| 1. |
- Baev, A., et al.
(författare)
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Bi-directional description of amplified spontaneous emission induced by three-photon absorption
- 2005
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 22:2, s. 385-393
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Tidskriftsartikel (refereegranskat)abstract
- A semiclassical dynamic theory of the nonlinear propagation of a few interacting intense light pulses is applied to study the nonlinear counterpropagation of amplified spontaneous emission (ASE) induced by three-photon absorption of short intense laser pulses in a chromophore solution. Several important results from the modeling are reached for the ASE process developing in the regime of strong saturation. Accounting for ASE in both forward and backward directions with respect to the pump pulse results in a smaller efficiency of nonlinear conversion for the forward ASE compared with the case in which forward emission is considered alone, something that results from the partial repump of the absorbed energy to the backward ASE component; the overall efficiency is nevertheless higher than for the forward emission considered alone. The efficiency of nonlinear conversion of the pump energy to the counterpropagating ASE pulses is strongly dependent on the concentration of active molecules so that a particular combination of concentration versus cell length optimizes the conversion coefficient. Under certain specified conditions, the ASE effect is found to be oscillatory; the origin of oscillations is dynamical competition between stimulated emission and off-resonant absorption. This result can be considered one of the possible explanations of the temporal fluctuations of the forward ASE pulse [Nature 415, 767 (2002)].
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| 2. |
- Baev, A., et al.
(författare)
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Quantum-classical modeling of nonlinear pulse propagation in a dissolved two-photon active chromophore
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:11, s. 5379-5385
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we outline the implications of a quantum-classical approach for modeling two-photon absorption of organic chromophores in solution. The approach joins many-photon absorption dynamic simulations with quantum chemical first principles calculations of corresponding excitation energies and transition matrix elements. Among a number of conclusions of the study, we highlight three: (i) The use of either short- or long-pulse excitation is demonstrated to switch the absorptive capacity of the nonlinear medium owing to enhancement of the nonlinear stepwise processes; (ii) The two-photon cross section strongly depends on the way in which the dephasing rate decays when the laser frequency is tuned off-resonant with the corresponding molecular transition; (iii) The results of the pulse propagation simulations based on electronic structure data obtained with a new Coulomb attenuated functional is shown to be in much better agreement with the experimental results than those based on data received with traditional density functionals.
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| 3. |
- Carniato, S., et al.
(författare)
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K-L resonant X-ray Raman scattering as a tool for potential energy surface mapping
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 439:06-apr, s. 402-406
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Tidskriftsartikel (refereegranskat)abstract
- With help of theoretical calculations, we demonstrate that original pump-probe experiments, using IR laser as a pump and K-L X-ray Raman scattering as a probe, offer a powerful tool to map core-excited potential energy curves with very high energy resolution, beyond vibrational and lifetime limitations.
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| 4. |
- Costa Felicissimo, Viviane
(författare)
-
Infrared - X-ray pump probe spectroscopy
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis concerns theoretical studies of molecular interactions investigated by infrared and X-ray spectroscopic techniques, with emphasis on using the two technologies combined in pump probe experiments. Three main types of studies are addressed: the use of near-edge X-ray absorption fine structure spectra (NEXAFS) to manifest through-bond and through-space interactions; the role of hydrogen bonding on the formation of X-ray photoelectron spectra as evidenced by simulations of the water dimer; and the development of theory, with sample applications, for infrared X-ray pump probe spectroscopy - the main theme of the thesis. Ab initio calculations indicate that NEXAFS spectra give direct information about the through-bond and through-space interactions between vacant non-conjugated π* orbitals. It is found that the X-ray photoelectron spectrum of the water dimer differs strongly from the monomer spectrum in that two bands are observed, separated by the chemically shifted ionization potentials of the donor and the acceptor. The hydrogen bond is responsible for the anomalously strong broadening of these two bands. The studies show that X-ray core electron ionization of the water dimer driven by an infrared field is a proper technique to prove the proton transfered state contrary to conventional X-ray photoelectron spectroscopy. Our simulations of infrared X-ray pump-probe spectra were carried out using wave packet propagation techniques. The physical aspects of the proposed new X-ray spectroscopic method - phase sensitive Infrared - X-ray pump probe spectroscopy - are examined in detail in two sample applications - on the NO molecule and on the dynamics of proton transfer in core ionized water dimer. It is found that the phase of the infrared pump field strongly influences the trajectory of the nuclear wave packet on the ground state potential. This results in a phase dependence of the X-ray pump probe spectra. A proper choice of the delay time of the X-ray pulse allows to directly observe the X-ray transition in the proton transfered well of the core excited potential.
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| 5. |
- Feifel, R., et al.
(författare)
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X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance : Experiment and theory
- 2008
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:6
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Tidskriftsartikel (refereegranskat)abstract
- We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.
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| 6. |
- Felicissimo, Viviane, et al.
