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  • 1.
    Alvarez Ruiz, Jesus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Melero-Garcia, Emilio
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kivimäki, Antti
    Coreno, M.
    Erman, Peter
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Richter, R.
    Synchrotron radiation induced fluorescence spectroscopy of SF62005In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, p. 387-Article in journal (Refereed)
    Abstract [en]

    The fluorescence of gaseous SF6 was investigated after excitation with 25-80eV synchrotron radiation photons. The total UV-Vis-near IR fluorescence yield was recorded and interpreted in terms of inner valence excitations/ionizations and double excitations in SF6. Dispersed fluorescence measurements in the 400-1000 nm spectral range reveal excited S, S+, F and F+ fragments as solely responsible for the emission. The fluorescence intensity of some of the observed atomic transitions was monitored as a function of the excitation energy. Single, double and triple excitations as well as direct ionizations and shake-ups are proposed as the triggering processes responsible for the creation of the emitting fragments.

  • 2. Baev, A.
    et al.
    Gelmukhanov, Faris
    KTH, Superseded Departments, Chemistry.
    Kimberg, Viktor
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Nonlinear propagation of strong multi-mode fields2003In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 36, p. 3761-3774Article in journal (Refereed)
    Abstract [en]

    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.

  • 3. Burmeister, F.
    et al.
    Andersson, L. Mauritz
    Ohrwall, G.
    Richter, T.
    Zimmermann, P.
    Godehusen, K.
    Martins, M.
    Karlsson, H. O.
    Sorensen, S. L.
    Bjorneholm, O.
    Feifel, R.
    Wiesner, K.
    Goscinski, O.
    Karlsson, L.
    Svensson, S.
    Yencha, A. J.
    A study of the inner-valence ionization region in HCl and DCl2004In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 37, no 6, p. 1173-1183Article in journal (Refereed)
    Abstract [en]

    An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (similar to30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV.

  • 4. Ehlerding, A.
    et al.
    Viggiano, A. A.
    Hellberg, F.
    Thomas, R. D.
    Zhaunerchyk, V.
    Geppert, W. D.
    Montaigne, H.
    Kaminska, M.
    Österdahl, Fabian
    KTH, School of Engineering Sciences (SCI), Physics.
    af Ugglas, M.
    Larsson, M.
    Novotny, O.
    Mitchell, J. B. A.
    LeGarrec, J. L.
    Florescu-Mitchell, A. I.
    Rebrion-Rowe, C.
    Svendsen, A.
    El Ghazaly, M. A.
    Anderseng, L. H.
    The dissociative recombination of fluorocarbon ions III: CF2+ and CF3+2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 4, p. 805-812Article in journal (Refereed)
    Abstract [en]

    Cross sections and branching ratios are presented for the dissociative recombination of the CF2+ and C-3(+) ions with electrons. It is found that the channel producing CF + F is dominant for the reaction with CF2+ and the production of CF2 + F is dominant for the reaction with CF3+. The cross sections for these two ions are very similar.

  • 5. Fritioff, K
    et al.
    Sandstrom, J
    Andersson, P
    Hanstorp, D
    Hellberg, F
    Thomas, R
    Larsson, M
    Österdahl, Fabian
    KTH, Superseded Departments, Physics.
    Collins, G F
    Le Padellec, A
    Pegg, D J
    Gibson, N D
    Danared, H
    Kaillberg, A
    Observation of an excited C-4(2-) ion2004In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 37, no 11, p. 2241-2246Article in journal (Refereed)
    Abstract [en]

    This paper reports an experimental investigation of the electron impact detachment of C-4(-). We observe structure in the electron impact cross section for detaching a single electron from a C-4(-) cluster anion, which we attribute to the formation and decay of the C-4(2-) dianion. The system is energetically unstable and very rapidly decays via double autodetachment. The energy and width of the resonance were determined to be 8.8(5) eV and 1.4(5) eV, respectively, and the resonance lies 1.5(5) eV above the ground state of the neutral system. The experiment was conducted by merging monoenergetic electron and ion beams in the heavy ion storage ring CRYRING. The detachment channel was monitored by detecting neutral C-4 fragments.

  • 6.
    Gel'mukhanov, Faris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Plashkevych, O.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Anisotropic EXAFS measured in the Raman mode: a way to determine bond angles in randomly oriented species2001In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 34, no 5, p. 869-879Article in journal (Refereed)
    Abstract [en]

    It is shown that, contrary to the case of ordinary EXAFS measurements, EXAFS measured in the Raman mode is polarization sensitive for randomly oriented systems. This fact can be used to predict bond angles and gives an opportunity for a complete structural determination of gaseous or amorphous systems.

  • 7. Gharibi, Arash
    et al.
    Shen, Jian Qi
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Gu, Jing
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Tunable transient evolutional behaviours of a four-level atomic vapour and the application to photonic logic gates2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 5, p. 055502-Article in journal (Refereed)
    Abstract [en]

    The evolutional optical behaviours (turn-on dynamics) of a four-level N-configuration atomic system are considered based on the transient solution to the equations of motion of atomic probability amplitudes. It is shown that the quantum interference between the signal and control fields can lead to the controllable absorption and transparency properties of the atomic vapour. One of the most remarkable properties of the present scheme is that the absorption (or transmittance) of the probe light in the atomic vapour depends on the intensity ratio of the signal field to the control field, and thus the tunable optical features (transparency or opaqueness to the probe light) can be realized by tuning the quantum interferences between the signal and control fields. The present mechanism can be applicable to designs of some new photonic and quantum optical devices such as logic and functional devices as well as optical switches. Two typical photonic logic gates (NOT and NOR gates) designed based on the tunable four-level optical responses are presented as illustrative examples.

