| 1. |
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| 2. |
- Baev, A., et al.
(författare)
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Doppler interference in dissociative resonant photoemission
- 2002
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 66:2
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Tidskriftsartikel (refereegranskat)abstract
- Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.
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| 3. |
- Baev, A., et al.
(författare)
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Geometrical information on core-excited states obtained from interference quenching of vibrational states in resonant x-ray photoemission
- 2003
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 67:2
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Tidskriftsartikel (refereegranskat)abstract
- An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X (2)Sigma(g)(+) final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.
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| 4. |
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| 5. |
- Feifel, R., et al.
(författare)
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Interference quenching of nu('')=1 vibrational line in resonant photoemission of N-2 : A possibility to obtain geometrical information on the core-excited state
- 2002
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 89:10
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Tidskriftsartikel (refereegranskat)abstract
- An interference quenching of the nu=1 vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the nu=1 and nu=0 vibrational levels of the X(2)Sigma(g)(+) final state shows a surprising nonmonotonous variation as a function of frequency detuning, going through a minimum with a complete suppression of nu=1. We have developed a simple model which shows a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance R-c(0) of the core-excited state. A new way is thus established of determining the equilibrium bond distance for the core-excited state with a precision deltaR(c)(0)<10(-3) Angstrom.
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| 6. |
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| 7. |
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| 8. |
- Kitajima, M., et al.
(författare)
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Doppler effect in resonant photoemission from SF6 : Correlation between doppler profile and auger emission anisotropy
- 2003
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 91:21
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Tidskriftsartikel (refereegranskat)abstract
- Fragmentation of the SF6 molecule upon F 1s excitation has been studied by resonant photoemission. The F atomiclike Auger line exhibits the characteristic Doppler profile that depends on the direction of the photoelectron momentum relative to the polarization vector of the radiation as well as on the photon energy. The measured Doppler profiles are analyzed by the model simulation that takes account of the anisotropy of the Auger emission in the molecular frame. The Auger anisotropy extracted from the data decreases with an increase in the F-SF5 internuclear distance.
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| 9. |
- Naydenov, M, et al.
(författare)
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The Dynamics of miR-449a/c Expression during Uterine Cycles Are Associated with Endometrial Development
- 2023
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Ingår i: Biology. - : MDPI AG. - 2079-7737. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The human endometrium is a highly dynamic tissue. Increasing evidence has shown that microRNAs (miRs) play essential roles in human endometrium development. Our previous assay, based on small RNA-sequencing (sRNA-seq) indicated the complexity and dynamics of numerous sequence variants of miRs (isomiRs) that can act together to control genes of functional relevance to the receptive endometrium (RE). Here, we used a greater average depth of sRNA-seq to detect poorly expressed small RNAs. The sequencing data confirmed the up-regulation of miR-449c and uncovered other members of the miR-449 family up-regulated in RE—among them miR-449a, as well as several isoforms of both miR-449a and miR-449c, while the third family member, miR-449b, was not identified. Stem-looped RT-qPCR analysis of miR expression at four-time points of the endometrial cycle verified the increased expression of the miR-449a/c family members in RE, among which the 5′ isoform of miR-449c–miR-449c.1 was the most strongly up-regulated. Moreover, we found in a case study that the expression of miR-449c.1 and its precursor correlated with the histological assessment of the endometrial phase and patient age. We believe this study will promote the clinical investigation and application of the miR-449 family in the diagnosis and prognosis of human reproductive diseases.
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| 10. |
- Nikolova, M, et al.
