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Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Theoretical Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Theoretical Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Theoretical Chemistry)
2008 (English)In: Chinese Physics (Beijing), ISSN 1009-1963, E-ISSN 1741-4199, Vol. 17, no 11, p. 4211-4217Article in journal (Refereed) Published
Abstract [en]

This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultras short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 40-bis(dimethylamino) stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.

Place, publisher, year, edition, pages
2008. Vol. 17, no 11, p. 4211-4217
Keywords [en]
superfluorescence; ultra-short laser pulse; 4, 4 '-bis(dimethylamino) stilbene organic molecule; Maxwell-Bloch equations
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-11457DOI: 10.1088/1674-1056/17/11/043ISI: 000261206700043Scopus ID: 2-s2.0-62649152347OAI: oai:DiVA.org:kth-11457DiVA, id: diva2:276736
Note
QC 20100729Available 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. p. x, 76
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2009:25
Keywords
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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