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Electron-nuclear Dynamics in Nonlinear Optics and X-ray spectroscopy
KTH, School of Biotechnology (BIO).
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: urn:nbn:se:kth:diva-4339ISBN: 978-91-7178-634-0 (print)OAI: oai:DiVA.org:kth-4339DiVA: diva2:11872
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
List of papers
1. Dynamics of cavityless lasing generated by ultrafast multiphoton excitation
Open this publication in new window or tab >>Dynamics of cavityless lasing generated by ultrafast multiphoton excitation
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2006 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, no 3, 033814Article in journal (Refereed) Published
Abstract [en]

A dynamical theory is developed with the purpose of explaining recent experimental results on multiphoton-excited amplified stimulated emission (ASE). Several conspicuous features of this experiment are analyzed, like the threshold dependence of the spectral profile on the pump intensity, and spectral shifts of the ASE pulses co- and counterpropagating relative to the pump pulse. Two models are proposed and evaluated, one based on the isolated molecule and another which involves solvent interaction. The spectral shift between the forward and backward ASE pulses arises in the first model through the competition between the ASE transitions from the pumped vibrational levels and from the bottom of the excited-state well, while in the solvent-related model the dynamical solute-solvent interaction leads to a relaxed excited state, producing an additional ASE channel. In the latter model the additional redshifted ASE channel makes the dynamics of ASE essentially different from that in the molecular model because the formation of the relaxed state takes a longer time. The variation of the pump intensity influences strongly the relative intensities of the different ASE channels and, hence, the spectral shape of ASE in both models. The regime of ASE changes character when the pump intensity crosses a threshold value. Such a phase transition occurs when the ASE rate approaches the rate of vibrational relaxation or the rate of solute-solvent relaxation in the first excited state.

Keyword
Cavitation; Electric excitation; Laser applications; Mathematical models; Optical pumping; Photons; Solvents; Stimulated emission; Vibration control; Amplified stimulated emission (ASE); Multiphoton excitation; Solute-solvent relaxation; Vibrational relaxation; Ultrafast phenomena
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-6994 (URN)10.1103/PhysRevA.74.033814 (DOI)000241067100139 ()2-s2.0-33748950997 (Scopus ID)
Note

QC 20100813. Tidigare titel: Dynamics of cavityless lasing generated by ultra-fast multi-photon excitation. Titel ändrad 20100813.

Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
2. Self-sustained pulsation of amplified spontaneous emission of molecules in solution
Open this publication in new window or tab >>Self-sustained pulsation of amplified spontaneous emission of molecules in solution
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2006 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 2, 215-227 p.Article in journal (Refereed) Published
Abstract [en]

Temporal oscillations of amplified spontaneous emission of molecules are studied theoretically. From the proposed theory and numerical simulations, it is found that the self-pulsations originate in an interplay between stimulated emission and saturable absorption. A stability analysis demonstrates the crucial role of the photoabsorption in this process, which can be regulated by a proper choice of buffer molecules. Variations in the saturable absorption mediate a transition from damped oscillations to self-sustained pulsations. The role of propagation effects as well as of the interaction of co- and counter-propagating pulses is also investigated. Numerical simulations, demonstrating the theoretical findings, are performed for a model 3-level system and for an organic chromophore; 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4'-(6-hydroxyhexyl sulphonyl) stilbene.

Keyword
Computer simulation; Damping; Light absorption; Mathematical models; Molecular dynamics; Oscillations; Stimulated emission; Buffer molecules; Damped oscillations; Self-sustained pulsation; Stability analysis; Spontaneous emission
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-5488 (URN)10.1088/0953-4075/39/2/002 (DOI)000235457800005 ()2-s2.0-29144478864 (Scopus ID)
Note
QC 20100813Available from: 2006-03-15 Created: 2006-03-15 Last updated: 2017-11-21Bibliographically approved
3. Interplay of one-and two-step channels in electrovibrational two-photon absorption
Open this publication in new window or tab >>Interplay of one-and two-step channels in electrovibrational two-photon absorption
2005 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 109, no 42, 9507-9513 p.Article in journal (Refereed) Published
Abstract [en]

We present a theory of two-photon absorption that addresses the formation of spectral shapes taking the vibrational degrees of freedom into account. The theory is used to rationalize the observed differences between the spectral shapes of one- and two-photon absorption. We find that the main cause of these differences is that the two-step and coherent two-photon spectral bands are different even considering a single final state. Our formalism is applied to the N101 molecule (p-nitro-p'-diphenylamine stilbene), which was recently studied experimentally. Simulations show that the two-step two-photon electrovibrational absorption results in a blue shift of the absorption spectrum in agreement with the measurements.