(författare)
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A theoretical study of the role of the hydrogen bond on core ionization of the water dimer
- 2005
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Ingår i: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 312:1-3, s. 311-318
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the interest in using X-ray spectra for probing of hydrogen bonded networks we developed a quantum model for simulations of the electronic-vibrational profile of the X-ray core photoelectron spectrum of the water dimer. It is found that the potential surfaces of the donor and acceptor O1s core-ionized states of this system display a qualitative difference. Large gradients of the potential in the core ionized state along some intermolecular coordinates combined with small vibrational frequencies breaks down completely the harmonic approximation. The band profiles are therefore treated using a quasi-continuum approximation. The weak hydrogen bonding and the drastic change of water dimer potential under core ionization is responsible for the anomalously strong vibrational broadening: 0.4 eV for the acceptor band and 0.6 eV for the donor band. The core ionization of the donor oxygen is accompanied by proton transfer which should be observable in X-ray fluorescence or Auger spectra.
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| 7. |
- Felicissimo, Viviane C., et al.
(författare)
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Enhancement of the recoil effect in x-ray photoelectron spectra of molecules driven by a strong ir field
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:2, s. 023414-
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Tidskriftsartikel (refereegranskat)abstract
- The C K and O K x-ray photoelectron spectra of the CO molecule, driven by a strong ir field, are studied theoretically. An enhancement of the recoil effect, which results in a strong dependence of the electron vibrational profile on the energy of x-ray photon, is found. The enhancement of the recoil effect happens due to an ir-induced increase of the wave-packet size. An extra enhancement occurs when the gradients of ground and ionized states approach each other. Under an increase of the photon energy, different sides of the x-ray photoelectron band experience blue- and redshifts, which are related to the difference of the gradients of the ground and core ionized states in the points of the vertical transitions near turning points of the wave packet. This makes the ir-x-ray pump-probe spectroscopy a very promising tool to study the shape of the potential energy surfaces.
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| 8. |
- Felicissimo, V.C., et al.
(författare)
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Probing weak molecular orbital interactions in non-conjugated diene molecules by means of near-edge X-ray absorption spectroscopy
- 2005
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:33, s. 7385-7395
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Tidskriftsartikel (refereegranskat)abstract
- Carbon and oxygen near-edge X-ray absorption fine structure (NEXAFS) spectra of 1,4-cyclohexadiene, p-benzoquinone, norbornadiene, norbornadienone, and cis-cis-[4,4,2]propella-3,8-diene-11,12-dione were calculated by means of Hartree-Fock and hybrid density functional theory using the static-exchange (STEX) approximation. The NEXAFS spectra are used as a probe to identify weak molecular interactions between the two non-conjugated ethylenic pi* orbitals present in these molecules. We show that the X-ray absorption spectrum of 1,4-cyclohexadiene exhibits some particular spectral structures in the discrete energy region that evidence diene through-bond orbital interaction, whereas absorption peaks are identified in the norbornadiene and norbornadienone spectra that indicate effective through-space orbital interactions. The molecular structure of the cis-cis-[4,4,2]propella-3,8-diene-11,12-dione isomer is such that the indirect through-bond or through-space diene orbital interactions are too weak to be assigned by its C1s NEXAFS spectrum.
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| 9. |
- Felicissimo, V.C., et al.
(författare)
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Proton transfer mediated by the vibronic coupling in oxygen core ionized states of glyoxalmonoxime studied by infrared-X-ray pump-probe spectroscopy.
- 2006
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 110:47, s. 12805-12813
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Tidskriftsartikel (refereegranskat)abstract
- The theory of IR-X-ray pump-probe spectroscopy beyond the Born-Oppenheimer approximation is developed and applied to the study of the dynamics of intramolecular proton transfer in glyoxalmonoxime leading to the formation of the tautomer 2-nitrosoethenol. Due to the IR pump pulses the molecule gains sufficient energy to promote a proton to a weakly bound well. A femtosecond X-ray pulse snapshots the wave packet route and, hence, the dynamics of the proton transfer. The glyoxalmonoxime molecule contains two chemically nonequivalent oxygen atoms that possess distinct roles in the hydrogen bond, a hydrogen donor and an acceptor. Core ionizations of these form two intersecting core-ionized states, the vibronic coupling between which along the OH stretching mode partially delocalizes the core hole, resulting in a hopping of the core hole from one site to another. This, in turn, affects the dynamics of the proton transfer in the core-ionized state. The quantum dynamical simulations of X-ray photoelectron spectra of glyoxalmonoxime driven by strong IR pulses demonstrate the general applicability of the technique for studies of intramolecular proton transfer in systems with vibronic coupling.
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| 10. |
- Felicissimo, Viviane C., et al.
