Publications
241 results found
Matusek DR, Ivanov MY, Wright JS, 1998, Selectivity in intense field dissociation, CHEMICAL PHYSICS LETTERS, Vol: 284, Pages: 247-253, ISSN: 0009-2614
Strong laser fields exert forces comparable to, or exceeding, the forces which bind atoms to molecules. We exploit this physics to achieve selectivity in the dissociation of triatomic cations, using a simple, intuitive approach. We propose a class of molecules for which a strong bond can be preferentially dissociated over a weak bond using a strong infrared pulse with very simple pulse parameters. Selectivity is demonstrated for a model system of the type ABC(+). (C) 1998 Elsevier Science B.V.
Sakai H, Stapelfeldt H, Constant E, et al., 1998, Metastable triply charged diatomic molecules produced with femtosecond pulses, PHYSICAL REVIEW LETTERS, Vol: 81, Pages: 2217-2220, ISSN: 0031-9007
We show that ultrashort pulse strong field multiphoton ionization efficiently produces metastable highly charged molecules such as metastable diatomic trications I-2(3+), Br-2(3+), and Cl-2(3+). The efficiency of stable trication production decreases rapidly with increasing pulse duration. Weak pre- or post-pulse irradiation also prevents efficient production or survival of trications, We propose strong-field femtosecond Raman spectroscopy to determine trication vibrational frequencies.
Thachuk M, Ivanov MY, Wardlaw DM, 1998, A semiclassical approach to intense-field above-threshold dissociation in the long wavelength limit. II. Conservation principles and coherence in surface hopping, JOURNAL OF CHEMICAL PHYSICS, Vol: 109, Pages: 5747-5760, ISSN: 0021-9606
This paper is a companion to our recently published semiclassical formalism for treating time-dependent Hamiltonians [J. Chem. Phys, 105, 4094 (1996)], which was applied to study the dissociation of diatomic ions in intense laser fields. Here two fundamental issues concerning this formalism are discussed in depth: conservation principles and coherence. For time-dependent Hamiltonians, the conservation principle to apply during a trajectory hop depends upon the physical origin of the electronic transition, with total energy conservation and nuclear momentum conservation representing the two limiting cases. It is shown that a]applying an inappropriate scheme leads to unphysical features in the kinetic energy of the dissociation products. A method is introduced that smoothly bridges the two limiting cases and applies the physically justified conservation scheme at all times. It is also shown that the semiclassical formalism can predict erroneous results if the electronic amplitudes for well-separated hops are added coherently. This is a fundamental problem with the formalism which leads to unphysical results if left unattended. Alternative schemes are introduced for dealing with this problem and their accuracies are assessed. Generalization of the well-known Landau-Zener formula to the time-dependent Hamiltonian case is derived, which allows one to significantly decrease the computational overhead involved with the numerical implementation of the semiclassical method. Finally, we show that in strong-field molecular dissociation a trajectory can ”surf“ a moving avoided crossing. In this case the hopping probability is a sensitive function of the interference between two closely spaced avoided crossing regions. (C) 1998 American Institute of Physics.
Ivanov MY, Krainov VP, 1998, Theory of quantum defect for Rydberg states of alkali atoms, Spectroscopy of Autoionizing States of Atoms and Ions, Editors: Safronova
Corkum PB, Ivanov MY, Wright JS, 1997, Subfemtosecond processes in strong laser fields, ANNUAL REVIEW OF PHYSICAL CHEMISTRY, Vol: 48, Pages: 387-406, ISSN: 0066-426X
Strong field atomic and molecular interactions can be understood by following electronic dynamics inside the laser cycle. This quasistatic perspective introduces the subfemtosecond time scale into strong-field dynamics through time-dependent Born-Oppenheimer surfaces. We discuss both theoretical and experimental results in atomic and molecular ionization and dissociation with applications to femtochemistry. An all-optical Coulomb explosion method for determining time-dependent molecular structure and properties is demonstrated. The concept of time-dependent Born-Oppenheimer surfaces is used to study molecular dissociation and exchange reactions in infrared fields.
Ivanov MY, Stolow A, 1997, Coherent control of high-n Rydberg lifetimes using wavepacket technology, CHEMICAL PHYSICS LETTERS, Vol: 265, Pages: 231-238, ISSN: 0009-2614
We describe a simple, experimentally feasible scheme for enhancing lifetimes of high-n Rydberg states. We propose a new control scheme, based upon a ’wavepacket technology’ which uses time-dependent, crossed electric and magnetic fields. Model (hydrogenic) calculations illustrating the control over l and m quantum numbers are presented and experimental parameters are suggested. The effects of core multipole moments on the decay of the target state (high l, high m) are discussed. Coherent lifetime enhancement should be applicable to small signal zero-kinetic-energy (ZEKE) photoelectron spectroscopy experiments and to Rydberg photofragment translational energy spectroscopy.
