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Optical limiting and pulse reshaping of picosecond pulse trains by fullerene C60
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Theoretical Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Theoretical Chemistry)
KTH, School of Biotechnology (BIO). (Theoretial Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
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2009 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, Vol. 174, 125-130 p.Article in journal (Refereed) Published
Abstract [en]

We present a dynamical theory of nonlinear absorption and propagation of a laser pulse train that contains 20 subpulses with an individual pulse width of loops. It is shown that the accumulative nonlinearity and the reverse saturation absorption play important roles in the optical limiting performance and pulse shaping. When the incident field is not too strong, the population transfer reveals a slow response process, and the periodic sequence of short light pulses can be regarded as a continuous long pulse. The general theory is applied to fullerence C-60, which is a popular reverse saturable absorption material and a good limiter because of its larger excited-state absorption cross-section compared with that of the ground state. The propagation of the front subpulses is mainly affected by the linear transition between the ground state and the first excited singlet state, while the latter subpulses are attenuated by the excited-state absorption. Moreover, these two different kinds of absorption mechanisms result in different radial distributions for different subpulses. The pulse propagation is studied by solving numerically the coupled rate equations and the propagation equation of the optical pulse intensity, using experimental parameters as input. We suggest a new method to measure the lifetime of the triplet state.

Place, publisher, year, edition, pages
2009. Vol. 174, 125-130 p.
Keyword [en]
Pulse trains; Optical limiting; Fullerence; Singlet-triplet
National Category
Industrial Biotechnology
Identifiers
URN: urn:nbn:se:kth:diva-11435DOI: 10.1016/j.elspec.2009.03.010ISI: 000271347700021Scopus ID: 2-s2.0-70349209130OAI: oai:DiVA.org:kth-11435DiVA: diva2:276058
Note
QC 20100713Available from: 2009-11-10 Created: 2009-11-10 Last updated: 2010-12-07Bibliographically approved
In thesis
1. Molecular electronic,  vibrational and rotational motion in optical and x-ray fields
Open this publication in new window or tab >>Molecular electronic,  vibrational and rotational motion in optical and x-ray fields
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The subject of this theoretical  study is the role ofelectronic structure as well as of rotational and vibrational motionson interactions between molecules and electromagnetic radiation,ranging from optical to x-ray. The thesis concerns both linear and nonlinear regimes of the light-matter interaction. The first part of the thesis is devoted to propagation of opticalpulses with different time-structure through various nonlinear absorbers.First we explain the double-exponential decay of fluorescence caused by photobleaching of pyrylium  salt irradiated by a train of short (100 fs) optical pulses. The main reason for this effect is the transversal inhomogeneity of the light beam which makes the dynamics of the photobleaching differ in the core of the pulse and on its periphery. We also explore the optical power limitingof C60 fullerene irradiated by either microsecond optical pulses or a picosecond pulse trains. Enhancement of nonlinear absorption is caused by strong triplet-triplet absorption that becomes important due toelongation of the interaction time.Here we show the importance of the repetitionrate for the optical power limiting performance.The second part of the thesis addresses the interaction of optical and x-rayfields with rotational degrees of freedom of molecules. In this part the main attention is paid to the rotational heating caused by the recoil, experienced by molecules due to the ejection of photoelectrons. We have quantitatively explained two qualitatively different experiments with the N2 molecule.We predict the interference modulation of the recoil-induced shift,which is a shift of the photoelectron line caused by the rotational recoil effect, as a function of the photon energy.The developed theory also explains the rotational heating ofmolecules observed in the optical fluorescence induced by x-ray radiation.Based on this explanation, we suggest a new scheme of the optical fluorescence induced by x-rays that allows to detect the recoil effect via the recoil-inducedsplitting of the optical resonance.The last part of the thesis focuses on multi-mode nuclear dynamics of the resonant Auger scattering from the C2H2 molecule, that was the subject of a recent experimental study.Here we develop a theory that explains the observed vibrationalscattering anisotropy. We have found that three qualitatively different mechanisms are responsible for this phenomenon. The first mechanism is the interference of the direct and resonance scattering channels. The second mechanismis the interference of the resonant scattering channels through core excitedstate with the orthogonal orientation of the vibrational modes of core excitedstate. The Young's double slit like interference of the quantum pathways through the double-well potential of the bending motion of core excited state is the third mechanism of the vibrational scattering anisotropy.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. viii, 67 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2009:24
Keyword
x-ray, nonlinear optics, photobleaching, recoil, anisotropy, Auger
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-11386 (URN)978-91-7415-483-2 (ISBN)
Public defence
2009-12-01, FB 53, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100713Available from: 2009-11-10 Created: 2009-11-03 Last updated: 2011-11-23Bibliographically approved

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Ågren, Hans

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