(författare)
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Coupling miR/isomiR and mRNA Expression Signatures Unveils New Molecular Layers of Endometrial Receptivity
- 2021
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Ingår i: Life (Basel, Switzerland). - : MDPI AG. - 2075-1729. ; 11:12
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Tidskriftsartikel (refereegranskat)abstract
- Embryo implantation depends on endometrial receptivity (ER). To achieve ER, the preparation of the uterine lining requires controlled priming by ovarian hormones and the expression of numerous genes in the endometrial tissue. microRNAs (miRs) have emerged as critical genetic regulators of ER in fertility and of the diseases that are associated with infertility. With the rapid development of next-generation sequencing technologies, it has become clear that miR genes can produce canonical miRs and variants—isomiRs. Here, we describe miR/isomiR expression dynamics across the four time points of natural chorionic gonadotropin (hCG)-administered cycles. Sequencing of the small RNAs (sRNA-seq) revealed that the most significant expression changes during the transition from the pre-receptive to the receptive phase occurred in the isomiR families of miR-125a, miR-125b, miR-10a, miR-10b, miR-449c, miR-92a, miR-92b, and miR-99a. Pairing the analysis of the differentially expressed (DE) miRs/isomiRs and their predicted DE mRNA targets uncovered 280 negatively correlating pairs. In the receptive endometrium, the 5′3′-isomiRs of miR-449c, which were among the most highly up-regulated isomiRs, showed a negative correlation with their target, transcription factor (TF) MYCN, which was down-regulated. Joint analysis of the miR/isomiR and TF expression identified several regulatory interactions. Based on these data, a regulatory TF-miR/isomiR gene-target circuit including let7g-5p and miR-345; the isomiR families of miR-10a, miR-10b, miR-92a, and miR-449c; and MYCN and TWIST1 was proposed to play a key role in the establishment of ER. Our work uncovers the complexity and dynamics of the endometrial isomiRs that can act cooperatively with miRs to control the functionally important genes that are critical to ER. Further studies of miR/isomiR expression patterns that are paired with those of their target mRNAs may provide a more in-depth picture of the endometrial pathologies that are associated with implantation failure.
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| 11. |
- Baev, A., et al.
(författare)
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A quantum mechanical - Electrodynamical approach to nonlinear properties : Application to optical power limiting with platinum-organic compounds
- 2007
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Ingår i: Journal of nonlinear optical physics and materials. - 0218-8635. ; 16:2, s. 157-169
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Tidskriftsartikel (refereegranskat)abstract
- Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper the results of systematic studies of this problem for isotropic media. Our theoretical approach - the quantum mechanical-electrodynamical (QMED) approach - is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell's equations. This allows us to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation enables us to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime, it is often necessary to simultaneously account for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is highlighted here in a study of the optical power limiting with platinum-organic molecular compounds. © World Scientific Publishing Company.
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| 12. |
- 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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| 13. |
- Baev, A., et al.
(författare)
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General theory for pulse propagation in two-photon active media
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 117:13, s. 6214-6220
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of laser pulses of different lengths in nonlinear media of organic absorbers is described starting out from a recently suggested dynamical theory for two-photon absorption (TPA) of molecules in solutions [J. Opt. Soc. Am. B 19, 937 (2002)]. The roles of saturation effects and pulse duration on the suppression of TPA are emphasized. The numerical simulations of the pulse propagation are performed for a two-photon active charge transfer molecule using molecular parameters obtained from first principle calculations.
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| 14. |
- Baev, A., et al.
(författare)
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Light-matter interaction of strong laser pulses in the micro-, nano-, and picosecond regimes
- 2007
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Ingår i: Materials Research Society Symposium Proceedings. - 9781605604206 ; , s. 12-29
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Konferensbidrag (refereegranskat)abstract
- Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper results of systematic studies of this problem for isotropic media. Our theoretical approach-the quantum mechanical-electrodynamical (QMED) approach-is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell s equations. This allows to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation allows to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime it is often necessary to account simultaneously for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is here highlighted in a study of the optical power limiting with platinum-organic molecular compounds. © 2007 Materials Research Society.
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| 15. |
- Baev, A., et al.
