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Auger effect in the presence of strong x-ray pulses
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).ORCID iD: 0000-0002-1763-9383
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2010 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, ISSN 1050-2947, Vol. 81, no 4, 043412- p.Article in journal (Refereed) Published
Abstract [en]

We study the role of propagation of strong x-ray free-electron laser pulses on the Auger effect. When the system is exposed to a strong x-ray pulse the stimulated emission starts to compete with the Auger decay. As an illustration we present numerical results for Ar gas with the frequency of the incident x-ray pulse tuned in the 2p(3/2)-4s resonance. It is shown that the pulse propagation is accompanied by two channels of amplified spontaneous emission, 4s-2p(3/2) and 3s-2p(3/2), which reshape the pulse when the system is inverted. The population inversion is quenched for longer propagation distances where lasing without inversion enhances the Stokes component. The results of simulations show that the propagation of the strong x-ray pulses affect intensively the Auger branching ratio.

Place, publisher, year, edition, pages
2010. Vol. 81, no 4, 043412- p.
Keyword [en]
Amplified spontaneous emissions, Auger decays, Auger effects, Branching ratio, Lasing without inversion, Numerical results, Population inversions, Propagation distances, Pulse propagation, Stokes component, Two channel, X ray pulse, X-ray free electron lasers
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-14258DOI: 10.1103/PhysRevA.81.043412ISI: 000277227300128Scopus ID: 2-s2.0-77951125476OAI: oai:DiVA.org:kth-14258DiVA: diva2:331940
Funder
Swedish Research CouncilCarl Tryggers foundation
Note

QC 20100728

Available from: 2010-07-28 Created: 2010-07-28 Last updated: 2014-04-11Bibliographically 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
2. Spontaneous and stimulated X-ray Raman scattering
Open this publication in new window or tab >>Spontaneous and stimulated X-ray Raman scattering
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis is devoted to theoretical studies of resonant X-ray scattering and propagation of strong X-ray pulses. In the first part of the thesis the nuclear dynamics of different molecules is studied using resonant X-ray Raman and resonant Auger scattering techniques. We show that the shortening of the scattering duration by the detuning results in a purification of the Raman spectra from overtones and soft vibrational modes. The simulations are in a good agreement with measurements, performed at the MAX-II and the Swiss Light Source with vibrational resolution. We explain why the scattering to the ground state nicely displays the vibrational structure of liquid acetone in contrast to excited final state. Theory of resonant X-ray scattering by liquids is developed. We show that, contrary to aqueous acetone, the environmental broadening in pure liquid acetone is twice smaller than the broadening by soft vibrational modes significantly populated at room temperature. Similar to acetone, the "elastic" band of X-ray Raman spectra of molecular oxygen is strongly affected by the Thomson scattering. The Raman spectrum demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the oxygen atoms separate. It is found that the vibrational scattering anisotropy caused by the interference of the "inelastic" Thomson and resonant scattering channels in O2. A new spin selection rule is established in inelastic X-ray Raman spectra of O2. It is shown that the breakdown of the symmetry selection rule based on the parity of the core hole, as the core hole and excited electron swap parity. Multimode calculations explain the two thresholds of formation of the resonant Auger spectra of the ethene molecule by the double-edge structure of absorption spectrum caused by the out-of- and in-plane modes. We predict the rotational Doppler effect and related broadening of X-ray photoelectron and resonant Auger spectra, which has the same magnitude as its counterpart-the translational Doppler effect. The second part of the thesis explores the interaction of the medium with strong X-ray free-electron laser (XFEL) fields. We perform simulations of nonlinear propagation of femtosecond XFEL pulses in atomic vapors by solving coupled Maxwell's and density matrix equations. We show that self-seeded stimulated X-ray Raman scattering strongly influences the temporal and spectral structure of the XFEL pulse. The generation of Stokes and four-wave mixing fields starts from the seed field created during pulse propagation due to the formation of extensive ringing pattern with long spectral tail. We demonstrate a compression into the attosecond region and a slowdown of the XFEL pulse up to two orders of magnitude. In the course of pulse propagation, the Auger yield is strongly suppressed due to the competitive channel of stimulated emission. We predict a strong X-ray fluorescence from the two-core-hole states of Ne created in the course of the two-photon X-ray absorption.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. viii, 71 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2011:8
Keyword
resonant X-ray scattering, resonant Auger scattering, rotational Doppler broadening, XFEL pulse
National Category
Atom and Molecular Physics and Optics Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-32859 (URN)978-91-7415-925-7 (ISBN)
Public defence
2011-05-13, FA32, AlbaNova, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110426Available from: 2011-04-26 Created: 2011-04-21 Last updated: 2011-11-23Bibliographically approved

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