Keyword
limiting properties, chromophores, spectra, excitation, media, Aromatic compounds; Computer simulation; Degrees of freedom (mechanics); Electron absorption; Molecular vibrations; Electrovibrational absorption; Spectral bands; Spectral shapes; Two-photon absorption
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-15140 (URN)10.1021/jp0536100 (DOI)000232857300018 ()2-s2.0-27744539913 (Scopus ID)
Note
QC 20100813Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
4. Many-photon dynamics of photobleaching
Open this publication in new window or tab >>Many-photon dynamics of photobleaching
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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.

Keyword
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:nbn:se:kth:diva-6997 (URN)10.1021/jp074756x (DOI)000251140700003 ()2-s2.0-36949023529 (Scopus ID)
Note
QC 20100713Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
5. Non-Adiabatic effects in Resonant Inelastic x-ray Scattering
Open this publication in new window or tab >>Non-Adiabatic effects in Resonant Inelastic x-ray Scattering
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2005 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 95, no 16, 163002- p.Article in journal (Refereed) Published
Abstract [en]

We have studied the spectral features of resonant inelastic x-ray scattering of condensed ethylene with vibrational selectivity both experimentally and theoretically. Purely vibrational spectral loss features and coupled electronic and vibrational losses are observed. The one-step theory for resonant soft x-ray scattering is applied, taking multiple vibrational modes and vibronic coupling into account. Our investigation of ethylene underlines that the assignment of spectral features observed in resonant inelastic x-ray scattering of polyatomic systems requires an explicit description of the coupled electronic and vibrational loss features.

Keyword
Nonadiabatic effects; Resonant inelastic X-ray scattering; Vibrational spectral loss; Energy dissipation; Ethylene; Resonance
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-6998 (URN)10.1103/PhysRevLett.95.163002 (DOI)000232558400019 ()2-s2.0-28844452203 (Scopus ID)
Note
QC 20100813Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
6. Dynamic interpretation of resonant x-ray Raman scattering: ethylene and benzene
Open this publication in new window or tab >>Dynamic interpretation of resonant x-ray Raman scattering: ethylene and benzene
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2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 3, 032505- p.Article in journal (Refereed) Published
Abstract [en]

We present a dynamic interpretation of resonant x-ray Raman scattering where vibrationally selective excitation into molecular resonances has been employed in comparison with excitation into higher lying continuum states for condensed ethylene and benzene as molecular model systems. In order to describe the purely vibrational spectral loss features and coupled electronic and vibrational losses the one-step theory for resonant soft x-ray scattering is applied, taking multiple vibrational modes and vibronic coupling into account. The scattering profile is found to be strongly excitation energy dependent and to reflect the intermediate states dynamics of the scattering process. In particular, the purely vibrational loss features allow one to map the electronic ground state potential energy surface in light of the excited state dynamics. Our study of ethylene and benzene underlines the necessity of an explicit description of the coupled electronic and vibrational loss features for the assignment of spectral features observed in resonant x-ray Raman scattering at polyatomic systems, which can be done in both a time independent and a time dependent picture. The possibility to probe ground state vibrational properties opens a perspective to future applications of this photon-in-photon-out spectroscopy.

Keyword
density-functional theory, core-hole localization, emission-spectroscopy, vibrational structure, surface adsorbates, symmetry-breaking, spectra, excitation, molecules, fluorescence
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-16983 (URN)10.1103/PhysRevA.76.032505 (DOI)000249786000076 ()2-s2.0-34548707080 (Scopus ID)
Note
QC 20100813Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
7. Multimode nuclear dynamics in resonant Auger scattering from acetylene
Open this publication in new window or tab >>Multimode nuclear dynamics in resonant Auger scattering from acetylene
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(English)Manuscript (Other academic)
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-7000 (URN)
Note
QC 20100813Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-08-13Bibliographically approved

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