(författare)
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Nonlinear propagation of strong multi-mode fields
- 2003
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 36, s. 3761-3774
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Tidskriftsartikel (refereegranskat)abstract
- We develop a strict theory of nonlinear propagation of few interacting stronglight beams. The key idea of our approach is a self-consistent solution ofthe nonlinear wave equation and the density matrix equations of the materialbeyond the rotatory wave approximation. We assume a Fourier expansion ofthe density matrixwhich goes beyond the conventionalTaylor expansions of thepolarization over the field amplitudeswhich is inadequate for the field strengthsthat we are interested in. Two qualitatively different situations are considered,with and without phase matching. Unlike in our previous paper (Baev et al2003 J. Opt. Soc. Am. B at press) devoted to the three-photon (TP) absorptioninduced upconverted lasing, we obtain here a strict solution for the nonlinearinteraction between different light beams. The general theory is applied to anumerical study of the role of saturation in TP photoabsorption by an organicchromophore in solution.
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| 16. |
- Baev, A, et al.
(författare)
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Picturing molecular femtosecond processes through an ultra-fast controllable X-ray shutter
- 2003
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 289, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- We show that frequency detuning in a resonant X-ray scattering experiment acts as an X-ray camera shutter by regulating the duration time of the scattering process. The camera shutter can be used to select processes at different time scales for observation. This is illustrated by a resonant Auger study of the ultra-fast dissociation of the core-excited HF molecule. We present experimental results and first principle simulations of the molecular fraction in the resonant Auger spectra of HF which is a dynamical parameter that well illustrates X-ray shutter controlled dissociation.
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| 17. |
- 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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| 18. |
- Feifel, R., et al.
(författare)
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Generalization of the duration-time concept for interpreting high-resolution resonant photoemission spectra
- 2004
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 69:2, s. 022707-
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Tidskriftsartikel (refereegranskat)abstract
- The duration-time concept, vastly successful for interpreting the frequency dependence of resonant radiative and nonradiative x-ray scattering spectra, is tested for fine-scale features that can be obtained with state of the art high-resolution spectroscopy. For that purpose resonant photoelectron (RPE) spectra of the first three outermost singly ionized valence states X (2)Sigma(g)(+), A (2)Pi(u), and B (2)Sigma(u)(+), are measured for selective excitations to different vibrational levels (up to n=13) of the N 1s-->pi(*) photoabsorption resonance in N-2 and for negative photon frequency detuning relative to the adiabatic 0-0 transition of this resonance. It is found that different parts of the RPE spectrum converge to the spectral profile of direct photoionization (fast scattering) for different detunings, and that the RPE profiles are asymmetrical as a function of frequency detuning. The observed asymmetry contradicts the picture based on the simplified notation of a common scattering duration time, but is shown to agree with the here elaborated concept of partial and mean duration times. Results of the measurements and the simulations show that the duration time of the scattering process varies for different final electronic and different final vibrational states. This owes to two physical reasons: one is the competition between the fast vertical and the slow resonant scattering channels and the other is the slowing down of the scattering process near the zeros of the real part of the scattering amplitude.
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| 19. |
- Feifel, Raimund, et al.
(författare)
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Generalization of the duration-time concept for interpreting state of the art high resolution resonant photoemission spectra
- 2004
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Ingår i: Physical Review A. ; 69
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Tidskriftsartikel (refereegranskat)abstract
- The duration-time concept, vastly successful for interpreting the frequency dependence of resonant radiative and nonradiative x-ray scattering spectra, is tested for fine-scale features that can be obtained with state of the art high-resolution spectroscopy. For that purpose resonant photoelectron (RPE) spectra of the first three outermost singly ionized valence states X 2Σg+, A 2Πu, and B 2Σu+, are measured for selective excitations to different vibrational levels (up to n=13) of the N 1s→π* photoabsorption resonance in N2 and for negative photon frequency detuning relative to the adiabatic 0-0 transition of this resonance. It is found that different parts of the RPE spectrum converge to the spectral profile of direct photoionization (fast scattering) for different detunings, and that the RPE profiles are asymmetrical as a function of frequency detuning. The observed asymmetry contradicts the picture based on the simplified notation of a common scattering duration time, but is shown to agree with the here elaborated concept of partial and mean duration times. Results of the measurements and the simulations show that the duration time of the scattering process varies for different final electronic and different final vibrational states. This owes to two physical reasons: one is the competition between the fast “vertical” and the slow “resonant” scattering channels and the other is the slowing down of the scattering process near the zeros of the real part of the scattering amplitude.