(författare)
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The principles of infrared-x-ray pump-probe spectroscopy. Applications on proton transfer in core-ionized water dimers
- 2005
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 122:9
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we derive the basic physics underlying infrared-x-ray pump-probe spectroscopy (IR, infrared). Particular features of the spectroscopy are highlighted and discussed, such as dependence on phase of the infrared pulse, duration and delay time of the x-ray pulse, and molecular orientation. Numerical applications are carried out for the water dimer using wave packet techniques. It is shown that core ionization of the donor oxygen of the water dimer results in a drastic change of the potential with the global minimum placed in the proton transfer region. The results of the modeling indicate that IR-x-ray pump-probe spectroscopy can be used to study the dynamics of proton transfer in this core-ionized state, and that, contrary to conventional core level photoelectron spectroscopy, x-ray core-ionization driven by an IR field is a proper method to explore the proton transfer in a system like the water dimer. We observe that the trajectory of the nuclear wave packet in the ground state potential well is strongly affected by the absolute phase of the IR pulse.
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| 11. |
- Gavrilyuk, Sergey, et al.
(författare)
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Many-photon dynamics of photobleaching
- 2007
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 111, s. 11961-11975
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
- Gavrilyuk, Sergey, 1972-
(författare)
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Molecular electronic, vibrational and rotational motion in optical and x-ray fields
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 13. |
- Gavrilyuk, Sergey, et al.
(författare)
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Optical limiting for microsecond pulses
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:5
-
Tidskriftsartikel (refereegranskat)abstract
- We present a dynamical theory of nonlinear absorption and propagation of laser pulses with duration in the microsecond time domain. The general theory is applied to fullerene C-60 because of its good optical limiting properties, namely, a rather low ground state absorption and a strong triplet-triplet absorption. It is shown that sequential absorption involving strong triplet-triplet transitions is the major mechanism of nonlinear absorption. The intrinsic hierarchy of time scales makes an adiabatic solution of the coupled rate equations valid, which therefore can be reduced to a single dynamical equation for the ground state population. The slow evolution of this population is defined by an effective rate of population transfer to the triplet state and by the pulse duration. The propagation effect plays an important role in the optical power limiting performance. The intensity of the field as well as the population of the triplet state decreases during the pulse propagation, and a weakened nonlinear sequential two-photon absorption is followed by a linear one-photon absorption which gradually becomes the dominating process. The competition between these qualitatively different processes depends on the field intensity, the length of the absorber, and the concentration. The pulse propagation is studied by solving numerically the two-dimensional paraxial field equation together with the effective rate equation for the ground state population.
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| 14. |
- Gel'mukhanov, Faris, et al.
(författare)
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Young's double-slit experiment using two-center core-level photoemission : Photoelectron recoil effects
- 2007
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 156, s. 265-269
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Tidskriftsartikel (refereegranskat)abstract
- Core-level photoemission from N-2 can be considered an analogue of Young's double-slit experiment (YDSE) in which the double-slit is replaced by a pair of N 1s orbitals. The measured ratio between the 1 sigma(g) and 1 sigma(u) photoionization cross-sections oscillates as a function of photoelectron momentum, due to two-center YDSE interference, exhibiting a remarkable dependence on the vibrational sub-levels of the core ionized state. We theoretically demonstrate that the recoil of the photoelectron given to the ionized N atom strongly influences this interference pattern. The reason for this is that the momentum transfer affects the phases of the photoionization amplitudes.
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| 15. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
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Infrared–x-ray pump-probe spectroscopy of the NO molecule
- 2005
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:1
-
Tidskriftsartikel (refereegranskat)abstract
- Two color infrared-x-ray pump-probe spectroscopy of the NO molecule is studied theoretically and numerically in order to obtain a deeper insight of the underlying physics and of the potential of this suggested technology. From the theoretical investigation a number of conclusions could be drawn: It is found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. The trajectory experiences fast oscillations with the vibrational frequency with a modulation due to the anharmonicity of the potential. The dependences of the x-ray spectra on the delay time, the duration, and the shape of the pulses are studied in detail. It is shown that the x-ray spectrum keep memory about the infrared phase after the pump field left the system. This memory effect is sensitive to the time of switching-off the pump field and the Rabi frequency. The phase effect takes maximum value when the duration of the x-ray pulse is one-fourth of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The manifestation of the phase is different for oriented and disordered molecules and depends strongly on the intensity of the pump radiation.
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| 16. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
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Phase sensitive x-ray absorption driven by strong infrared fields
- 2005
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 71:4
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper it is demonstrated that electron vibrational absorption of molecules driven by strong IR field provides rich physical interpretations of dynamical processes on a short time scale. The phase of an infrared field influences strongly the trajectory of the nuclear wave packet and the probing spectrum. It is shown that the probe spectrum keeps memory of the infrared phase even after that the pump field left the system. The phase effect takes maximum value when the duration of the probe pulse is of the order of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The phase effect is different for oriented and disordered molecules and depends strongly on the intensity of pump radiation. It can be an effective tool to study charge transfer processes like proton transfer in hydrogen bonded networks.
