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The paper considers novel behavior of molecule photodissociation probability under the influence of electromagnetic pulses in the femtosecond range. The study considers as examples the photodissociation of methane, ethylene and water molecules. The probability of photodissociation under radiation is calculated as a function of pulse duration for different values of the carrier frequency. In the limit of long pulses, the process probability, as expected, increases linearly with pulse duration. However, the dependence of photodissociation probability on pulse duration for the pulses in the femto- and sub-femtosecond ranges exhibits strong nonlinearity. The nonmonotonic effects occur at carrier pulse frequencies corresponding to the minimum values of the photodissociation cross-section. It is remarkable that the observed nonlinearity is described in the frame of the first order of perturbation theory for relatively small field amplitude and unrelated to the strong field effects. The proposed method of describing photodissociation is quite general and suitable for studying such processes under the influence of electromagnetic pulses of any duration.

At present, almost all areas of human activities involve the use of nanoparticles for solving various technical issues [1-6]...

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.

The paper investigates the cross-section and probability of absorption of ultrashort electromagnetic pulses by ITO nanoparticles in a dielectric matrix. It discusses the suitability of using the total probability of photoabsorption instead of the probability per unit time for such pulses. It is shown that in the case of negative detuning of the pulse carrier frequency from the plasmon resonance frequency, the photoabsorption probability is a nonlinear function of the pulse duration. For detuning with sufficiently large magnitude, the formation of a maximum is possible in this functional relationship, the position of which depends on the refractive index of the matrix. A method is proposed for measurement of environmental parameters by the analysis of time dependence of this photoprocess. Calculations are performed for a corrected Gaussian pulse and ITO nanoparticles with different doping levels.

International audience; The general properties of ultra-short electromagnetic pulse (USP) interactions with highly charge ions in dense and high temperature plasmas are considered. The application of USP in X-ray spectral range provided by modern technology including free-electron laser machines opens up new opportunities for investigations of dense plasmas. They are based on the possibility of USP penetration into optically dense media due to their broad spectral distribution. In the framework of the use of USP for active spectroscopy in high energy density plasmas, new expressions of the transition probabilities are proposed. An aluminum plasma at local thermodynamic equilibrium is considered. The interaction of USP with hydrogen-like ions at N e =2⋅10 22 cm-3 and T=1 keV is analyzed in details by taking into account both the specificity of the USP and the plasma effects, such as Stark and Doppler effects on the line profile of the excited radiative transitions. The results are applied for demonstration of optical depth and pulse duration effects on excitation probabilities of the n=1 to n=3 radiative transition, which is the simplest atomic scheme to observe fluorescence signal.

The IR photoabsorption cross section of a semiconductor nanoparticle has been calculated. Light is absorbed by conduction electrons and trapped electrons in the volume and surface of the nanoparticle. Electron concentrations have been obtained by minimizing the total free energy of charges in the system. The photoabsorption cross section has two characteristic maxima corresponding to the absorption by conduction electrons and by trapped electrons in the nanoparticle volume. The number of trapped electrons on the surface is relatively small, so that they do not contribute to the total cross section.

The frequency dependence of the cross section of photon absorption by semiconductor nanoparticles in the infrared range is considered. Light is absorbed by conduction electrons with plasmon formation and electrons in the traps both within the bulk and on the nanoparticle surface. The regularities of the photoabsorption cross section largely depend on the size of the nanoparticles. For sufficiently large nanoparticles, there appear only two characteristic peaks in the cross section distribution corresponding to light absorption by two types of electrons—conduction electrons and electrons in the volume traps of nanoparticles. The number of electrons trapped on the surface is relatively small, and the electrons do not contribute to the total cross section of photoabsorption. In the case of photon absorption by quantum dots, the contribution of these surface electrons as well as a third peak is evident. This result occurs due to a complex dependence of the number of electrons in the traps on their depth and s...

We present a theoretical study of the excitation of a charged quantum linear oscillator by chirped laser pulse with the use of probability of the process throughout the pulse action. We focus on the case of the excitation of the oscillator from the ground state without relaxation. Calculations were made for an arbitrary value of the electric field strength by utilizing the exact expression for the excitation probability. The dependence of the excitation probability on the pulse parameters was analyzed both numerically and by using analytical formulas.

An elementary quantum object, with which an electromagnetic field can interact, is a system consisting of two energy levels connected by a dipole-allowed transition.

Considerable advances have been made in the generation of ultrashort electromagnetic field pulses of controlled shape over a wide spectral range [1]. In the infrared, visible, and far-ultraviolet spectral regions, pulses have been produced with widths equal to the period of the electromagnetic field oscillation at the carrier frequency (single-cycle pulses).