Haljan P, Ivanov MY, Corkum PB, 1997, Laser control of electron localization in molecules and double quantum wells, LASER PHYSICS, Vol: 7, Pages: 839-843, ISSN: 1054-660X
Two problems are addressed in this paper. First, we describe how electron localization (also known as coherent destruction of tunneling) can be used to control dissociation of homonuclear diatomic molecular ions (e.g., H-2(+)) with intense few-cycle pulses. Second, we show how electron tunneling and its localization in one of the wells of a double-well potential can be controlled using a two-color light with frequencies omega and 2 omega.
Dietrich P, Ivanov MY, 1997, Two-electron dissociative ionization of H-2 and D-2 in strong infrared fields, MULTIPHOTON PROCESSES 1996, Pages: 202-210, ISSN: 0951-3248
We present a quantitative physical model of above-threshold dissociation of homonuclear molecular ions in intense mid-infrared laser fields. This allows us to self-consistently describe all three processes that occur during dissociative ionization of H-2 and D-2 (ionization of the neutral molecule, dissociation of the molecular ion, and its secondary ionization) using a semiclassical approach. The kinetic energy spectrum of the dissociating fragments is obtained and analysed.
Ivanov MY, Brabec T, Burnett N, 1996, Coulomb corrections and polarization effects in high-intensity high-harmonic emission, PHYSICAL REVIEW A, Vol: 54, Pages: 742-745, ISSN: 1050-2947
We describe a quasiclassical approach to correct electron motion following tunneling ionization in intense laser fields, for the presence of the Coulomb potential. The technique is applied to model the dependence of high-harmonic generation on the ellipticity of the incident laser field. We present experimental data on the harmonics with photon energies close to the ionization potential of an atom, identify their source, and explain their unusual dependence on the ellipticity of the incident laser field. Our calculations are in good agreement with experimental data.
Ivanov MY, Matusek DR, Wright JS, 1996, Altered reaction dynamics: Lowered barriers and bound states induced by intense infrared laser fields, CHEMICAL PHYSICS LETTERS, Vol: 255, Pages: 232-237, ISSN: 0009-2614
This Letter reports a study on the effect of the Stark shift for exchange reactions in intense infrared laser fields. It is shown for the H + H-2 exchange reaction that such fields reduce the potential barrier, thus enhancing the reaction rate at low temperatures. Another interesting effect, caused by the change in molecular polarizability as reactants approach, is the creation of (laser-induced) potential minima along the reaction path.
Dietrich P, Ivanov MY, Ilkov FA, et al., 1996, Two-electron dissociative ionization of H-2 and D-2 in infrared laser fields, PHYSICAL REVIEW LETTERS, Vol: 77, Pages: 4150-4153, ISSN: 0031-9007
We present a quantitative physical model of above-threshold dissociation of homonuclear molecular ions in intense midinfrared laser fields. This allows us to describe self-consistently all three processes that occur during dissociative ionization of H-2 and D-2 (ionization of the neutral molecule, dissociation of the molecular ion, and its secondary ionization) using a semiclassical approach. The kinetic energy spectrum of the dissociating fragments is obtained and analyzed.
Corkum P, Ivanov MY, 1996, Ultrafast VUV lasers eye first commercial applications, PHOTONICS SPECTRA, Vol: 30, Pages: 104-105, ISSN: 0731-1230
Brabec T, Ivanov MY, Corkum PB, 1996, Coulomb focusing in intense field atomic processes, PHYSICAL REVIEW A, Vol: 54, Pages: R2551-R2554, ISSN: 1050-2947
In the intense field (long-wavelength) limit, the oscillating motion of an electron wave packet leads to multiple passes by the scattering Coulomb center. The influence of the Coulomb focusing, in combination with multiple returns, focuses parts of the electron wave function, increasing the efficiency of such intense field processes as multiphoton double ionization. Our calculations show enhancement by more than an order of magnitude for multiphoton double ionization of He at 0.8 mu m.