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| 17. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
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Pump-probe spectroscopy of molecules driven by infrared field in both ground and excited electronic states
- 2006
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 125:20
-
Tidskriftsartikel (refereegranskat)abstract
- Pump-probe spectra of molecules driven by strong infrared (IR) field in both ground and excited states are studied theoretically. The role of the final state interaction becomes important when pump and probe pulses overlap, and the Rabi frequency is comparable with the lifetime broadening of the excited state and the duration of the pump pulse. Our theoretical approach is applied to x-ray absorption of nitrogen molecule and valence photoionization of carbon monoxide. It is shown that IR-x-ray pump-probe spectroscopy can directly evidence the delocalization of core hole.
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| 18. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
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Quantum wave packet revivals in IR plus X-ray pump-probe spectroscopy
- 2005
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Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 405:4-6, s. 398-403
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Tidskriftsartikel (refereegranskat)abstract
- The wave packet revivals constitute a central concept of X-ray spectroscopy with ultra-high spectral resolution. The revival phenomenon allows to resolve the anharmonical shift or rotational structure by means of time dependent measurements and makes X-ray pump-probe spectroscopy a powerful technique to study long-term dynamics of molecules in different phases. We study the revivals referring to the X-ray absorption spectrum of the NO molecule driven by strong infrared pulse. It is shown that the phase sensitive trajectories of the center of gravity of the wave packets and the X-ray spectra copy each other.
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| 19. |
- Guimaraes, Freddy Fernandes, 1975-
(författare)
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X-ray Spectroscopy of Molecules Driven by Strong IR Fields
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current thesis deals with one important branch of the physics of ultrafast processes, namely modeling of femtosecond nuclear dynamics. We suggest a new type of time resolved spectroscopy, the phase sensitive infrared-x-ray pump probe spectroscopy, which combines rich opportunities of IR laser techniques in quantum control of molecular systems with the site selectivity of x-rays. We have developed and applied a dynamical theory of x-ray pump-probe spectroscopy to study different molecular systems. Special attention is paid to design of the wave packets of desirable shape and spectral composition. Such a quantum control of the nuclear wave packet enables the study of molecular properties in regions that are unavailable by standard x-ray spectroscopies. The IR - x-ray pump probe spectroscopy is nicely suited to perform mapping of wave packet trajectories, to study revival phenomena, femtosecond chemical dynamics, and proton transfer, to mention a few examples. Our simulations show that the phase of the infrared pulse strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. Such a dependence is caused by the transfer of the phase of the IR field to the wave packet through the interference of the one (x-ray) and two-photon (IR + x-ray) excitation channels. The time resolved x-ray spectra are sensitive to the shape, duration and delay time between the pulses. The phase of the IR pulse influences the molecular dynamics also when the Rabi period becomes comparable with the period of vibrations, breaking down the rotating wave approximation. We predict a phase memory effect which is a promising technique in studies of chemical dynamics on different time scales. It is shown that the final state interaction with the pump affects the probe spectrum when the pump and probe pulses overlap. In a further step, we explore the electronic recoil effect in x-ray photoelectron spectroscopy, which has recently attracted attention of experimentalists due to its sensitivity to intramolecular interaction. We show that an IR field enhances the manifestation of the recoil effect through the formation of extensive vibrational wave packets. The theory of x-ray Raman scattering from molecules with strong spin-orbit coupling accompanied by electron-hole interaction is developed and applied to simulations of resonant x-ray Raman scattering of the HCl molecule. Special attention is paid to the theoretical methodologies to reduce the computational cost of our wave packet codes.
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| 20. |
- Hennies, F., et al.
(författare)
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Dynamic interpretation of resonant x-ray Raman scattering : ethylene and benzene
- 2007
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 76:3, s. 032505-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 21. |
- Hennies, F., et al.
(författare)
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Non-Adiabatic effects in Resonant Inelastic x-ray Scattering
- 2005
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 95:16, s. 163002-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Hikosaka, Y., et al.
(författare)
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X-ray absorption measured in the resonant Auger scattering mode
- 2008
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:7
-
Tidskriftsartikel (refereegranskat)abstract
- We report both experimental and theoretical studies on x-ray absorption measured in the resonant Auger scattering mode of gas phase carbon monoxide near the O1s -> 2 pi region. Both experiment and theory display a crucial difference between the x-ray absorption profiles obtained in the conventional and resonant scattering modes. Lifetime vibrational interference is the main source of the difference. It is demonstrated that such interference, which arises from a coherent excitation to overlapping intermediate levels, ruins the idea for obtaining x-ray absorption spectra in a lifetime broadening free regime.
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| 23. |
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| 24. |
- Kimberg, Victor, et al.