  • 8.
    He, Liming
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhu, Yunxia
    Zhang, Meng
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    A new relativistic Hartree-Fock calculation scheme and its application to the evaluation of fine-structure intervals for nd (n=3-40) series of sodium2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 22, p. 225007-Article in journal (Refereed)
    Abstract [en]

    We present a new second-order representation of the relativistic Hartree-Fock equation, which can be solved by the standard Hartree-Fock technique. An alternative reduction for the magnetic part of the Breit interaction is presented in an explicit expression. A corresponding program has been developed, which improves significantly the scaled linear mesh introduced by Herman and Skillman. The structures for a number of atoms and ions are calculated and the agreement of our results with those published is excellent. We evaluate the fine-structure intervals of nd(n = 3-40) Rydberg series for sodium. The inverted fine-structure splitting values are obtained directly as the differences of eigenvalues obtained from a self-consistent field procedure. Taking into account the Gaunt effect enables the accuracy of the calculation to be substantially improved. The complete treatments reproduce very well the inverted fine structures along the Rydberg series and the relative difference between the present results and the experiments does not exceed 4.4%.

  • 9.
    Hedqvist, Anders
    et al.
    KTH, Superseded Departments, Physics.
    O'Mullane, Martin
    Nordquist, Jonas
    KTH, Superseded Departments, Physics.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Zastrow, Klaus-Dieter
    JET Joint Undertaking, United Kingdom .
    Contributions of thermal charge exchange excitation to the Rydberg series of Cl16+2000In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 33, no 3, p. 375-382Article in journal (Refereed)
    Abstract [en]

    Spectra from the Rydberg series 1s-np for the principal quantum numbers n greater than or equal to 8 of Cl16+ are observed on the JET tokamak. Individual lines up to n = 15 are resolved. The line intensity of n = 10 is enhanced, relative to the underlying 1/n(3) scaling, due to charge exchange collisions with neutral deuterium in the ground state. The observations are compared with predictions based on available partial charge exchange cross section data. There is generally good agreement, however, some details of the predicted n-shell distribution are different from those observed in the experiment.

  • 10. Itala, E.
    et al.
    Huels, M. A.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kooser, K.
    Hagerth, T.
    Kukk, E.
    A comparative study of dissociation of thymidine molecules following valence or core photoionization2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 21, p. 215102-Article in journal (Refereed)
    Abstract [en]

    We have studied the fragmentation of gas phase thymidine following valence and core ionization using synchrotron radiation, combined with electron energy and ion mass resolved detection in coincidence. To identify certain fragment masses C-13 labelled thymidine was also used. We find that in large part, the photofragmentation of thymidine can be described as separated thymine and 2-deoxy-D-ribose cations. However, also the intact thymidine radical cation, formation of intact base and sugar cations from glycosidic bond cleavage and several new thymidine-specific fragments are observed after valence ionization. Conversely, at the photoionization of C 1s electrons neither parent thymidine cations nor any fragments above 55 amu were detected, and only ion pairs with small masses survive core ionization, Auger decay and the subsequent Coulomb separation of the DNA sub-unit. This demonstrates the genotoxic nature of soft x-rays which in cells induce complex clustered damage similar to those yielded by heavy particles.

  • 11.
    Jakubowska, Katarzyna
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Vall-llosera, Gemma
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kivimäki, Antti
    CNR-INFM, Laboratorio Nazionale TASC.
    Coreno, Marcello
    CNR-INFM, Laboratorio Nazionale TASC.
    Melero García, Emilio
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Stankiewicz, Marek
    Instytut Fizyki Im. Mariana Smoluchowskiego, Uniwersytet Jagielloński.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Lyman and Balmer emission following core excitations in methane and ammonia molecules2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, no 8, p. 1489-1500Article in journal (Refereed)
    Abstract [en]

    The intensities of hydrogen Lyman-alpha and Balmer series emission lines as a result of photoexcitation of free CH4 and NH3 molecules at the C 1s and N 1s edges have been measured. For methane, the total fluorescence yield in the visible region ( 300 - 650 nm) was also recorded. Excitation functions of the Balmer lines show relative intensity enhancement of Balmer-beta emission in comparison with Balmer-alpha at higher core- to- Rydberg excitations. The Lyman-alpha emission intensity, in general, follows the relations observed in the corresponding total ion yield measurements. Additionally, the Balmer-gamma and -delta yields were measured for ammonia molecules and they show intensity maxima at photon energies shifted closer to the N 1s threshold than Balmer-alpha and -beta. A quantum defect analysis is performed to find out which core excitations are responsible for this enhanced intensity. Dissociation pathways leading to the emission in H atoms are discussed.

