation may occur at some shorter wavelengths.

Journal of Physics B: Atomic, Molecular and Optical Physics

Competing processes (namely, dissociative recombination, vibrational excitation and vibrational d... more Competing processes (namely, dissociative recombination, vibrational excitation and vibrational de-excitation) taking place in the collisions between slow electrons and hydroxyl cations have been investigated for electron energies below 1 eV in the framework of the multichannel quantum defect theory. Rydberg states converging to the lowest excited ionic core have been included in some computations reported here.

Optik

Abstract The single ionization of HCl (X1Σ+) molecules in few-cycle intense laser pulses at 800 n... more Abstract The single ionization of HCl (X1Σ+) molecules in few-cycle intense laser pulses at 800 nm has been studied for laser intensities ranging from 2 × 1013 to 1.4 × 1014 W/cm2. Total and partial ionization probabilities were computed in the framework of the time-dependent Hartree-Fock theory. The influence of the laser pulse duration and the carrier envelope phase on the HCl ionization was investigated.

Journal of Physics B: Atomic, Molecular and Optical Physics

The dissociative recombination and vibrational excitation processes induced by electron impact on... more The dissociative recombination and vibrational excitation processes induced by electron impact on vibrationally cold are investigated in the framework of the multichannel quantum defect theory for electron energies below 1 eV. The thermal rate coefficients for the electron temperature range from 10 to 5000 K are reported.

Physical Review a, Sep 1, 2008

The Floquet problem for the interaction of an atom with a monochromatic laser field of frequency ... more The Floquet problem for the interaction of an atom with a monochromatic laser field of frequency omega was studied long ago for the case of high omega and arbitrary intensity using the ``high-frequency Floquet theory'' (HFFT). The two parameters of the theory are the frequency omega and the classical excursion parameter alpha0≡E0omega-2 , where E0 is the electric field strength. HFFT solves the Floquet system by successive iterations. Convergence of the iteration procedure was shown to be ensured by the condition that omega be suffiently large with respect to some typical atomic excitation energy. We now establish that the same iteration procedure is capable of handling the case of low frequency at sufficiently high intensity. This leads to the conclusion that in this case the ionization rates display quasistationary stabilization also at low omega . The concept is thus not exclusively related to high frequencies, as widely assumed. In addition, it suggests that a more appropriate designation for the theory should be ``high-intensity, high-frequency Floquet theory'' (HIHFFT). Our general results are applied to a frequently used one-dimensional (1D) soft-core potential model, for which explicit analytic results can be obtained for the quasienergies and wave functions from the general HIHFFT formulas. The relevance of these quasistationary results for the case of laser pulses is pointed out.

Laser Physics, Apr 1, 2004

ABSTRACT Quasistationary (adiabatic) stabilization (QS) and atomic dichotomy have been considered... more ABSTRACT Quasistationary (adiabatic) stabilization (QS) and atomic dichotomy have been considered as high-frequency concepts. We now show analytically and numerically that they apply also at low frequencies, on condition that the intensity is sufficiently high. The derivation is based on the iteration procedure developed earlier within the nonrelativistic high-frequency Floquet theory (HFFT) for the physical 3D hydrogen atom. We show that the successive iterations yielding the quasienergy E equivalent to W - (i/2)Gamma converge not only at large omega and arbitrary intensity (or excursion alpha(0)), which is the HFFT case, but also at sufficiently large alpha(0) and arbitrary omega. As a consequence, for linear polarization, at large alpha(0), the energies W(alpha(0)) have the familiar decrease of alpha(0)(-2/3) towards some threshold nomega, the atomic structure displays dichotomy, and the Gamma undergo QS. This shows that the iteration procedure is, in fact, a high-frequency, high-intensity Floquet theory (HI-HFFT). The general 3D results are illustrated numerically on a 1D model with a soft-core Coulomb potential. We have computed accurate Floquet quasienergies E(alpha(0)) for the lowest 18 states from alpha(0) = 0 to 100 at two low frequencies omega. It is for the first time that such an extended range of alpha(0) has been covered by a Floquet calculation. We show that the results for W(alpha(0)) and Gamma(alpha(0)) are in agreement with the predictions of HI-HFFT. In particular, F(alpha(0)) tends to zero (albeit in an oscillatory manner), thereby displaying QS. Dichotomy is illustrated by studying the behavior of the components of the Floquet solution. In view of the possibility of expanding atomic wave packets in terms of superpositions of Floquet states, the dynamical conclusion of our result is that one-electron systems become stable in superintense fields of any frequency within nonrelativistic theory.

Laser Physics

The two-photon ionization of the ground state hydrogen atom by two or three laser beams of the sa... more The two-photon ionization of the ground state hydrogen atom by two or three laser beams of the same frequency and direction of propagation, but different polarization states, is analyzed. Numerical results obtained via a perturbative calculation illustrate the influence of the relative intensity and of the phase difference on the differential ionization rate. Changes caused by these parameters in the alignment and asymmetries of the azimuthal angular distribution are emphasized.

Laser Physics

We consider the two-color ionization of the ground state hydrogen atom by an electromagnetic fiel... more We consider the two-color ionization of the ground state hydrogen atom by an electromagnetic field consisting of a coherent superposition of the fundamental frequency of an UV laser and its third harmonic, with a constant relative phase. We analyze the ionization process due to the net absorption of the energy 3∞ω. In the intensity regime investigated here, the final continuum state is reached by the interference of two different routes: (i) the absorption of one photon from the third harmonic and (ii) the absorption of three laser photons. The influence of the harmonic phase and of the field intensity on the azimuthal angular distribution of photoelectrons is analyzed. Dichroic effects are also emphasized.

Central European Journal of Physics, 2004

We study the two-photon ionization of the hydrogen atom from its ground state by a three-color el... more We study the two-photon ionization of the hydrogen atom from its ground state by a three-color electromagnetic field consisting of a superposition of an IR laser and two of its consecutive odd harmonics of order 2p−1 and 2p+1, withp a positive integer and constant relative phase difference. The ionization process due to the net absorption of the energy 2pħω (ω being the IR laser frequency) is considered. The influence of phase difference and helicity on the azimuthal angular distribution of the ejected photoelectrons is illustrated in the case in which the two harmonics have identical polarizations. Phase effect on the alignment of the differential ionization rate is also investigated.

Physica Scripta, 2008

ABSTRACT In the framework of the multi-channel quantum defect theory (MQDT), we have performed no... more ABSTRACT In the framework of the multi-channel quantum defect theory (MQDT), we have performed nonrotational computations for the dissociative excitation cross section of HD+ initially in the vibrational level vi+ (vi+=0, vi+=1 or vi+=2) of the electronic ground state, with electrons of energy ranging from 2 to 12 eV. Considering the case of energy-independent interactions, the reaction matrix K is evaluated in the second order of the Born expansion of the Lippmann–Schwinger equation.

Physics Letters A, 2009

ABSTRACT Present computations refer to the dissociative recombination and excitation of H2+, HD+H... more ABSTRACT Present computations refer to the dissociative recombination and excitation of H2+, HD+HD+ and HT+HT+ with electrons of energy above the dissociation limit of the ground state. A wave packet discretization method is used to describe the vibrational continua of the electronic states of the molecular cations. Assuming the energy-independent electronic interactions, this nonrotational MQDT approach is based on a second-order Born expansion of the reaction matrix.