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Dynamics of cavityless lasing generated by ultrafast multiphoton excitation
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).ORCID iD: 0000-0003-1269-8760
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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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.

Place, publisher, year, edition, pages
2006. Vol. 74, no 3, 033814
Keyword [en]
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: urn:nbn:se:kth:diva-6994DOI: 10.1103/PhysRevA.74.033814ISI: 000241067100139Scopus ID: 2-s2.0-33748950997OAI: oai:DiVA.org:kth-6994DiVA: diva2:11865
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
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. Pulse Propagation in Nonlinear Media and Photonic Crystals
Open this publication in new window or tab >>Pulse Propagation in Nonlinear Media and Photonic Crystals
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The present thesis is devoted to theoretical studies of pulse propagation of light through linear and nonlinear media, and of light-induced nuclear dynamics.

The first part of the thesis addresses propagation of light pulses in linear periodical media - photonic crystals. The main accent was put on studies of the angular properties of two qualitatively different types of photonic crystals: holographic photonic crystals, and impurity band based photonic crystals. The anisotropy of band structure, group velocity and pulse delay with respect to the light polarization are analyzed.

In the second part of the thesis a strict theory of nonlinear propagation of a few strong interacting light beams is presented. The key idea of this approach is a self-consistent solution of the nonlinear wave equation and the density matrix equations of the material. This technique is applied to studies of dynamics of cavityless lasing generated by ultra-fast multi-photon excitation. It is shown that interaction of co- and counter-propagating pulses of amplified spontaneous emission (ASE) affects the dynamics and efficiency of nonlinear conversion. Our dynamical theory allows to explain the asymmetric spectral properties of the forward and backward ASE pulses, which were observed in recent experiment with different dye molecules. It is shown that the ASE spectral profile changes drastically when the pump intensity approaches the threshold level. The effect of the temporal self-pulsation of ASE is studied in detail.

The third part of the thesis is devoted to light-induced nuclear dynamics. Time- and frequency-resolved X-ray spectroscopy of molecules driven by strong and coherent infrared (IR) pulses shows that the phase of the IR field strongly influences the trajectory of the nuclear wave packet, and hence, the X-ray spectrum. Such a dependence arises due to the interference of one (X-ray) and two-photon (X-ray + IR) excitation channels. The phase of the light influences the dynamics also when the Rabi frequency approaches the vibrational frequency, breaking down the rotating-wave approximation. The probe X-ray spectra are also sensitive to the delay time, the duration, and the shape of the pulses. The evolution of the nuclear wave packets in the dissociative core-excited state affects the dynamics of resonant Auger scattering from fixed-in-space molecules. One of the important dynamical effects is the atomic-like resonance which experiences electronic Doppler shift. We predict that the scattering of the Auger electrons by nearby atoms leads to new Doppler shifted resonances. These extra resonances show sharp maxima in the bond directions, which makes them very promising as probes for local molecular structure using energy and angular resolved electron-ion coincidence techniques. Our theory provides prediction of several new effects, but also results that are in good agreement with the available experimental data.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 49 p.
Keyword
Photonic Crystals, Nonlinear optics, X-ray spectroscopy
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3886 (URN)91-7178-275-3 (ISBN)
Public defence
2006-03-31, FB42, AlbaNova, Roslagstullsbaken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100906Available from: 2006-03-15 Created: 2006-03-15 Last updated: 2011-11-23Bibliographically approved

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