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| 20. |
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| 21. |
- Feifel, Raimund, et al.
(författare)
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Interference Quenching of v
- 2002
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Ingår i: Physical Review Letters. ; 89:10, s. 103002-1
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Tidskriftsartikel (refereegranskat)
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| 22. |
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| 23. |
- Feifel, R., et al.
(författare)
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Role of stray light in the formation of high-resolution resonant photoelectron spectra : an experimental and theoretical study of N-2
- 2004
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 134:1, s. 49-65
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Tidskriftsartikel (refereegranskat)abstract
- We show that the undular stray light, diffusely scattered by the optical system of a synchrotron beamline, can play an important role in the formation of high-resolution resonant photoelectron (RPE) spectra. The influence of the stray light is mediated through the Stokes doubling effect, with the Lorentzian tail of the spectral function being replaced by a more complicated form. This effect is shown to appear in the high-resolution resonant photoelectron spectrum of the N-2 molecule in which the spectral shape of the non-Raman (NR) bands differs qualitatively for the A(2)Pi(u) and X(2)Sigma(g)(+) final states. A particularly large enhancement of the non-Raman Stokes line is observed for the A-state while the picture is inverted for the X-state where the non-Raman band is suppressed. It is shown that the resonant photoemission profile is affected by two qualitatively different detunings, the detuning of the monochromatized line relative to the photoabsorption line and the detuning of the undulator harmonic relative to the same reference line. The experimental data show that the relative intensity of the non-Raman line strongly depends on the tuning of the undulator harmonic with respect to the selected monochromator bandpass, leading to a strong decrease of the Stokes line intensity for certain undulator detunings. A clear red-shift asymmetry for the decrease in the Stokes line intensity is observed when the monochromator line is detuned towards negative photon frequencies, whereas the picture is reverted for the situation of a positively detuned monochromator line. The results show the necessity to control the stray light and to investigate both the Raman and non-Raman contributions to the spectral profiles in order to avoid misinterpretation and in order to make full use of the information available in resonant photoemission spectra of molecules.
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| 24. |
- Gel'mukhanov, Faris, et al.
(författare)
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Dynamics of two-photon absorption by molecules and solutions
- 2002
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 19:5, s. 937-945
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Tidskriftsartikel (refereegranskat)abstract
- A dynamic density-matrix based theory of two-photon absorption (TPA) of molecules and solutions is presented. The theory highlights the influence of pulse duration, dephasing, and resonant conditions on the final TPA cross section as well as that of saturation, including a hierarchy of saturation intensities. A breakdown of the conventional identification of TPA with coherent one-step TPA is predicted for the long-pulse regime in which incoherent two-step TPA can even dominate the coherent one-step TPA process. The major role of the solvent is to enhance the off-resonant contributions to TPA furnished by collisional dephasing.
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| 25. |
- Gel'mukhanov, Faris, et al.
(författare)
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Resonant X-ray Raman scattering from dense gases and solutions
- 2001
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 346:06-maj, s. 437-442
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Tidskriftsartikel (refereegranskat)abstract
- To complement conventional theory of resonant X-ray Raman scattering (RXS) adapted either for rarefied gases or solids, we propose a theory and corresponding analysis for RXS from dense gases and solutions. We show that the dephasing broadening of the spectral lines due to interaction with buffer or solvent particles qualitatively changes the physics of the X-ray scattering. The dephasing results in an additional, two-step (TS) scattering, contribution to the RXS cross-section, which interferes with the Raman one-step (OS) channel and which shows a nondispersive behaviour, This results in a doubling of the spectral lines by detuning the excitation frequency away from resonance. The theory is demonstrated numerically for RXS of formaldehyde in solution.
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| 26. |
- Polyutov, Sergey, et al.
