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International audience; The theory of photoionization describing the interaction of x-ray free-electron laser (XFEL) pulses and high-harmonic-generated (HHG) radiation is generalized to ultrashort laser pulses, where the concept of the standard ionization probability per unit time in Fermi’s golden rule and in Einstein’s theory breaks down. Numerical calculations carried out in terms of a generalized photoionization probability for the total duration of pulses in the near-threshold regime demonstrate essentially nonlinear behavior, while absolute values may change by orders of magnitude for typical XFEL and HHG pulses. XFEL self-amplified spontaneous emission pulses are analyzed to reveal general features of photoionization for random and regular spikes: the dependences of the nonlinear photoionization probability on carrier frequency and spike duration are very similar, allowing an analytical expectation value approach that is valid even when there is only limited knowledge of random and regular parameters. Numerical simulations carried out for typical parameters demonstrate excellent agreement.

In the work, the comparison of sensitivities of optical plasmon sensors constructed on the basis of semiconductor nanoparticles of various shapes is presented. The calculation was made within the framework of the dipole approximation. A characteristic of sensitivity is the value of the shift of the plasmon resonance maximum per unit change in the refractive index of a medium. The influence of the material of a nanoparticle and its shape on the sensitivity of an optical plasmon sensor is shown.

We investigated theoretically the time dependence of ultra-short laser pulse scattering by an atom at the high-frequency limit for the spectral and total probability of the process using new expression which we derived in this paper. We established that the time dependence of spectral scattering is presented by the curve with the maximum for sufficiently large detuning of scattering frequency from the carrier frequency of the pulse, while the total scattering probability is always the monotonically increasing function of time. We also studied the dependence of scattering probability on pulse duration at the long-time limit. It was shown that, at the long-pulse limit, the scattering probability is a linear function of pulse duration, while in the opposite case, it is a function with maximum. The position of this maximum is determined by the detuning of the scattering frequency from the carrier frequency of the pulse.

A series of previously undescribed N-aryl-N′-pyridin-2-ylureas were prepared via the reaction of 2-aminopyridines with benzoyl azides and tested in vitro as activators of glucokinase. Statistically significant reductions of glucose levels as compared with controls were demonstrated for several compounds.

The radiation absorption cross section of indium–tin oxide (ITO) semiconductor nanoparticles of various sizes placed in various media is calculated in the region of plasmon resonance. The photoabsorption cross sections calculated within the framework of the Mie theory and in the dipole approximation are compared with each other and with the available experimental data. The limits of applicability of the dipole approximation are determined. The prospects of using these nanoparticles as an active material in optical plasmon sensors are assessed.

International audience; On the basis of equations obtained in the framework of second-order quantum-mechanical perturbation theory, the standard approach to the calculation of scattering radiation probability is extended to the case of ultrashort laser pulses. We investigate the mechanism of the appearance of plasmon peaks in the spectrum of the plasma form factor for different parameters of the problem. For the case in which scattering on plasmons dominates over scattering on electron density fluctuations caused by chaotic thermal motion, we derive analytical expressions describing the scattering probability of ultrashort laser pulses on plasmons. Together with this, we obtain a simple expression connecting the frequency of scattered radiation and the energy transmitted from the incident pulse to plasmon, and vice versa. In considering the scattering probability, our emphasis is on the dependence on the pulse duration. We assess in detail the trends of this dependence for various relations between pulse carrier frequency and plasmon energy.

The process of scattering of radiation by indium‒tin oxide (ITO) nanoparticles is theoretically studied at various degrees of doping and for different radii of nanoparticles. Qualitative conclusions are made about the character of the dependence of the scattering cross section on the frequency with variation of the particle size and the percentage content of tin. The prospects of using ITO nanoparticles as an active substance in optical sensors are estimated.

In the work, the physico-mathematical model of an optical plasmon sensor constructed on the basis of semiconductor ellipsoidal nanoparticles is proposed. It is shown that the sensitivity of such a sensor is proportional to the value of the ellipsoid semiaxis along which polarization of acting radiation is directed.

International audience

The standard approach to calculate the Thomson scattering probability is reconsidered for the case of ultrashort incident laser pulses (USLPs). We established a new model for the interaction of USLP with plasmas that is based on Fermi's equivalent photon conception to calculate the spectral-angular differential Thomson scattering probability. The simulations demonstrate that the scattering probability for USLP is a non-monotonic function of pulse duration in contrast to the standard long-pulse model showing linear dependence. An analytical approach is developed to study the nonlinear behavior of the scattering probability as a function of pulse duration and other parameters.

The paper presents the general scheme of operation and the physico-mathematical model of an optical plasmon sensor based on indium-tin oxide (ITO) nanoparticles. The principle of operation of the "ITONPsensor" program intended for simulation of a response of the optical plasmon sensor to a change in parameters of a medium being measured is also described. The program was developed on the basis of the physico-mathematical model of absorption of radiation by semiconductor ITO nanoparticles.

We study the excitation dynamics of Fano resonance within the classical model framework of two linear coupled oscillators. An exact solution for the model with a damped harmonic force is obtained. The details of growth a Fano profile under the harmonic excitation is shown. For incident ultra-wideband pulse, the reaction of a system becomes universal and coincides with the time-dependent response function. The results of numerical calculations clarify two alternative ways for experimental measurement of the complete characteristics of a system: direct observation of the system response to a monochromatic force by frequency scanning or recording of time-dependent response to the delta-pulse. As a specific example, time-dependent excitation in a system consisting of a quantum dot and a metal nanoparticle is calculated. Then it is shown the applicability of the extended model of damped oscillators with radiative correction to describe the build-up a plasmon Fano resonance in a scattering of a femtosecond laser pulse by nanoantenna., 17 pages, 9 figures, 46 References