  • 12.
    Kato, Takako
    et al.
    KTH, Superseded Departments, Physics. Natl. Institute for Fusion Science, Japan.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Hörling, Pontus
    KTH, Superseded Departments, Physics.
    Zastrow, Klaus Dieter
    KTH, Superseded Departments, Physics. JET Joint Undertaking, United Kingdom .
    Observations and modelling of line intensity ratios of OV multiplet line1996In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 29, no 18, p. 4241-4253Article in journal (Refereed)
    Abstract [en]

    Line intensity ratios of OV multiplet lines for the 2s3s(3)S(1)-2s3p(3)P(j) (J = 2,1,0) transitions are studied using a collisional radiative model and the results-are compared with measurements from the reversed field pinch experiments Extrap T1 and T2 at KTH. The measured line intensity ratios deviate from the predictions of the model and the possible causes for the discrepancy are discussed with regard to errors in rate coefficients and non-quasi-steady state.

  • 13. Kimberg, Victor
    et al.
    Zhang, S B
    Rohringer, Nina
    X-ray lasing in the CO molecule2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 16Article in journal (Refereed)
    Abstract [en]

    We theoretically demonstrate the feasibility of x-ray lasing in the CO molecule by the core ionization of the C K- and O K-shell by x-ray free-electron laser sources. Our numerical simulations are based on the solution of generalized Maxwell–Bloch equations, accounting for the electronic and nuclear degrees of freedom. The amplified x-ray emission pulses have an extremely narrow linewidth of about 0.1 eV and a pulse duration shorter than 30 fs. We compare x-ray lasing transitions to the three lowest electronic states of singly ionized CO. The dependence of the lasing efficiency on the spectral width of the x-ray fluorescence band, value and orientation of the electronic transition dipole moment, lifetime of the core-excited state and the duration of the pump pulse is analysed. Using a pre-aligned molecular ensemble substantially increases the amplified emission. Moreover, by controlling the molecular alignment and thereby the alignment of the transition dipole moment polarization, the control of the emitted x-ray radiation is achievable. Preparing the initial vibrational quantum state, the x-ray emission frequency can be tuned within the fluorescence band. The present scheme is applicable to other diatomic systems, thereby extending the spectral range of coherent x-ray radiation sources based on stimulated x-ray emission on bound transitions.

  • 14. Kivimaki, A.
    et al.
    Vall Llosera, Gemma
    Coreno, M.
    Huels, M. A.
    Stankiewicz, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Fluorescence emission at core-to-Rydberg excitations in the N-2 molecule2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 18Article in journal (Refereed)
    Abstract [en]

    Fluorescence emission at the N 1s edge of the N-2 molecule has been studied with synchrotron radiation excitation. The partial fluorescence yields in the ultraviolet (250-320 nm) and visible (300-650 nm) wavelengths were collected by scanning the photon energy across the core-to-Rydberg excitations and the N 1s ionization potential (IP). When compared to the total ion yield, both fluorescence yields are most enhanced at the excitations to high Rydberg orbitals. A discrete structure appears just below the N 1s IP only in the UV yield and is assigned to core-valence doubly excited states. Dispersed fluorescence spectra in selected wavelength windows were measured at several photon energies in order to find out which fragments are responsible for the enhancement of fluorescence emission just below the N 1s IP. The excitation functions determined and considerations on de-excitation pathways indicate that the main responsible is the N+ ion.

  • 15. Kivimaki, A.
    et al.
    Vall-Llosera, Gemma
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Coreno, M.
    Huels, M. A.
    Stankiewicz, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Line shape narrowing in the ultraviolet yield at the N 1s -> pi* resonance of the N-2 molecule2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 7Article in journal (Refereed)
    Abstract [en]

    The intensity of fluorescence emission in the wavelength region of 250-320 nm has been measured across the N 1s -> pi* resonance of the N-2 molecule. It displays a narrower line shape than the total ion yield recorded simultaneously. We explain the finding by the particularities of the resonant Auger transitions from the N 1s(-1) pi* state to the D-2 Pi(g) state in N-2(+) and by the subsequent D-2 Pi(g) -> A(2)Pi(u) emission.

  • 16.
    Kivimäki, Antti
    et al.
    KTH, Superseded Departments, Physics.
    Alvarez Ruiz, Jesus
    KTH, Superseded Departments, Physics.
    Erman, Peter
    KTH, Superseded Departments, Physics.
    Hatherly, Paul
    Melero Garcia, Emilio
    KTH, Superseded Departments, Physics.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Rius i Riu, Jaume
    KTH, Superseded Departments, Physics.
    Stankiewicz, Marek
    An energy resolved electron-ion coincidence study near the S 2p thresholds of the SF6 molecule2003In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 36, no 4, p. 781-791Article in journal (Refereed)
    Abstract [en]

    The fragmentation dynamics of the SF6 molecule following the excitations of S 2p electrons into unoccupied molecular orbitals has been studied using the energy-resolved electron-ion coincidence technique. Fragmentation patterns were found to depend on the particular excitation and on the electronic state of the molecular ion. The spectator resonant Auger decay at the 2p --> 6a(1g) resonance induces changes in the ion distributions as compared to direct photoionization. Furthermore, coincidence spectra related to the same Auger structure display different ion abundances at the 2t(2g) and 4e(g) shape resonances. Differences were also found in the Auger decay spectra. These findings give further support for the previously suggested many-electron character of the 4e(g) shape resonance.

