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Many-photon dynamics of photobleaching
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.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.ORCID iD: 0000-0003-2729-0290
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2007 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, 11961-11975 p.Article in journal (Refereed) Published
Abstract [en]

A detailed dynamical theory of photobleaching by periodical sequences of laser pulses is presented. The theory is used for interpretation of recent experiments with pyrylium salts. Our simulations are based on first-principles simulations of photoabsorption cross-sections and on empirical rate constants. Two competitive channels of photobleaching, namely, photobleaching from the lowest excited singlet and triplet states and from higher excited states, are found to explain different intensity dependences of the photobleaching rates in different samples. The process includes two-photon excitation from the ground state to the first or second excited singlet states and one-photon excitation from the first singlet or triplet states to higher excited states. The fluorescence follows double-exponential dynamics with two characteristic times. The first and the shorter one is the equilibrium settling time between the ground and the lowest triplet states. The second characteristic time, the time of photobleaching, is responsible for the long-term dynamics. The effective rate of photobleaching from the first excited singlet and lowest triplet states depends differently on the irradiance in comparison with the photobleaching in higher states. The first channel is characterized by a quadratic intensity dependence in contrast to the second channel that shows a cubic dependence. The competition between these photobleaching channels is very sensitive to the rate constants as well as to the repetition rate, the pulse duration, and the peak intensity. The double-exponential decay of the fluorescence is explained by the spatial inhomogeneity C of the light beam. The findings in this work are discussed in terms of the possibility of using many-photon-induced photobleaching for new three-dimensional read-write devices.

Place, publisher, year, edition, pages
2007. Vol. 111, 11961-11975 p.
Keyword [en]
DENSITY-FUNCTIONAL THEORY; MOLECULAR-ORBITAL METHODS; GAUSSIAN-TYPE BASIS; 2-PHOTON ABSORPTION; PHOTOPHYSICAL PROPERTIES; FLUORESCENCE MICROSCOPY; 2-STEP PHOTOLYSIS; ORGANIC-MOLECULES; TIME; EXCITATION
National Category
Industrial Biotechnology
Identifiers
URN: urn:nbn:se:kth:diva-6997DOI: 10.1021/jp074756xISI: 000251140700003Scopus ID: 2-s2.0-36949023529OAI: oai:DiVA.org:kth-6997DiVA: diva2:11868
Note
QC 20100713Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-12-06Bibliographically approved
In thesis
1. Electron-nuclear Dynamics in Nonlinear Optics and X-ray spectroscopy
Open this publication in new window or tab >>Electron-nuclear Dynamics in Nonlinear Optics and X-ray spectroscopy
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis is devoted to theoretical studies of the role of nuclear vibrations on nonlinear and linear absorption, pulse propagation, and resonant scattering of light. The molecular parameters needed for the simulations are obtained through suitable quantum chemical calculations, which are compared with available experimental data.

The first part of the thesis addresses to modeling of ampli ed spontaneous emission (ASE) in organic chromophores recently studied in a series of experiments. To explain the threshold behavior of the ASE spectra we invoke the idea of competition between di erent ASE channels and non-radiative quenching of the lasing levels. We show that the ASE spectrum changes drastically when the pump intensity approaches the threshold level, namely, when the ASE rate approaches the rate of vibrational relaxation or the rate of solute-solvent relaxation in the rst excited state. According to our simulations the ASE intensity experiences oscillations. Temporal self-pulsations of forward and backward propagating ASE pulses occur due to two reasons: i) the interaction of co- and counter-propagating ASE, and ii) the competition between the ampli ed spontaneous emission and o -resonant absorption.

In the second part of the thesis we explore two-photon absorption taking into account nuclear vibrational degrees of freedom. The theory, applied to the N101 molecule [p-nitro-p'- diphenylamine stilbene], shows that two-step absorption is red shifted relative to one-photon absorption spectrum in agreement with the measurements. The reason for this e ect is the one-photon absorption from the first excited state. Simulations show that two mechanisms are responsible for the population of this state, two-photon absorption and offresonant one-photon absorption by the wing of the spectral line.

In the third part of the thesis we study multi-photon dynamics of photobleaching by a periodical sequence of short laser pulses. It is found that the photobleaching as well as the uorescence follow double-exponential dynamics.

The fourth part of the thesis is devoted to the role of the nuclear dynamics in x-ray spectroscopy. Our studies show that the vibronic coupling of close lying core excited states strongly a ects the resonant x-ray Raman scattering from ethylene and benzene molecules. We demonstrate that the manifestation of the non-adiabatic e ects depends strongly on the detuning of photon energy from the top of photoabsorption. The electronic selection rules are shown to break down when the excitation energy is tuned in resonance with the symmetry breaking vibrational modes. Selection rules are then restored for large detuning. We obtained good agreement with experiment. Finally, our multi-mode theory is applied to simulations of the resonant Auger and x-ray absorption spectra of the ethyne molecule.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. iv, 70 p.
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:kth:diva-4339 (URN)978-91-7178-634-0 (ISBN)
Public defence
2007-05-04, FB 42, AlbaNova, Roslagstullsbacken, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100813Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-08-13Bibliographically approved
2. 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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