(författare)
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Angular anisotropy of the delay time of short pulses in impurity band based photonic crystals
- 2005
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Ingår i: Journal of Optics. A, Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 7:3, s. 118-122
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the transmission of short pulses through one-dimensional impurity band based photonic crystals. We found a strong dependence of the delay time on the angle of incidence. The delay time is larger for larger incident angles for the transverse electrical mode, while the delay time of the transverse magnetic mode has a qualitatively different angular dependence, especially in the region below the Brewster angle. The strong anisotropy of the delay time is traced to the anisotropy of the group velocity which is directly related to the angular dependence of the impurity band structure.
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| 25. |
- Kimberg, Victor, et al.
(författare)
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Dynamics of cavityless lasing generated by ultrafast multiphoton excitation
- 2006
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 74:3
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 26. |
- Kimberg, Victor, et al.
(författare)
-
Phase-sensitive wave-packet dynamics caused by a breakdown of the rotating-wave approximation
- 2006
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 73:2
-
Tidskriftsartikel (refereegranskat)abstract
- The water dimer driven by strong infrared field is studied in the two-vibrational mode approximation. A pump pulse excites the OH vibrational modes and creates a coherent superposition of vibrational states of the low-frequency OO mode. The solution of the Schrodinger equation in the adiabatic approximation shows a strong sensitivity of the OO vibrational wave-packet dynamics to the absolute phase of the pump field. This effect appears due to a break down of the rotating-wave approximation when the Rabi frequency of the OH vibrational transition approaches the frequency of the OH mode. The violation of the rotating wave approximation modifies considerably the interaction of the probe radiation with the laser-driven molecule.
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| 27. |
- Kimberg, Victor, 1973-
(författare)
-
Pulse Propagation in Nonlinear Media and Photonic Crystals
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 28. |
- Kimberg, Victor
(författare)
-
Pulse propagation in photonic crystals and nonlinear media
- 2005
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis is devoted to theoretical studies of light pulse propagation through different linear and nonlinear media. One dimensional holographic photonic crystals and one dimensional impurity band based photonic crystals are investigated as linear media. The effects of angular dependence of the band structures and pulse delay with respect to the light polarization are analyzed. A strict theory of nonlinear propagation of a few strong interacting light beams is presented and applied in the field of nonlinear optics. The key idea of this approach is a self-consistent solution of the nonlinear wave equation and the density matrix equations of the material beyond the so-called rotating wave approximation. The results of numerical studies led to a successful interpretation of recent experimental data [Nature, 415:767, 2002]. A theoretical study of the NO molecule by means of two-color infrared -- X-ray pump probe spectroscopy is presented. It was found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the X-ray spectrum. The dependence of the X-ray spectra on the delay time, the duration and the shape of the pulses are studied.
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| 29. |
- Kimberg, Victor, et al.
(författare)
-
Theoretical studies of angle-resolved ion yield spectra of core-to-valence transitions of acetylene
- 2009
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:11
-
Tidskriftsartikel (refereegranskat)abstract
- Recent experimental results on angle-resolved photoion-yield spectroscopy (ARPIS) spectra near the core-to-valence excitation in acetylene show significant anisotropies in the spectral profile measured at 0 degrees and 90 degrees regarding to the polarization direction of x-ray photons. In the present work, a theoretical model is proposed to simulate the fine structure and anisotropy in ARPIS. This employs two-dimensional potential energy surfaces of the ground and core-excited states, as well as transition dipole moments, including symmetric and antisymmetric bending modes to account for Duschinsky effect. The ARPIS is simulated by evaluation of the ion flux, which is found as a projection of the excited state wave packet on a particular direction in the molecular frame. Numerical simulations explain qualitatively the angular dependence of the experimental spectra of the 1s -> 1 pi(*)(g) and 1s -> 3 sigma(*)(u) transitions. The effects of the lifetime of the core-excited state, the direction of the ion flux, and the transition dipole moment are discussed.
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| 30. |
- Liu, Ji-Cai, et al.
(författare)
-
Coherent control of population and pulse propagation beyond the rotating wave approximation
- 2008
-
Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 41:7
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of populations of the vibrational states in a NO molecule ( one-photon absorption) and of the electronic states in a 4,4'-bis( dimethylamino) stilbene molecule ( two-photon absorption) is studied versus the frequency, intensity and shape of the laser pulse. We show that specially designed infrared laser pulses can build selective populations of certain vibrational states. A detuning of light frequency from the vibrational resonance qualitatively changes the dynamics of populations. It is found out that the populations of the nonresonant levels follow the pulse shape adiabatically if the detuning significantly exceeds the inverse characteristic time of the change of the pulse. Depopulation of the nonresonant vibrational states leads to a high population of the resonant state at the end of the pulse. Complete breakdown of the standard rotating wave approximation for a two-photon absorption process is observed even for a rather small intensity of the laser pulse. An analytical solution for the interaction of a pulse with a three-level system beyond the rotating wave approximation is obtained, and it is in close agreement with the strict numerical solution of the amplitude equations. Special attention is paid to the population dynamics of randomly oriented molecules. The orientational disorder as well as the vibrations limit the coherent population transfer. Calculations show the strong role of the anisotropy of photoexcitation in the coherent control of populations which can affect the anisotropy of photobleaching.