  • 17. Kivimäki, Antti
    et al.
    Coreno, M.
    Richter, R.
    Alvarez Ruiz, Jesus
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Melero Garcia, Emilio
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    De Simone, M.
    Feyer, V.
    Vall Llosera, Gemma
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Prince, K. C
    Fluorescence emission following core excitations in the water molecule2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 5, p. 1101-1112Article in journal (Refereed)
    Abstract [en]

    Photon-induced fluorescence spectroscopy has been used to study the fragmentation of the water molecule at the O 1s is edge. Fluorescence emission has been observed from the neutral fragments H, O and OH as well as from the ionic fragments O+ and OH+. The extracted fluorescence yields of the H Lyman-alpha emission and O 2p(3)(S-4)3p(P-3) -> 2p(3)(S-4)3s(S-3) transitions show the same structures as the total ion yield spectrum but with different relative intensities. The most intense fluorescence emission is restricted to the region of the core excitations, while above the O 1s ionization limit the signal is much weaker (in the case of H) or below the detection limit (O, OH and OH+). The fluorescence emission is concluded to follow from the following general cascade: the core-excited states decay by resonant Auger transitions, the final states reached undergo dissociation into ionic and neutral fragments, and fluorescence occurs from excited fragments. In the case of the OH (A(2)Sigma(+) -> X-2 Pi) emission, the decay of core-excited states through soft x-ray emission may also be responsible for the observed fluorescence.

  • 18. Kukk, E.
    et al.
    Prumper, G.
    Sankari, R.
    Hoshino, M.
    Makochekanwa, C.
    Kitajima, M.
    Tanaka, H.
    Yoshida, H.
    Tamenori, Y.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Ueda, K.
    Electronic state dependence in the dissociation of core-ionized methane2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, no 18, p. 3677-3692Article in journal (Refereed)
    Abstract [en]

    Methane and deuteromethane molecules were core ionized using synchrotron radiation, and the ionic fragments from the molecular dissociation were detected in coincidence with the Auger electrons. The electron - ion coincidence spectra are analysed in terms of partial ion yields and ion kinetic energy distributions, both as functions of electron kinetic energy. The dependence of the fragmentation patterns on the electronic character of the Auger final states as well as on the excess energy available for dissociating the molecule is studied. The analysis reveals marked differences in the dissociation of the 2a(1)(-2) and 2a(1)(-1) 1t(2)(-1) states, interpreted as an `excess- energy- dependent' concerted dissociation process for the 2a(1)(-2) state and an ` electronic- state- dependent' sequential process for the 2a(1)(-1) 1t(2)(-1) state.

  • 19.
    Liu, Ji-Cai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Felicissimo, Viviane Costa
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Guimarães, Freddy Fernandes
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Wang, Chuankui
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Coherent control of population and pulse propagation beyond the rotating wave approximation2008In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 7, article id 074016Article in journal (Refereed)
    Abstract [en]

    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.

  • 20. Liu, X. J.
    et al.
    Cherepkov, N. A.
    Semenov, S. K.
    Kimberg, V.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Prumper, G.
    Lischke, T.
    Tanaka, T.
    Hoshino, M.
    Tanaka, H.
    Ueda, K.
    Young's double-slit experiment using core-level photoemission from N-2: revisiting Cohen-Fano's two-centre interference phenomenon2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 23, p. 4801-4817Article in journal (Refereed)
    Abstract [en]

    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.

  • 21. Maiorova, A. V.
    et al.
    Surzhykov, A.
    Tashenov, Stanislav
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Shabaev, V. M.
    Fritzsche, S.
    Plunien, G.
    Stöhlker, Th
    Polarization studies on the two-step radiative recombination of highly charged, heavy ions2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 12, p. 125003-Article in journal (Refereed)
    Abstract [en]

    Radiative recombination of a free electron into an excited state of a bare, high-Z ion is studied, together with its subsequent decay, within the framework of the density matrix theory and Dirac's relativistic equation. Special attention is paid to the polarization and angular correlations between the recombination and the decay photons. In order to perform a systematic analysis of these correlations the general expression for the double-differential recombination cross section is obtained by making use of the resonance approximation. Based on this expression, detailed computations for the linear polarization of x-ray photons emitted in the (e, 2 gamma) two-step recombination of uranium ions U92+ are carried out for a wide range of projectile energies.

  • 22.
    Melero Garcia, Emilio
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Alvarez Ruiz, Jesus
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabet
    KTH, School of Engineering Sciences (SCI), Physics.
    Erman, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kivimäki et al., Antti
    Fluorescence study of doubly excited states of molecular hydrogen2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 2, p. 205-213Article in journal (Refereed)
    Abstract [en]

    Photodissociation of molecular hydrogen has been investigated by means of fluorescence spectroscopy using synchrotron radiation. Balmer-alpha emission from atomic hydrogen photofragments was collected in the 20-55 eV excitation energy range. Experimental data are interpreted in terms of excitation and fragmentation of neutral doubly excited states and excited ionic states with the aid of recent theoretical model calculation.