Ivanov MY, Matusek DR, Wright JS, 1996, Exchange reactions in intense infrared laser fields, PHYSICAL REVIEW A, Vol: 54, Pages: 5159-5170, ISSN: 1050-2947
We examine the role of the dipole moment induced by an intense nonresonant infrared laser field on exchange reactions of the type A + BC –> AB + C. This is compared to previous work which included the effect of the permanent dipole moment and its variation along the reaction coordinate. The formalism for laser-molecule interaction is developed for the cases where the reciprocal laser frequency is comparable to or much shorter than the time required for the system to cross the transition state. It is predicted that the induced dipole moment will both lower the electronic barrier to reaction and also create bound states along the reaction path. Results of classical trajectory calculations are presented for the collinear H + H-2 –> H + H reaction, using ab initio dipole moment and polarizability surfaces. It is found that the collisional energy threshold for reaction is lowered significantly, and that the effects of the induced dipole moment dominate over those of the permanent dipole moment. A time-dependent analysis of the reaction shows that the fluctuating barrier can occasionally be very low when the transition state is approached, allowing trajectories to be reactive with very low collision energies.
Villeneuve DM, Ivanov MY, Corkum PB, 1996, Enhanced ionization of diatomic molecules in strong laser fields: A classical model, PHYSICAL REVIEW A, Vol: 54, Pages: 736-741, ISSN: 1050-2947
A classical model is developed to study molecular ionization in strong laser fields. The model is compared with a one-dimensional quantum-mechanical model for the case of H-2(+). The intensity threshold for ionization of H-2(+) is studied as a function of laser polarization, wavelength, pulse duration, and internuclear separation. A range of internuclear separations is found where the ionization rate is enhanced over that at the equilibrium separation, in agreement with the quantum-mechanical model. The classical model is then extended to multielectron diatomic molecules. A regime is found where simultaneous two-electron ionization occurs. An intensity range is suggested for looking for enhanced ionization effects in dissociating diatomic molecules.
Thachuk M, Ivanov MY, Wardlaw DM, 1996, A semiclassical approach to intense-field above-threshold dissociation in the long wavelength limit, JOURNAL OF CHEMICAL PHYSICS, Vol: 105, Pages: 4094-4104, ISSN: 0021-9606
A new semiclassical Formalism has been developed to treat Hamiltonians having explicit time dependence with particular application to the dissociation of diatomic ions in intense laser fields. Based on this formalism, a hopping algorithm is presented which specifies how classical trajectories should be moved between coupled electronic surfaces. The theory is laid out in a rigorous, general form and an analysis is also presented for the case where only two electronic surfaces are strongly coupled. In addition, valuable physical insight into the hopping process is obtained by considering the theory in a number of physically relevant limiting cases. From this insight a number of guidelines are proposed which detail the manner in which trajectory hopping should be implemented when lime-dependent potential energy surfaces are present, including the effects of phase coherence and conservation principles. (C) 1996 American Institute of Physics.
Seideman T, Ivanov MY, Corkum PB, 1996, The use of intense-field ionization in time-resolved measurements, CHEMICAL PHYSICS LETTERS, Vol: 252, Pages: 181-188, ISSN: 0009-2614
We show that intense radiation introduces a length-scale in molecules which translates into a dramatic enhancement of the rate of multiple ionization of molecules at characteristic internuclear separations. This feature is common to a wide range of systems and is insensitive to variations in frequency and intensity. The electronic properties responsible for this effect are explored. We propose the use of the sensitivity of intense-field ionization to the molecular configuration as a probe in time-resolved studies of dissociative dynamics.
Matusek DR, Ivanov MY, Wright JS, 1996, IR laser enhancement of the H+H-2 reaction on an accurate dipole moment surface, CHEMICAL PHYSICS LETTERS, Vol: 258, Pages: 255-259, ISSN: 0009-2614
This Letter reports an accurate dipole moment surface for collinear H-3. Using this surface, we examine the H + H-2 reaction dynamics in infrared laser fields. IR laser light interacting with the system via the dipole moment (A.E. Orel and W.H. Miller, Chem. Phys. Lett. 57 (1978) 362) has no effect on the system at moderate intensitites (e.g. 10(12) W/cm(2)), and the interaction only becomes significant at higher intensities where other processes become important. However, the shape of the collinear reaction probability obtained by Orel and Miller using an assumed dipole surface shows remarkable agreement with the results obtained in this more quantitative study.
RZAZEWSKI K, IVANOV M, PUMARES L, et al., 1995, RADIATING COHERENT ATOMIC WAVE-PACKETS, LASER PHYSICS, Vol: 5, Pages: 451-460, ISSN: 1054-660X
Recent progress in the production and control of atomic wave packets calls for reexamination of the most fundamental quantum optical processes. We examined the evolution of the atomic wave packet resonantly driven by the monochromatic laser beam and the spontaneous emission from an extended atom. We stress the role of Doppler shifts in the dephasing of the atomic dipole. New effects of single-pulse photon echo, homogeneous Doppler modification of the emission line, and interference effects in the coherent part of the emission spectrum are discussed. We also present the emission spectra of an atom oscillating in a harmonic trap.