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| 31. |
- Liu, Ji-Cai, et al.
(författare)
-
Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse
- 2008
-
Ingår i: Chinese Physics B. - : IOP Publishing. - 1674-1056. ; 17:11, s. 4211-4217
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultras short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 40-bis(dimethylamino) stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.
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| 32. |
- Liu, Ji-Cai, et al.
(författare)
-
Dynamics of multilevel molecules and pulse propagation beyond rotating wave approximation near two-photon resonance
- 2007
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 76:4
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamics of multilevel molecules and pulse propagation is studied near the two-photon resonance. We have found a strict solution of this problem beyond the rotating wave approximation. Our analytical solution is in close agreement with the strict numerical solution for the 4,4(')-bis(dimethylamino) stilbene molecule. The compensation of the dynamical Stark shift is studied for fixed-in-space molecules. It is shown that the orientational disorder does not allow complete compensation of the dynamical Stark shift.
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| 33. |
- Liu, Ji-Cai, 1982-
(författare)
-
Dynamics of multiphoton processes in nonlinear optics and x-ray spectroscopy
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 34. |
- Liu, Ji-Cai, et al.
(författare)
-
Optical limiting of short laser pulses
- 2007
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 76:053804
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of pulse propagation accompanied by harmonic generation, stimulated Raman scattering, amplified spontaneous emission, and superfluorescence is studied near the two-photon resonance. We explore the optical limiting of intense and short laser pulses. The numerical solutions of the coupled Bloch and Maxwell's equations for the 4,4(')-bis(dimethylamino) stilbene molecule are compared with the two-photon area theorem. It is shown that the area theorem explains qualitatively the major dynamical properties of pulse propagation even if the propagation is accompanied by the generation of new fields. In agreement with the area theorem, we see that the conventional dependence of the transmittance on the propagation depth is not valid for intense pulses.
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| 35. |
- Liu, Ji-Cai, et al.
(författare)
-
Resonant inelastic X-ray Raman scattering induced by Rabi flopping of core holes
- 2008
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 453:1-3, s. 117-121
-
Tidskriftsartikel (refereegranskat)abstract
- A new scheme of X-ray pump-probe experiment is suggested in this Letter, namely resonant inelastic X-ray scattering accompanied by core-hole hopping induced by a strong laser field. In particular, we study the dynamics of X-ray Raman scattering of N-2 molecules in a strong IR field. The laser-induced mixing of the core holes of opposite parities opens symmetry forbidden scattering channels. The strength of the symmetry forbidden channels strongly depends on the interrelationship between the time of Rabi flopping of the core holes and the scattering duration or the duration of the X-ray pulse.
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| 36. |
- Liu, Ji-Cai, et al.
(författare)
-
Symmetry-forbidden x-ray Raman scattering induced by a strong infrared-laser field
- 2008
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 77:4, s. 043405-
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering accompanied by core-hole hopping induced by a strong infrared-laser field is studied for the nitrogen molecule. This process involves a strong laser-field-induced promotion of ungerade core holes created by a weak x-ray pulse to a gerade core level, which opens symmetry-forbidden scattering channels and gives rise to new features in the x-ray scattering spectrum. The core-hole hopping within the short lifetime of the core-excited state required for observation of the described process can be achieved at moderate intensities of the infrared field (similar to 10(12) W/cm(2)) because of the large transition dipole moment between the relevant core levels. The dynamics of resonant inelastic x-ray scattering assisted by change of core-hole parity is studied in detail versus the intensity, detuning, phase, and duration of the incident infrared-laser and x-ray pulses.
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| 37. |
- Liu, X. J., et al.
(författare)
-
Young's double-slit experiment using core-level photoemission from N-2 : revisiting Cohen-Fano's two-centre interference phenomenon
- 2006
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:23, s. 4801-4817
-
Tidskriftsartikel (refereegranskat)abstract
- The core-level photoelectron spectra of N-2 molecules are observed at high energy resolution, resolving the 1 sigma(g) and 1 sigma(u) components as well as the vibrational components in the extended energy region from the threshold up to 1 keV. The sigma(g)/sigma(u) cross section ratios display modulation as a function of photoelectron momentum due to the two-centre interference, analogous to the classical Young's double-slit experiment, as predicted by Cohen and Fano a long time ago. The Cohen-Fano interference modulations display different phases depending on the vibrational excitations in the core-ionized state. Extensive ab initio calculations have been performed within the Hartree-Fock and random phase approximations in prolate spheroidal coordinates. The dependence of photoionization amplitudes on the vibrational states was taken into account using the Born-Oppenheimer approximation. The ab initio results are in reasonable agreement with the experimental data. The theoretical analysis allows the modulation to be connected with the onset of transitions to the states of increasing orbital angular momentum which occurs at increasing photon energies. Deviation from the Cohen-Fano formula is found for both the experimental and the ab initio results and is attributed to electron scattering by the neighbouring atom. A new formula for the interference modulation is derived within the framework of the multiple scattering technique. It differs from the classical Cohen-Fano formula by the addition of twice the scattering phase of the photoelectron by the neighbouring atom. We demonstrate that one can measure directly the scattering phase by fitting our formula to the experimental results.