  • 23.
    Miao, Quan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ding, Hong-Juan
    Sun, Yu-Ping
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Chuan-Kui
    Numerical analysis on optical limiting performance of a series of phthalocyanines for nanosecond pulses2012In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 45, no 8, p. 085402-Article in journal (Refereed)
    Abstract [en]

    The optical limiting properties of a series of peripherally substituted phthalocyanines with different central metals and axial chloride ligand for nanosecond pulses have been studied by solving numerically the two-dimensional paraxial field equation together with the rate equations using the Crank-Nicholson method. It is shown that all of these compounds exhibit good optical limiting behaviour, and phthalocyanines with heavier central metals have better optical limiting performance due to the faster intersystem crossing caused by the enhanced spin-orbit coupling. The major mechanism of optical limiting for long pulses is the sequential (singlet-singlet)x( triplet-triplet) nonlinear absorption. Dynamics of populations is characterized mainly by the effective transfer time of the population from the ground state to the lowest triplet state. The long lifetime of the triplet state is important but not determinant. In addition, the performance of optical limiting strongly depends on the thickness and concentration of the absorber.

  • 24. Murphy, N.
    et al.
    Niga, Petru
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. School of Physics, University College Dublin, Belfield, Dublin 4, Ireland.
    Cummings, A.
    Dunne, P.
    O'Sullivan, G.
    4d → 5p transitions in the EUV photoabsorption spectrum of Ba IV, Ba v and Ba VI2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 2, p. 365-373Article in journal (Refereed)
    Abstract [en]

    The photoabsorption spectra of Ba IV-Ba VI have been recorded using the dual laser plasma technique. Discrete structure due to 4d → 5p transitions has been observed in the 75-85 eV region and identified using Hartree-Fock with configuration interaction calculations. The excited states decay by autoionization involving ejection of 5s or 5p electrons and rates for the different processes and resulting linewidths were also calculated. From these calculations, synthetic spectra were produced and show excellent agreement with the experimental data.

  • 25. Novotny, O
    et al.
    Mitchell, J B A
    LeGarrec, J L
    Florescu-Mitchell, A I
    Rebrion-Rowe, C
    Svendsen, A
    El Ghazaly, M A
    Andersen, L H
    Ehlerding, A
    Viggiano, A A
    Hellberg, F
    Thomas, R D
    Zhaunerchyk, V
    Geppert, W D
    Montaigne, H
    Kaminska, M
    Österdahl, Fabian
    KTH, School of Engineering Sciences (SCI), Physics.
    Larsson, M
    The dissociative recombination of fluorocarbon ions: II. CF+2005In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, no 10, p. 1471-1482Article in journal (Refereed)
    Abstract [en]

    The dissociative recombination and excitation of CF+ have been measured at the ASTRID and CRYRING storage rings. Though examination of the available potential energy curves would suggest that the recombination rate would be large for this ion, in fact a rate constant of 5.2 +/- 1.0 x 10(-8) (T-e/300)(-0.8) cm(3) s(-1) was found. The recombination cross section at low energies falls off to a minimum at 0.5 eV centre-of-mass collision energy but exhibits resonances at energies above this. The dissociative excitation cross section leading to C+ + F was also measured and this displays an onset beginning at about 7 eV.

  • 26. Palmeri, P.
    et al.
    Quinet, P.
    Biemont, E.
    Gurell, J.
    Lundin, P.
    Norlin, Lars-Olov
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Royen, P.
    Blagoev, K.
    Mannervik, S.
    Lifetimes of metastable levels of singly ionized titanium: theory and experiment2008In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 12, p. 125703-Article in journal (Refereed)
    Abstract [en]

    This paper presents new theoretical lifetimes of metastable levels in singly ionized titanium, Ti II. Along with the lifetimes, transition probabilities for several decay channels from these metastable levels are presented. The calculations are supported by experimental lifetime determinations of the 3d(3) b D-2(5)/2 and 3d(2)(P-3)4s b P-2(3)/2 levels along with revised values of the previously published lifetimes of the 3d(2)(P-3)4s b P-4(5)/2 and 3d(2)(P-3)4s b P-2(1)/2 levels originating partly from a reanalysis utilizing a recently developed method applied on the previously recorded data and partly from new measurements. The presented theoretical investigation of lifetimes of metastable levels in Ti II shows that the HFR calculations are in general compatible with measurements performed using the ion storage ring CRYRING of Stockholm University. The transition probabilities of forbidden lines derived from the new lifetime values will be useful for the diagnostics of low density laboratory or astrophysical plasmas, particularly those encountered in the strontium filament found in the ejecta of eta Carinae.

  • 27. Piancastelli, M. N.
    et al.
    Fink, R. F.
    Feifel, R.
    Bassler, M.
    Sorensen, S. L.
    Miron, C.
    Wang, H.
    Hjelte, I.
    Bjorneholm, O.
    Ausmees, A.
    Svensson, S.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Bond-distance-dependent decay probability of the N 1s -> pi* core-excited state in N-22000In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 33, no 9, p. 1819-1826Article in journal (Refereed)
    Abstract [en]

    We report the observation of the unusually weak decay of the N 1s --> pi* core-excited N-2 molecule to the (B) over tilde (2)Sigma(u)(+) final state of N-2(+), which is only detectable in an experiment with high sensitivity. The resonant Auger spectra exhibit an unexpected dependence on the selected vibrational level of the intermediate state. Theoretical calculations show that the interference between direct and resonant photoemission as well as a strong geometry dependence of the decay probability on the bond distance give rise to the observed features.