(författare)
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Self-sustained pulsation of amplified spontaneous emission of molecules in solution
- 2006
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:2, s. 215-227
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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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| 27. |
- Polyutov, Sergey, et al.
(författare)
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Spectral profiles of two-photon absorption : Coherent versus two-step two-photon absorption
- 2005
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Ingår i: Organic and Nanocomposite Optical Materials. - 1558997946 ; , s. 3-12
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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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| 28. |
- Reddy, I. V. A. K., et al.
(författare)
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Pulsed response theory prediction of ZnO nanocluster polarizabilities : A benchmark study
- 2021
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Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 778
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the interest in zinc oxide nanostructures and their properties, we calculate in this work molecular polarizabilities and hyperpolarizabilities of a series of zinc oxide nanoclusters using modern response theory in the form of damped and pulsed response for both Hartree-Fock and DFT reference states. We show that as the size of the cluster grows, both real and imaginary parts of polarizability, computed with these two distinct approaches, asymptotically converge. We also show the importance of eliminating the dangling bonds in small clusters for predicting the correct trend in the values of the HOMO/LUMO gap. Finally, we calculate the hyperpolarizability tensors, associated with the second order nonlinear optical effects, in the hexagonal (wurtzite) phase of ZnO nanoclusters and demonstrate a highly nonlinear growth of this quantity with the cluster size.
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| 29. |
- Salek, Pawel, et al.
(författare)
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Dynamical properties of X-ray Raman scattering
- 2003
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 5:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews theory for resonant X-ray scattering, emphasizing the dynamical aspects related to the nuclear motion during the scattering process. Various features of the theory are illustrated by simulations on small molecules in the gaseous phase. After the introduction de ning the X-ray Raman scattering process, we briefly describe some central concepts of its theory: the Raman law, the time hierarchy of X-ray scattering and the generalized Kramers-Heisenberg relation. We then go into some detail of various theoretical aspects of the process: transition moments and light polarization, time-dependent formulation and wave packets. We review two aspects of recent experimental focus: Doppler effects and generalized Franck-Condon factors. In the last part of the paper we discuss X-ray Raman scattering of dissociative core excited states, and the intriguing concept of a duration time for the scattering. We address dissociative resonant photoemission from first principles, with particular emphasis on the conditions for observing so-called atomic peaks and atomic holes. The atomic holes are the results of continuum continuum interference effects between the atomic and molecular channels which may act destructively under certain conditions. We demonstrate that the resonant contribution and the evolution of the atomic peaks can be subject to strong dynamical suppression caused by nuclear motion. In general, the molecular geometry dependence of the electronic transition moments can change the scattering cross section quite dramatically. This is exemplified here by an unusual spectral flattening for the B state of N-2, and by a breakdown of the spectator versus participator classification in a part of the non-radiative resonant photoemission spectrum of HF. The notion of a duration time in resonant X-ray scattering is put forward as a powerful concept for predicting and understanding qualitative aspects of many of the effects or processes treated in this paper. The role of the pulse shape for short pulse X-ray excitation is also discussed.
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| 30. |
- Salek, Pawel, et al.
(författare)
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Quantum chemical studies of three-photon absorption of some stilbenoid chromophores
- 2005
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:48, s. 11037-11042
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Tidskriftsartikel (refereegranskat)abstract
- Three-photon absorption of a series of donor-acceptor trans-stilbene derivatives is studied by means of density functional theory applied to the third-order response function and its residues. The results obtained by using different functionals are compared with experimental data for similar systems obtained from the literature. With a Coulomb attenuated, asymptotically corrected functional, the excitation energy to the first resonance state is much improved. Comparison with experiment indicates that this is the case for the three-photon cross section as well. In particular, the overestimation of the cross sections and underestimation of excitation energies offered by the density functional theory using common density functionals is corrected for. It is argued that a reliable theory for three-photon absorption in charge transfer and other chromophore systems thereby has been obtained. Further elaboration of the theory and its experimental comparison call for explicit inclusion of solvent polarization and pulse propagation effects.
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