SEIDEMAN T, IVANOV M, CORKUM P, 1995, ROLE OF ELECTRON LOCALIZATION IN INTENSE-FIELD MOLECULAR IONIZATION, PHYSICAL REVIEW LETTERS, Vol: 75, Pages: 2819-2822, ISSN: 0031-9007
The rate of nonlinear ionization is strongly enhanced as a molecule is stretched beyond its equilibrium internuclear separation, reaching a peak rate that is many orders of magnitude greater than that at either small or large distances. The enhancement results from nonadiabatic electron localization near the nuclei and its presence is insensitive to the laser frequency and intensity. Most intense-field dissociative ionization experiments are influenced by this effect.
IVANOV M, BITOUK D, RZAZEWSKI K, et al., 1995, CLASSICAL CHAOS AND ITS QUANTUM MEASURES IN RYDBERG STATES OF MULTIELECTRON ATOMS, PHYSICAL REVIEW A, Vol: 52, Pages: 149-156, ISSN: 1050-2947
CORKUM P, DUPONT E, IVANOV M, 1995, APPLICATIONS OF WEAK AND STRONG-FIELD COHERENT CONTROL, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, Vol: 209, Pages: 84-PHYS, ISSN: 0065-7727
ZUO T, BANDRAUK A, IVANOV M, et al., 1995, CONTROL OF HIGH-ORDER HARMONIC-GENERATION IN STRONG LASER FIELDS, PHYSICAL REVIEW A, Vol: 51, Pages: 3991-3998, ISSN: 1050-2947
LEWENSTEIN M, BALCOU P, IVANOV M, et al., 1994, THEORY OF HIGH-HARMONIC GENERATION BY LOW-FREQUENCY LASER FIELDS, PHYSICAL REVIEW A, Vol: 49, Pages: 2117-2132, ISSN: 1050-2947
We present a simple, analytic, and fully quantum theory of high-harmonic generation by low-frequency laser fields. The theory recovers the classical interpretation of Kulander et al. in [Proceedings of the SILAP III Workshop, edited by B. Piraux (Plenum, New York, 1993)] and Corkum [Phys. Rev. Lett. 71, 1994 (1993)] and clearly explains why the single-atom harmonic-generation spectra fall off at an energy approximately equal to the ionization energy plus about three times the oscillation energy of a free electron in the field. The theory is valid for arbitrary atomic potentials and can be generalized to describe laser fields of arbitrary ellipticity and spectrum. We discuss the role of atomic dipole matrix elements, electron rescattering processes, and of depletion of the ground state. We present the exact quantum-mechanical formula for the harmonic cutoff that differs from the phenomenological law I(p) + 3.17U(p) where I(p) is the atomic ionization potential and U(p) is the ponderomotive energy, due to the account for quantum tunneling and diffusion effects.
IVANOV M, 1994, SUPPRESSION OF RESONANT MULTIPHOTON IONIZATION VIA RYDBERG STATES, PHYSICAL REVIEW A, Vol: 49, Pages: 1165-1170, ISSN: 1050-2947
We discuss atomic stabilization in the process of resonance ionization via Rydberg states. We show that a strong resonance interaction between Rydberg states and a low-lying state substantially suppresses ionization. :As a result, the population is trapped in the Rydberg states. Raman-type coupling of Rydberg states via the continuum is shown to be essential for the effect even when the bound-free interaction is weak.
Ivanov MY, Corkum PB, 1994, Symmetry breaking and the control of harmonics with strong short laser pulses, Super-Intense Laser-Atom Physics, Editors: Piraux, L'Hullier, Rzazewski, Publisher: Plenum Press, N.Y
CORKUM P, BURNETT N, IVANOV M, 1994, SUBFEMTOSECOND PULSES, OPTICS LETTERS, Vol: 19, Pages: 1870-1872, ISSN: 0146-9592
High-harmonic emission is very sensitive to the polarization of a fundamental laser beam. By combining two short perpendicularly polarized pulses with frequencies centered at omega(1) and omega(2), where (omega(1)-omega(2))/omega(1) much less than 1, we can create a pulse with polarization that sweeps from circular through linear back to circular. It is possible to make the duration of the segment of the pulse capable of emitting short-wavelength radiation so small that emission is possible only for a time less than the period of the fundamental.
Ivanov MY, Corkum PB, Dietrich P, et al., 1994, From high harmonics to strong field coherent control of atomic processes., Multiphoton Processes, Editors: Evans, Chin, Publisher: World Scientific
Lewenstein M, Salieres P, Ph B, et al., 1994, Where is the harmonic generation cutoff?, Editors: Evans, Chin, Publisher: World Scientific
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