  • 28.
    Pinheiro, Fernanda
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Department of Physics, Stockholm University, SE-106 91 Stockholm, Sweden .
    de Toledo Piza, A. F. R.
    Delocalization and superfluidity of ultracold bosonic atoms in a ring lattice2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 20, p. 205303-Article in journal (Refereed)
    Abstract [en]

    Properties of bosonic atoms in small systems with a periodic quasi-one-dimensional circular toroidal lattice potential subjected to rotation are examined by performing the exact diagonalization in a truncated many-body space. The expansion of the many-body Hamiltonian is considered in terms of the first-band Bloch functions, and no assumption regarding restriction to nearest neighbour hopping (tight-binding approximation) is involved. A finite size version of the zero temperature phase diagrams of Fisher et al (1989 Phys. Rev. B 40 546570) is obtained and the results, in remarkable quantitative correspondence with the results available for larger systems, discussed. Ground-state properties relating to superfluidity are examined in the context of two-fluid phenomenology. The basic tool, consisting of the intrinsic inertia associated with small rotation angular velocities in the lab frame, is used to obtain the ground state 'superfluid fractions' numerically. They are analytically associated with one-body, uniform solenoidal currents in the case of the adopted geometry. These currents are in general incoherent superpositions of contributions from each eigenstates of the associated reduced one-body densities, with the corresponding occupation numbers as weights. Full coherence occurs therefore only when only one eigenstate is occupied by all bosons. The obtained numerical values for the superfluid fractions remain small throughout the parameter region corresponding to the 'Mott insulator to superfluid' transition, and saturate at unity only as the lattice is completely smoothed out.

  • 29.
    Polyutov, Sergey
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Kimberg, Victor
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Baev, A.
    Institute for Lasers, Photonics and Biophotonics, State University of New York at Buffalo.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Self-sustained pulsation of amplified spontaneous emission of molecules in solution2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 2, p. 215-227Article in journal (Refereed)
    Abstract [en]

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

  • 30. Rice, J. E.
    et al.
    Reinke, M. L.
    Ashbourn, J. M. A.
    Ince-Cushman, A. C.
    Podpaly, Y. A.
    Gu, M. F.
    Bitter, M.
    Hill, K.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    The Ar(17+) Ly(alpha 2)/Ly(alpha 1) ratio in Alcator C-Mod tokamak plasmas2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 16, p. 165702-Article in journal (Refereed)
    Abstract [en]

    High-quality spectra of hydrogen-like Ar(17+) have been obtained from Alcator C-Mod tokamak plasmas using a spatially imaging high-resolution x-ray spectrometer system in an extensive study of the underlying high-n satellite lines. The ratio of Ly(alpha 2) (1S(1/2)-2P(1/2)) to Ly(alpha 1) (1S(1/2)-2P(3/2)) was found to be similar to 0.52 regardless of plasma parameters, which is somewhat greater than the ratio of the statistical weights of the upper n = 2 levels, 0.5. This difference is mainly due to the effects of collisional excitation of fine-structure sub-levels. For the observations presented here, electron densities were in an extended range from 3 x 10(19) to 4 x 10(20) m(-3) with electron and ion temperatures between 1 and 4 keV. Experimental results are compared to calculations from COLRAD, a collisional-radiative modelling code, and good agreement is shown.

  • 31. Royal, J
    et al.
    Larson, Åsa
    KTH, Superseded Departments, Physics.
    Orel, A E
    Effect of couplings in the resonance continuum2004In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 37, no 15, p. 3075-3083Article in journal (Refereed)
    Abstract [en]

    Electronic coupling of two or more resonances via the electron scattering continuum is investigated. The effect of this coupling as a function of the resonance curves and autoionization widths is investigated, and the conditions for the maximum effect are determined. The theory is applied to two physical problems, the product state distribution produced by the dissociative recombination of electrons with HeH+ and a one-dimensional model for ion-pair production resulting from electron collisions with H-3(+). It is found that the coupling does not affect the product state distribution in HeH+ but produces a significant effect in the H-3(+) model.

  • 32. Semenov, S. K.
    et al.
    Cherepkov, N. A.
    Matsumoto, M.
    Hatamoto, T.
    Liu, X. J.
    Prumper, G.
    Tanaka, T.
    Hoashino, M.
    Tanaka, H.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ueda, K.
    Interference modulation in the vibrationally resolved photoionization of the 1 sigma(g) and 1 sigma(u) core levels of the N-2 molecule2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 12, p. L261-L267Article in journal (Refereed)
    Abstract [en]

    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.

  • 33.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Beyond the Jaynes-Cummings model2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 22, p. 224013-Article in journal (Refereed)
    Abstract [en]

    The Jaynes-Cummings model is approached as a single-mode case of the solvable Lee model. This model can be treated for all mode numbers up to the continuum limit, which encompasses various adiabatic processes, finite renormalization and the emergence of irreversible time evolution.

  • 34.
    Sun, Yu-Ping
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Liu, Ji-Cai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    The propagation of a strong x-ray pulse followed by pulse slowdown and compression, amplified spontaneous emission and lasing without inversion2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 20Article in journal (Refereed)
    Abstract [en]

    We study self-seeded stimulated resonant x-ray Raman scattering and show a 20-fold compression of the strong XFEL pulse propagating through the resonant medium of atomic argon with the frequency (244.3 eV) tuned to the 2p(3/2)-4s resonance. The strong x-ray pulse inverts the medium and produces an extensive ringing tail which widens the power spectrum. Newly created seed field triggers the Stokes channel 3s-2p(3/2) of amplified spontaneous emission. The population inversions are quenched for longer propagation distances where lasing without inversion enhances the Stokes component. The pump pulse also generates weaker Stokes and anti-Stokes fields caused by four-wave mixing. The group velocity is decreased up to 78% of the speed of light in vacuum.

