F. Gel’mukhanov

X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s-->sigma(*) resonance: Experiment and theory.

We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s-->sigma(*) excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.

Theory and first principles calculations of dissociative resonant photoionization: The evolution of atomic peaks and holes

We present theory and computational method for analyzing dissociative resonant photoemission from first principles. Particular emphasis is devoted to the conditions for observing so-called atomic p ...

Angular properties of band structures in one-dimensional holographic photonic crystals

One-dimensional photonic crystals with continuous distribution of the dielectric constant were fabricated by the use of photopolymer materials and laser holography. The angular dependence of light propagation through the system was studied experimentally and theoretically. It is shown that the Brewster angles for different bands are different, in contrast to the conventional two-layer Bragg reflector with a step-like distribution of the dielectric constant. Comparison of the theory with experimental data allowed us to define the parameters of the hologram—the dielectric contrast and the shrinkage of the structure.

Non-Linear Pulse Propagation in Many-Photon Active Isotropic Media

It is an experimental fact that 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 is based on numerical solutions of the density matrix and Maxwell’s equations and a quantum mechanical account of the complexity of the many-level electron-nuclear medium. This allows to accommodate a variety of non-linear 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 freedoms. We highlight the combination of quantum chemistry with classical pulse propagation which allows to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. It is shown that in the non-linear 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 non-linear propagation of a few interacting intense light pulses has been successfully applied to study, for example, frequency-upconversion cavity-less lasing in a chromophore solution, namely in an organic stilbenechromophore 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4′-(6-hydroxyhexyl sulphonyl) dissolved in dimethyl sulphoxide. Furthermore, the theory has been used to explain observed differences between spectral shapes of one- and two-photon absorption in the di-phenyl-amino-nitro-stilbene molecule. The present simulations evidence that the reason for this effect is the competition between two-step and coherent two-photon absorption processes