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| 38. |
- Liu, X. J., et al.
(författare)
-
Young's double-slit experiment using two-center core-level photoemission : Photoelectron scattering effects
- 2007
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 156, s. 73-77
-
Tidskriftsartikel (refereegranskat)abstract
- Core-level photoemission from N-2 can be considered as an analogue of Young's double-slit experiment (YDSE) in which the double-slit is replaced by a pair of N 1s orbitals. N 1s photoelectron spectra of N-2 are measured in the extended photon energy region up to similar to 1 keV at unprecedented resolution. The measured ratio between the 1 sigma(g) and 1 sigma(u) photoionization cross-sections oscillates as a function of electron momentum due to interference effects analogue to YDSE. We found a shift of the interference pattern with respect to a prediction by a simple model for coherent two-center emission, the Cohen-Fano formula, and attributed it to photoelectron scattering by the neighboring atom. We demonstrate that the shift can be used to determine the scattering phase of the photoelectron.
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| 39. |
- Minkov, Ivaylo, et al.
(författare)
-
Core-excitations of biphenyl
- 2005
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:7, s. 1330-1336
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution C(1s) near-edge X-ray absorption and X-ray photoionization spectra of the free biphenyl molecule are presented and theoretically analyzed in order to allow an assignment of the observed spectral features. Finite lifetime broadening, a high density of vibrational states, and a strong overlap of contributions from chemically different carbon atom sites only partially allow resolving the vibrational fine structure. However, the shape and width of the spectral profiles are strongly determined by both chemical shifts and vibronic effects. In particular, different from photoionization of valence levels, both types of core level spectra do not contain contributions from dihedral modes which are related to the twisting motion of the two phenyl rings. Contrary to naphthalene, C-H stretching modes are significantly enhanced in the core excitation spectra of biphenyl while the contributions from C-C stretching modes are reduced.
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| 40. |
- Minkov, Ivaylo, 1979-
(författare)
-
Nuclear Dynamics in X-ray Absorption and Raman Scattering
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents theoretical studies of several x-ray spectroscopies - x-ray absorption, x-ray photoelectron emission, radiative and non-radiative resonant Raman scattering spectroscopy. The main focus point is investigating the influence of nuclear dynamics on these spectra for a variety of small molecules - naphthalene, biphenyl, ethylene, the water dimer, HCl, CO. The theoretical tools used consist of the basic equations of the relevant x-ray spectroscopy. Wave packet methods are also used. The molecular parameters needed for our simulations are obtained through suitable quantum chemical calculations, based on either wave function or density functional methods. Our simulations are compared to experimental data, where available. Simulations of x-ray absorption and x-ray photoionization spectra for naphthalene and biphenyl show that the spectral shapes are heavily influenced by the joint effect of two factors -- chemical shifts and excitations of vibrational progression. Comparison between the two molecules and also comparison to a reference case -- benzene, provides useful insight into the molecular behavior under core excitation. In a further step, we consider the O1s x-ray photoelectron spectrum of the water dimer. A substantial broadening of the two bands originating from the donor and the acceptor oxygen is found. It is caused by excitations of soft intermolecular vibrational modes, associated with the hydrogen bond. Another strong influence of the nuclear dynamics is clearly seen in the resonant x-ray Raman scattering of HCl. Vibrational collapse is observed experimentally and confirmed theoretically for distinctive situations. This effect allows to eliminate completely the vibrational broadening, and hence, considerably increase the spectral resolution. We considered also the vibrational dynamics in resonant soft x-ray Raman scattering from ethylene. The importance of vibronic coupling and symmetry effects is discussed and emphasized. We obtained excellent agreement with the experimental data. We predict an interference effect in the resonant Auger scattering from fixed-in-space molecules. By exciting a molecule to a dissociative state and measuring the angular distribution of the Auger electrons in coincidence with the molecular ion, one can observe this effect. The interference pattern can be used after Fourier transformation for extracting structural data about the studied system. We have found that two-center interference leads to an enhancement of the recoil effect. Finally, it is shown that core excitation to doubly-excited dissociative Pi state is accompanied by Doppler splitting of the atomic peak in resonant Auger scattering from carbon monoxide.
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| 41. |
- Polyutov, Sergey, 1972-
(författare)
-
Electron-nuclear Dynamics in Nonlinear Optics and X-ray spectroscopy
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 42. |
- Polyutov, Sergey, et al.