  • 35. Sun, Yu-Ping
    et al.
    Miao, Quan
    Zhou, Ai-Ping
    Liu, Rui-Jin
    Liu, Bo
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Institute of Nanotechnology, Spectroscopy and Quantum Chemistry, Siberian Federal University, 660041 Krasnoyarsk, Russia.
    Suppression of resonant auger effect with chirped x-ray free-electron laser pulse2018In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 51, no 3, article id 035602Article in journal (Refereed)
    Abstract [en]

    We study the Auger effect in the presence of strong x-ray free-electron lasers (XFELs) propagating through resonant argon vapors by solving the Maxwell-Bloch equations numerically. The simulations are based on the three-level system with the carrier frequency tuned in the 2p(3/2)-4s resonance. It is shown that the Auger branching is sensitive to the pulse area and duration. The relative Auger yield can be suppressed in the course of pulse propagation due to the interplay between the Auger decay and stimulated emission. Further suppression can be achieved by chirping the initial pulse, which is more effective for the long-pulse case. In addition, the sign and magnitude of the chirp rate play important roles in pulse reshaping and Auger emission.

  • 36.
    Sun, Yu-Ping
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Pietzsch, A.
    Hennies, F.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Karlsson, H. O.
    Schmitt, T.
    Strocov, V. N.
    Andersson, J.
    Kennedy, B.
    Schlappa, J.
    Foehlisch, A.
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rubensson, J-E
    Internal symmetry and selection rules in resonant inelastic soft x-ray scattering2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 16, p. 161002-Article in journal (Refereed)
    Abstract [en]

    Resonant inelastic soft x-ray scattering spectra excited at the dissociative 1 sigma(g) -> 3 sigma(u) resonance in gas-phase O(2) are presented and discussed in terms of state-of-the-art molecular theory. A new selection rule due to internal spin coupling is established, facilitating a deep analysis of the valence excited final states. Furthermore, it is found that a commonly accepted symmetry selection rule due to orbital parity breaks down, as the core hole and excited electron swap parity, thereby opening the symmetry forbidden 3 sigma(g) decay channel.

  • 37.
    Tidström, Jonas
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Ericsson, Marie
    Sjöqvist, Erik
    Andersson, L. Mauritz
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Open-system effects on slow light and electromagnetically induced transparency2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 13, p. 135501-Article in journal (Refereed)
    Abstract [en]

    The coherence properties of a three-level Lambda-system influenced by a Markovian environment are analysed. A coherence vector formalism is used and a vector form of the Lindblad equation is derived. Together with decay channels from the upper state, open-system channels acting on the subspace of the two lower states are investigated, i.e. depolarization, dephasing and amplitude damping channels. We derive an analytic expression for the coherence vector and the concomitant optical susceptibility, and analyse how the different channels influence the optical response. This response depends non-trivially on the type of open-system interaction present, and even gain can be obtained. We also present a geometrical visualization of the coherence vector as an aid to understand the system response.

  • 38. Urba, Laura
    et al.
    Lundh, Emil
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    One-dimensional extended Bose-Hubbard model with a confining potential: a DMRG analysis2006In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 24, p. 5187-5198Article in journal (Refereed)
    Abstract [en]

    The extended Bose-Hubbard model in a quadratic trap potential is studied using a finite-size density-matrix renormalization group method (DMRG). We compute the boson density profiles, the local compressibility and the hopping correlation functions. We observe the phase separation induced by the trap in all the quantities studied and conclude that the local density approximation is valid in the extended Bose-Hubbard model. From the plateaus obtained in the local compressibility it was possible to obtain the phase diagram of the homogeneous system which is in agreement with previous results.

  • 39.
    Vall-llosera, Gemma
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Álvarez Ruiz, Jesús
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Erman, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Melero García, Emilio
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Stankiewicz, Marek
    Instytut Fizyki, Jageillonian University.
    The npσ,π to EF emission systems in D2 studied by selective excitation2005In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, no 6, p. 659-664Article in journal (Refereed)
    Abstract [en]

    The np sigma 1 Sigma(u)(+) and np pi (1)Pi(u) states in D-2 have been selectively excited using monoenergetic synchrotron light in the range of 13.97-15.84 eV and the subsequent dispersed emission to the EF (1)Sigma(g)(+) state was observed using a grating spectrometer. In total, 18 emission bands from the levels n = 3-6 were studied and rotationally analysed. The intensities of the P and R branches relative to the Q branch were found to vary strongly in the np pi (1)Pi(u)(+)-EF(1)Sigma(g)(+) bands indicating the existence of predissociations of np pi (1)Pi(u)(+) levels above the dissociation limit D(1s) + D(2l).

