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Phase sensitive x-ray absorption driven by strong infrared fields
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO).ORCID iD: 0000-0003-1269-8760
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
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2005 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 71, no 4, 043407Article in journal (Refereed) Published
Abstract [en]

In this paper it is demonstrated that electron vibrational absorption of molecules driven by strong IR field provides rich physical interpretations of dynamical processes on a short time scale. The phase of an infrared field influences strongly the trajectory of the nuclear wave packet and the probing spectrum. It is shown that the probe spectrum keeps memory of the infrared phase even after that the pump field left the system. The phase effect takes maximum value when the duration of the probe pulse is of the order of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The phase effect is different for oriented and disordered molecules and depends strongly on the intensity of pump radiation. It can be an effective tool to study charge transfer processes like proton transfer in hydrogen bonded networks.

Place, publisher, year, edition, pages
2005. Vol. 71, no 4, 043407
Keyword [en]
synchrotron-radiation; laser; pulses; molecules
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5490DOI: 10.1103/PhysRevA.71.043407ISI: 000228752700085Scopus ID: 2-s2.0-26944469351OAI: oai:DiVA.org:kth-5490DiVA: diva2:9873
Note

QC 20100825

Available from: 2006-03-15 Created: 2006-03-15 Last updated: 2017-11-21Bibliographically approved
In thesis
1. Pulse Propagation in Nonlinear Media and Photonic Crystals
Open this publication in new window or tab >>Pulse Propagation in Nonlinear Media and Photonic Crystals
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

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

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

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

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

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 49 p.
Keyword
Photonic Crystals, Nonlinear optics, X-ray spectroscopy
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3886 (URN)91-7178-275-3 (ISBN)
Public defence
2006-03-31, FB42, AlbaNova, Roslagstullsbaken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100906Available from: 2006-03-15 Created: 2006-03-15 Last updated: 2011-11-23Bibliographically approved
2. X-ray Spectroscopy of Molecules Driven by Strong IR Fields
Open this publication in new window or tab >>X-ray Spectroscopy of Molecules Driven by Strong IR Fields
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The current thesis deals with one important branch of the physics of ultrafast processes, namely modeling of femtosecond nuclear dynamics. We suggest a new type of time resolved spectroscopy, the phase sensitive infrared-x-ray pump probe spectroscopy, which combines rich opportunities of IR laser techniques in quantum control of molecular systems with the site selectivity of x-rays. We have developed and applied a dynamical theory of x-ray pump-probe spectroscopy to study different molecular systems. Special attention is paid to design of the wave packets of desirable shape and spectral composition. Such a quantum control of the nuclear wave packet enables the study of molecular properties in regions that are unavailable by standard x-ray spectroscopies. The IR - x-ray pump probe spectroscopy is nicely suited to perform mapping of wave packet trajectories, to study revival phenomena, femtosecond chemical dynamics, and proton transfer, to mention a few examples.

Our simulations show that the phase of the infrared pulse strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. Such a dependence is caused by the transfer of the phase of the IR field to the wave packet through the interference of the one (x-ray) and two-photon (IR + x-ray) excitation channels. The time resolved x-ray spectra are sensitive to the shape, duration and delay time between the pulses. The phase of the IR pulse influences the molecular dynamics also when the Rabi period becomes comparable with the period of vibrations, breaking down the rotating wave approximation. We predict a phase memory effect which is a promising technique in studies of chemical dynamics on different time scales. It is shown that the final state interaction with the pump affects the probe spectrum when the pump and probe pulses overlap.

In a further step, we explore the electronic recoil effect in x-ray photoelectron spectroscopy, which has recently attracted attention of experimentalists due to its sensitivity to intramolecular interaction. We show that an IR field enhances the manifestation of the recoil effect through the formation of extensive vibrational wave packets. The theory of x-ray Raman scattering from molecules with strong spin-orbit coupling accompanied by electron-hole interaction is developed and applied to simulations of resonant x-ray Raman scattering of the HCl molecule. Special attention is paid to the theoretical methodologies to reduce the computational cost of our wave packet codes.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. ix, 53 p.
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3937 (URN)91-7178-277-X (ISBN)
Public defence
2006-05-19, Sal FR4, AlbaNova Universitetscentrum, Roglagstullsbacken 21, Stochholm, 10:00
Opponent
Supervisors
Note
QC 20100825Available from: 2006-05-05 Created: 2006-05-05 Last updated: 2011-11-23Bibliographically approved

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