(författare)
-
Interplay of one-and two-step channels in electrovibrational two-photon absorption
- 2005
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:42, s. 9507-9513
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 43. |
- Polyutov, Sergey, et al.
(författare)
-
Self-sustained pulsation of amplified spontaneous emission of molecules in solution
- 2006
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:2, s. 215-227
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 44. |
- Polyutov, Sergey, et al.
(författare)
-
Spectral profiles of two-photon absorption : Coherent versus two-step two-photon absorption
- 2005
-
Ingår i: Organic and Nanocomposite Optical Materials. - 1558997946 ; , s. 3-12
-
Konferensbidrag (refereegranskat)abstract
- We present a theory of two-photon absorption in solutions which addresses the, formation of spectral shapes taking account of the vibrational degrees of freedom. The theory is used to rationalize observed differences between spectral shapes of one- and two-photon absorption. We elaborate Oil two underlying causes. one trivial and one non-trivial, behind these differences. The first refers simply to the fact that the set of excited electronic states constituting the spectra, will have different relative cross sections for one- and two- photon absorption. The second reason is that the two-step and coherent two-photon absorption processes are competing, making the one- and two-photon spectral bands different even considering a, single final state. The theory is applied to the N-101 molecule [di-phenyl-amino-nitro-stilbene] which was recently studied experimentally in the paper.
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| 45. |
|
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| 46. |
|
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| 47. |
- Semenov, S. K., et al.
(författare)
-
Interference modulation in the vibrationally resolved photoionization of the 1 sigma(g) and 1 sigma(u) core levels of the N-2 molecule
- 2006
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:12, s. L261-L267
-
Tidskriftsartikel (refereegranskat)abstract
- The ratios of photoionization cross sections of the 1 sigma(g) and 1 sigma(u) shells of the N-2 molecule for the vibrational transitions to the nu' = 0 and nu' = 1 core-ionized states in the photon energy region between 440 and 550 eV have been measured. The calculations in the random phase approximation well reproduce the experimental data. The variation of the ratio with photon energy is attributed to the interference modulation that is caused by coherent photoemission from the two atoms, as an analogue of the Young's double-slit experiment. The calculations extended up to 1.8 keV allow connecting the modulation with the onset of transitions to the states of increasing orbital angular momentum which occurs at increasing photon energies and demonstrate that the main contribution to these modulations comes from the alpha continuum states.
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| 48. |
- Simon, M., et al.
(författare)
-
Elastic peak of K shell excited HCl molecule : Comparison HCl-DCl - Experiment and theory
- 2007
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 155:1-3, s. 91-94
-
Tidskriftsartikel (refereegranskat)abstract
- Fermosecond dynamics has been recently observed by resonant X-ray Raman scattering (RXRS) after excitation along the dissociative Cl 1s -> 6 sigma* resonance of gas phase HCl. In this paper, we show a method to take into account and correct for self-absorption of the elastic peak, in order to allow for quantitative comparison with theory. We have performed measurements on the DCl molecule exhibiting ultrafast nuclear motion. A comparison between HCl and DCl is presented.
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| 49. |
- Simon, M., et al.
(författare)
-
Femtosecond nuclear motion of HCl probed by resonant x-ray Raman scattering in the Cl 1s region
- 2006
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 73:2, s. 020706(R)-
-
Tidskriftsartikel (refereegranskat)abstract
- Femtosecond dynamics are observed by resonant x-ray Raman scattering (RXS) after excitation along the dissociative Cl 1s -> 6 sigma(*) resonance of gas-phase HCl. The short core-hole lifetime results in a complete breakdown of the common nondispersive behavior of soft-x-ray transitions between parallel potentials. We evidence a general phenomenon of RXS in the hard-x-ray region: a complete quenching of vibrational broadening. This opens up a unique opportunity for superhigh resolution x-ray spectroscopy beyond vibrational and lifetime limitations.
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| 50. |
- Sorensen, S. L., et al.
(författare)
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Electronic Doppler effect in resonant Auger decay of CO molecules upon excitation near a shake-up Pi resonance
- 2007
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : APS. - 1050-2947 .- 1094-1622. ; 76:062704
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Tidskriftsartikel (refereegranskat)abstract
- Wepresent an experimental observation of the electronic Doppler effect inresonant Auger spectra upon core excitation slightly above the carbonK edge of the CO molecule. Thus the electronic Dopplereffect has been identified in above-threshold excitation, and in atransition of symmetry. Ab initio calculations of the potentialenergy curves of the relevant states of CO and thewave packet technique have been employed to provide a theoreticalbackground to the experimental studies. The weak feature around 299.4 eVin the photoabsorption spectrum, whose decay has been investigated bythe present experiment, is assigned to double (core-valence) excitations toC 1s shake-up states |1s1−1*2 with a strong dissociative character,and the Doppler splitting of the atomic peak has beenreproduced by the simulation.
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