  • 40.
    Velkov, Yasen
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Liu, Ji-Cai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Wang, Chuan-Kui
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    X-ray absorption of N2 accompanied by infrared-induced transitions between the ungerade and gerade core levels2008In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 14, p. 145601-Article in journal (Refereed)
    Abstract [en]

    We study a two-colour pump–probe scheme of x-ray absorption accompanied by core-hole hopping in the field of a strong IR laser. The process is exemplified for fixed-in-space and randomly oriented homonuclear diatomic molecules N2 near the 1σu → 1πg x-ray absorption transition. The laser field mixes the core holes of opposite parities and causes Rabi splitting of the core-excited states. The IR field results in spectral broadening and shifts of the x-ray resonances as well as decrease of x-ray photoabsorption. The Stark broadening of the x-ray absorption spectrum depends on the orientation of the molecule and the angle between the polarization vectors of the x-ray and IR fields. The spectral changes caused by the IR field are weaker for randomly oriented molecules in comparison with fixed-in-space molecules.

  • 41. Zhao, K.
    et al.
    Li, H. Y.
    Liu, J. C.
    Wang, C. K.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Dipolar effects on propagation of ultrashort laser pulse in one-dimensional para-nitroaniline (pNA) molecules2005In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, no 23, p. 4235-4245Article in journal (Refereed)
    Abstract [en]

    The dynamic behaviour of ultrashort (femtosecond) laser pulses in a molecular medium is studied by solving the full Maxwell-Bloch equations beyond the limits of the slowly varying envelope approximation and the rotating-wave approximation under the resonant and the non-resonant conditions. A one-dimensional asymmetric charge-transfer molecule, para-nitroaniline, is used as a model molecule whose electronic properties are calculated with the time-dependent hybrid density functional theory. Under the one-photon resonant condition, 4 pi pulse is separated into two sub-pulses. The weight of the second-harmonic component mainly contributed by the two-photon excitation becomes stronger with longer propagation time. Under the two-photon resonant condition, the separation of 4 pi pulse is not induced and many higher-order spectral components beyond the second-harmonic generation occur. Interestingly, when the pulse propagates for long enough, the carrier modification becomes so significant that a continuous spectrum is generated. The Fourier transform of the high-harmonic spectrum demonstrates that an even shorter laser pulse can be produced in both resonant and non-resonant propagations. The effects of permanent dipole moments on the pulse evolution are discussed.

  • 42.
    Zhao, Ke
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Liu, Ji-Cai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wang, Chuan-Kui
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Modulation of supercontinuum generation and formation of an attosecond pulse from a generalized two-level medium2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, p. 1523-1534Article in journal (Refereed)
    Abstract [en]

    The propagation of ultrashort pulses in a generalized two- level system, consisting of permanent dipole moments, is simulated by solving the full Maxwell - Bloch equations. Special attention has been paid to the supercontinuum generation of spectra and the formation of attosecond ( as) pulses. It is found that the supercontinuum generation is strongly modulated by both area and width of the pulse, resulting from the interference between the splitting pulses in the time domain and the implication of the time - energy uncertainty relation. The effect of the permanent dipole moment on the supercontinuum generation is discussed in detail. Calculations show that a well- shaped 132 as pulse can be generated from a 2 fs incoming pulse under the condition where the permanent dipole moment difference between two levels is equal to the transition dipole moment between them. Influences of carrier- envelope phase and time- dependent ionization on the spectral and temporal evolution of the ultrashort pulses are also discussed at length.

  • 43. Zhou, Yong
    et al.
    Miao, Quan
    Sun, Yuping
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wang, Chuan-Kui
    Solvent effect on dynamical TPA and optical limiting of BDMAS molecular media for nanosecond and femtosecond laser pulses2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 3, p. 035103-Article in journal (Refereed)
    Abstract [en]

    The dynamical two-photon absorption (TPA) cross section as well as optical limiting of a 4,4'-bis(dimethylamino) stilbene (BDMAS) molecular medium for the nanosecond and femtosecond laser pulses is studied. This molecular medium can be described by a cascade three-level model in the visible light regime. Our numerical results show that the BDMAS molecular medium exhibits a strong optical limiting behaviour. The saturation TPA in the femtosecond time domain can be observed, and materials with larger nonlinear absorption cross sections would be much easier to saturate. Due to the contribution of the two-step TPA, the dynamical TPA cross section of BDMAS for nanosecond pulses is about three orders of magnitude larger than that for ultrashort femtosecond pulses. Special attention has been paid to the solvent effects on the optimal limiting performance. With an enhancement of the polarity of solvents, the dynamical optical limiting window becomes broader. In the origin of optical limiting, the dynamical TPA cross section of BDMAS decreases when the polarity of solvents increases, which is in good agreement with the experiment.

  • 44.
    Álvarez Ruiz, Jesús
    et al.
    KTH, Superseded Departments, Physics.
    Erman, Peter
    KTH, Superseded Departments, Physics.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Rius Riu, Jaume
    KTH, Superseded Departments, Physics.
    Stankiewicz, Marek
    KTH, Superseded Departments, Physics.
    Veseth, V.
    Neutral dissociation of superexcited states in carbon monoxide2002In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 35, no 13, p. 2975-2983Article in journal (Refereed)
    Abstract [en]

    Neutral photodissociation of CO has been investigated using synchrotron light in the range 19-26 eV by observing dispersed fluorescence from excited neutral C atoms. Follow-up ab initio calculations support the observed neutral carbon excitation functions, which to a large extent are associated with the CO Rydberg - series converging to the CO+ C and D states.

1 - 44 of 44
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