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Coherent control of population and pulse propagation beyond the rotating wave approximation
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). (Theoretical Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). (Theoretical Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
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2008 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 7, 074016Article in journal (Refereed) Published
Abstract [en]

The dynamics of populations of the vibrational states in a NO molecule ( one-photon absorption) and of the electronic states in a 4,4'-bis( dimethylamino) stilbene molecule ( two-photon absorption) is studied versus the frequency, intensity and shape of the laser pulse. We show that specially designed infrared laser pulses can build selective populations of certain vibrational states. A detuning of light frequency from the vibrational resonance qualitatively changes the dynamics of populations. It is found out that the populations of the nonresonant levels follow the pulse shape adiabatically if the detuning significantly exceeds the inverse characteristic time of the change of the pulse. Depopulation of the nonresonant vibrational states leads to a high population of the resonant state at the end of the pulse. Complete breakdown of the standard rotating wave approximation for a two-photon absorption process is observed even for a rather small intensity of the laser pulse. An analytical solution for the interaction of a pulse with a three-level system beyond the rotating wave approximation is obtained, and it is in close agreement with the strict numerical solution of the amplitude equations. Special attention is paid to the population dynamics of randomly oriented molecules. The orientational disorder as well as the vibrations limit the coherent population transfer. Calculations show the strong role of the anisotropy of photoexcitation in the coherent control of populations which can affect the anisotropy of photobleaching.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2008. Vol. 41, no 7, 074016
Keyword [en]
self-induced transparency, 2-photon absorption, laser-pulses, basis-sets, density, exchange, behavior, bond
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-11454DOI: 10.1088/0953-4075/41/7/074016ISI: 000254778700017Scopus ID: 2-s2.0-42549157700OAI: oai:DiVA.org:kth-11454DiVA: diva2:276727
Note

QC 20100728

Available from: 2009-11-11 Created: 2009-11-11 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Dynamics of multiphoton processes in nonlinear optics and x-ray spectroscopy
Open this publication in new window or tab >>Dynamics of multiphoton processes in nonlinear optics and x-ray spectroscopy
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

New generations of ultrashort and intense laser pulses as well ashigh power synchrotron radiation sources and x-ray free electronlasers have promoted fast developments in nonlinear optics andx-ray spectroscopy.The new experimental achievements and the appearance of varieties of novelnonlinear phenomena call for further development of theories. The objective of this thesis is to develop and apply thetheories to explain existing experimental data and to suggest new experiments.

The first part of the thesis is devoted to nonlinear propagation of optical pulses. It is shown that the vibrational levels can be selectively populated by varying the duration, shape and intensity of the pump pulse. We obtained a strict analytical solution for the resonant two-photon interaction in a multilevel system beyond rotating wave approximation. Simulations show that the polarization anisotropy of the two-photon excitation affects strongly the anisotropy of photobleaching.The two-photon area theorem is reformulated with taking into account the dynamical Stark shift and the contribution from the permanent dipole moments. In general the dynamical Stark shift does not allow complete population of the excited state, but it can be compensated by detunings in atoms. A dynamical theory of the sequential two-photon absorption of  microsecond pulses  is developed to explore the role of transverse inhomogeneity of the light beam on optical limiting properties.  The propagation of ultrashort laser pulses in nondipolar and dipolar media is investigated with special attention to the generation of superfluorescence and supercontinuum and the formation of attosecond pulses.

The second part of the thesis addresses the interaction of molecules with x-ray radiation.  We explore here the role of nuclear dynamics in resonant Auger scattering. Multimode simulations of the Auger spectra of ethylene molecule explain the main spectral features of the experimental spectra and show that the spectral profiles are formed mainly due to six vibrational modes. We predict the Doppler splitting of the atomic peak in resonant Auger scattering from SF6 molecule for circularly polarized x-rays. This effect is confirmed by the recent experiment. A new scheme of x-ray pump-probe spectroscopy, namely, resonant inelastic x-ray scattering accompanied by core-hole hopping induced by strong laser fields is suggested. The laser-induced promotion of core holes opens the symmetry forbidden scattering channels and gives rise to new spectral lines in the x-ray scattering spectrum. The strength of the symmetry forbidden lines becomes strong when  the time of Rabi flopping is shorter than the lifetime of the core-excited state. We study the role of propagation of femtosecond x-ray free-electron pulses on the Auger process. Simulations show  that there exists a strong competition between Auger decay and stimulated emission. The Auger yield and Auger branching ratio are strongly suppressed in the course of pulse propagation.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. x, 76 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2009:25
Keyword
nonlinear optics, x-ray spectroscopy, multiphoton processes, pulse propagation
National Category
Atom and Molecular Physics and Optics Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-11394 (URN)978-91-7415-480-1 (ISBN)
Public defence
2009-12-09, FA32, Roslagstullsbacken 21, Albanova University Center, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100729Available from: 2009-11-11 Created: 2009-11-04 Last updated: 2010-07-29Bibliographically approved

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