Since polarization bremsstrahlung can be interpreted as scattering of virtual photons of a charged particle to a real photon by target electrons, PBs spectroscopy is in essence the generalization of ordinary spectroscopy and therefore has a number of features inherent in the latter. When the velocity of a charged particle approaches the velocity of light, this analogy becomes more exact since the electromagnetic field of a relativistic charge is close to the electromagnetic field of a real photon (a plane electromagnetic wave). One of manifestations of the said analogy is the Bragg condition for scattering of a virtual photon by crystal structures agreeing with the ordinary Bragg condition if it is considered that the wave vector of a virtual photon is directed along the velocity of an incident particle.

This chapter is dedicated to presentation of results of theoretical and experimental investigations of bremsstrahlung in scattering of nonrelativistic electrons with an energy of several tens of keV by solid-state targets carried out at the Collective Use Center of the Moscow Institute of Physics and Technology in 2009–2011.

Considered in this chapter are spectral, angular, polarization, and amplitude peculiarities of the near-resonance bremsstrahlung effect on ions with a core in strongly inelastic electron scattering that arise due to the presence of the polarization channel of the process and its interference with the static channel. This phenomenon plays an important role in processes of energy exchange between plasma and a near-resonance laser field as well as in experiments on triple interaction on electron and atomic beams and storage rings.

The quasi-classical theory of Bs on atoms and ions plays an important role in a number of applications such as radiation in partially ionized plasma, low-temperature plasma, gas discharge, absorption of radiation by plasma media, etc.

In Chap. 1 of this monograph the examples of calculation of PBs of an electron on a nanocluster in the low-frequency range were given, when the photon energy is from 1 to several tens of eV [1]. Here we will consider bremsstrahlung of a relativistic electron scattered on atomic clusters in a wide frequency range with an emphasis on the role of cooperative effects in the polarization and ordinary (static) channels of the process [2].

In this chapter with the use of the consistent quantum-electrodynamic approach the cross-section of bremsstrahlung of a fast charged particle on a one-electron and multielectron atom was obtained and analyzed within the framework of the first Born approximation.

In scattering of a fast ion in a medium, ordinary (static) bremsstrahlung caused by acceleration of an incident particle (IP) in the field of a target is suppressed because of the high mass of an ion. So the prevailing mechanisms of photon emission in this case are connected with excitation (real or virtual) of electronic degrees of freedom of colliding particles. In emission of high-energy photons with an energy of the order of the IP kinetic energy, when a momentum transferred in collision is great in comparison with the characteristic momenta of bound electrons, considered as main mechanisms of radiation, as a rule, are processes with changing state of an electron subsystem. Among these processes are radiation ionization, emission of secondary electrons, and radiation electron capture [1]. In the spectral region far from the kinematic limit, when the characteristic transferred momentum is not great, and the photon frequency is of the order of the frequencies of excitation of bound electrons of colliding particles, it is necessary to take into account radiation caused by virtual excitation of electronic degrees of freedom without change of an electronic state. This kind of radiation defined by the dynamic polarizability of a target and an IP was called polarization bremsstrahlung [2].

One of the first experiments for PBs on atoms was the work of the E.T. Verkhovtseva’s group [1], studied in which was the contribution of the “atomic” component of Bs to the spectrum of bremsstrahlung of electrons with the energy 600 eV scattered by xenon gas in a photon energy range of 70–150 eV. In this spectral range a “giant resonance” takes place in the xenon photoabsorption \( {\sigma_{ph }}\left( \omega \right) \), the said resonance being caused by the 4d-subshell of an atom, which according to the optical theorem $$ \operatorname{Im}\left\{ {\alpha \left( \omega \right)} \right\}=\frac{c}{{4\pi\omega }}{\sigma_{ph }}\left( \omega \right) $$

The cross-section of a photoprocess on an atomic ensemble (in case of a monatomic target) can be represented in the following form [1]: $$ d{\sigma_{{t\arg et}}}={{\left| {\sum\limits_j {\exp \left( {i\mathbf{q}{{\mathbf{r}}_j}} \right)} } \right|}^2}d{\sigma_{atom }}, $$

Polarization bremsstrahlung (PBs) is a fundamental radiative process arising in scattering of a charged particle by a target with internal degrees of freedom [1]. An elementary example of PBs is radiation of an electron on an atom. In this case internal degrees of freedom correspond to bound electrons of an atom that can reradiate an electromagnetic eigenfield of an incident particle (in this case of an electron). This process is presented in Fig. 1.1 together with ordinary bremsstrahlung (OBs) that is also called static bremsstrahlung (SBs).