Dr. Rostyslav Danylo Profile

Dr. Rostyslav Danylo

at Laboratoire d'Optique Appliquée

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Publications (3)

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Proceedings Article | 9 March 2020 Presentation

Lasing without population inversion in singly ionized nitrogen molecules (Conference Presentation)

Rostyslav Danylo

Proceedings Volume 11270, 112700G (2020) https://doi.org/10.1117/12.2547363

KEYWORDS: Nitrogen, Molecules, Femtosecond phenomena, Terahertz radiation, Polarization, Picosecond phenomena

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Filamentation of femtosecond laser pulses at 800 nm provokes many spectacular phenomena like long range propagation, broadband THz generation, pulse self-compression, guided electric discharges and lasing effects. In particular, a coherent forward emission at 391 nm is observed that corresponds to a transition between levels B and X of the singly ionized Nitrogen molecule. Interpretation of this cavity-free air lasing is highly controversial. Several mechanisms like net electronic population inversion, rotational population inversion or Raman-like amplification were proposed but none of them is fully consistent and describes properly the gain properties. We have developed a model of lasing without population inversion in a V scheme arrangement. It is supported by experimental evidence for the long lasting coherent polarizations AX and BX required for such a V scheme. We show that the temporal shape of the lasing emission and its dependence with gas pressure can be well restituted theoretically. In addition, we present new supplementary measurements using consecutive twin femtosecond 800 nm pump pulses. A reduction of the global lasing signal at 391 by a factor ~ 1000 is observed when the gas is pumped with the twin pulses. This spectacular effect is observed over a range of delay between the twin pulses of several ps and can be interpreted in the frame of the V scheme.

Proceedings Article | 27 February 2015 Paper

Design of water molecule and its surrounding

R. Danylo, B. Okhrimenko, K. Yablochkova

Proceedings Volume 9371, 93712A (2015) https://doi.org/10.1117/12.2181938

KEYWORDS: Molecules, Hydrogen, Liquids, Chemical species, Electromagnetism, Absorption, Water, Matrices, Raman scattering, Process modeling

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Hydrogen bonds and their fluctuations are one of the factors that determine the unique properties of water [1]. Building models of formation and rupture of hydrogen bonds due to non-eigen vibrations of a molecule of water is to a large extent determined by the availability of accurate information on the geometric structure of the water molecule. Geometric parameters of the water molecule have been well studied for the gaseous state. This was aided by the possibility of an experimental study of the regularities in the rotational spectra of molecules. However, some questions about the geometry of the water molecule in the liquid state remain unanswered. For example, many sources state that the valence angle of the water molecule decreases during the transition into the liquid state [2]. Based on the experimental data of molecular vibration spectra in D₂O and H₂O molecules [3], the authors have estimated valence angle of water in the liquid state. Consequently, the value of the valence angle of water in liquid state was determined to be (89 ±2)°. A question of determination of libration vibrations of water molecule, as well as the analysis of its consequent inversion doubling, based on the new information on the equilibrium angle of the water molecules in the liquid state, constitutes an interest and is discussed in the present paper.

Proceedings Article | 7 December 2013 Paper

Spectroscopic modeling of water molecule

R. Danylo, B. Okhrimenko

Proceedings Volume 8923, 89235K (2013) https://doi.org/10.1117/12.2042802

KEYWORDS: Molecules, Liquids, Spectroscopy, Chemical species, Molecular spectroscopy, Oxygen, Hydrogen, Inverse problems, States of matter, Systems modeling

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This research is devoted to the vibrational spectroscopy inverse problem solution that gives a possibility to design a molecule and make conclusions about its geometry. The valence angle finding based on the usage of inverse spectral vibrational spectroscopy problem is a well-known task. 3N-matrix method was chosen to solve the proposed task. The usage of this method permits to make no assumptions about the molecule force field, besides it can be applied to molecules of matter in liquid state. Anharmonicity constants assessment is an important part of the valence angle finding. The reduction to zero vibrations is necessary because used matrix analytical expression were found in the harmonic approach. In order to find the single-valued inverse spectral problem of vibrational spectroscopy solution a shape parameter characterizing “mixing” of ω₁ and ω₂ vibrations forms must be found. The minimum of such a function Υ called a divergence parameter was found. This function characterizes method’s accuracy. The valence angle assessment was reduced to the divergence parameter minimization. The β value concerning divergence parameter minimum was interpreted as the desired valence angle. The proposed method was applied for water molecule in liquid state: β = (88,8 ±1,7)° . The found angle fits the water molecule nearest surrounding tetrahedral model including hydrogen bond curvature in the first approximation.

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