Manipulating electromagnetic radiation with magnetic photonic crystals

We examine manipulating electromagnetic waves in magnetic photonic crystals (MPCs) with external magnetic fields. We predict new giant magnetoreflectivity and giant magnetorefractivity effects: with an external magnetic field of a magnitude much smaller than the anisotropy field of the ferromagnet, the MPC can be changed from completely reflecting to nonreflecting with corresponding changes in the angle of refraction. Application to the storage of electromagnetic radiation is also discussed.     

Interactions of coherent electromagnetic radiation with nuclei

When coherent electromagnetic radiation resonantly couples two levels of a nucleus, the system can emit photons by stimulated and by spontaneous emission. The spontaneous emission spectrum is defined as the Fourier transform of the first-order correlation function of the magnetic or electric field operator. This function can be expressed in terms of one-time and two-time averages of nuclear operators. The one-time averages can be calculated by solving the Bloch-type equations for the matrix elements of the nuclear density operator. Application of the quantum regression theorem permits to calculate two-time averages with the aid of one-time averages and hence the radiated spectrum.     

Radiative ionization in slow ion-atom collisions

Bremsstrahlung from the ionization of inner shell electrons in slow ion atom collisions is considered. The yield predicted by the binary encounter approximation is small compared with experiment in 12–33 MeV O + Zr and O + Au collisions.     

Electron capture processes in ion-atom collisions

The development of the theory of electron capture processes in ion-atom collisions is reviewed in the present work. The formal theory of scattering is used to obtain the Born and the distorted wave Born series for the rearrangement scattering matrix. On the basis of these series, the applications of the first and second Born approximation, the OBK approximation, the DWBA and the Padé approximants to electron capture processes are discussed. The impulse approximation, the Faddeev method and the second order potential method are also explained. The results of the investigations of the high energy behaviour of the charge transfer cross section based on the Faddeev-Watson multiple scattering expansion are analysed.The methods of molecular and atomic eigenfunction expansions are presented and their relative merits discussed. The semi-classical treatment for determining the differential electron capture probability is reviewed. Results obtained in works utilising expansions in Sturmian, Gaussian and pseudo-state wave functions are also presented. An integral equation approach to the close coupling approximation is described. The field theoretic approach to investigate the electron capture process is discussed in the last section.The results obtained by different theoretical methods are compared with available experimental results.     

Electron capture in high-energy ion-atom collisions

We discuss the non-relativistic theory of electron capture from atoms (or ions) by ions when the relative velocity of the collision is greater than the orbital velocity of the captured electron. We emphasize the specific difficulties due to the two-body Coulomb potentials occurring in this process We show how the simplifications introduced by the small value of the electron to proton mass ratio can be used to provide a valuable tool to evaluate the adequacy of the existing theories. Extensive comparisons between theory and experiment are carried out and a number of new theoretical results are presented.     

Ultrahigh harmonics from laser-assisted ion-atom collisions

We present a theoretical analysis of high-order harmonic generation from ion-atom collisions in the presence of linearly polarized intense laser pulses. Photons with frequencies significantly higher than in standard atomic high-harmonic generation are emitted. These harmonics are due to two different mechanisms: (i) collisional electron capture and subsequent laser-driven transfer of an electron between projectile and target atom; (ii) reflection of a laser-driven electron from the projectile leading to recombination at the parent atom.     

X-ray productions in symmetric heavy ion-atom collisions

X-ray measurements for 50–200 keV impact Ne⁺ → Ne, Ar⁺ → Ar and Kr⁺ → Kr show an increase of a factor of 10 in the flourescence yield for Ar-L₂₃, a similar increase may occur for Kr-M₂₃, but for Ne-K the yield does not vary much.     

Absorption of resonant electromagnetic radiation in electron-atom collisions

Nonrelativistic quantum theory is used to study the possibility of amplification of electromagnetic radiation in forced braking scattering of an electron beam on atoms. The interaction of the atom with the electromagnetic field is considered in the resonant approximation. Cases of large and small detuning from resonance are considered. It is shown that for any orientation of the electron beam relative to the field polarization vector, absorption of radiation occurs, with the major contribution being produced by atomic electrons.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 79–84, April, 1986.The authors are indebted to M. F. Fedorov and S. I. Yakovlenko for their valuable discussion and advice.     

Positron lines from subcritical heavy ion-atom collisions

Positron lines were observed in heavy ion-atom collisions at bombarding energies close to the Coulomb barrier in subcritical systems with the sum of the atomic numbers of the colliding nucleiZ _u =Z ₁+Z ₂ being smaller thanZ _u =172. Each collision system, studied,²⁰⁸Pb +²⁰⁸Pb(Z_u=164),²³⁸U+¹⁸¹Ta(Z_u=165), and²³⁸Au(Z_u=171), exhibits the emission of two positron lines withZ _u -independent c.m. energies of ～ 258 keV and ～ 340 keV, and with widths of about 30 keV, superimposed on continuous positron spectra from nuclear pair decay and pair emission induced by the time changing Coulomb field of the collision. The production cross section of thee ⁺-lines rises with a high power ofZ _u (ocZ _u ²²), which is comparable to theZ _u ²⁰-dependence for the collision induced positrons.     

Variational method for electron excitation in ion-atom collisions

The variational principle is formulated for wave functions with complex time-dependent parameters. Their properties are illustrated by exactly solvable models. The problem of finding the relevant parameters is investigated. As an example we study the energy transfer to an electron during a symmetric ion-atom collision.     

Excitation in ion-atom collisions inside subfemtosecond laser pulses

We discuss new excitation mechanisms in energetic ion-atom collisions embedded in short laser pulses. For comparable duration and strength of the pulse and collisional interaction, the laser field will probe and modify the interaction between projectile and target. Coherence effects emerge, insight into reaction dynamics is gained, and new dynamical features are discovered. As an example, we show (i) how a propensity rule for s-p excitation can be dramatically changed, and (ii) how the presence of the laser pulse modifies the ionization process in ion-atom collisions.     

Stimulated emission of the coherent electromagnetic radiation by superconducting film

Coherent microwave radiation has been directly detected in the frequency range of 0.15–200 MHz from superconducting thin films excited by an oscillating magnetic field directed perpendicular to the film plane. Due to pinning, a metastable state of the vortex system can be set up in the superconducting films. Vortex-jump synchronization reached via their electromagnetic interaction with external resonant circuit causes the generation of the electromagnetic radiation.     

Information-theoretical description of charge-state distributions in heavy ion-atom collisions

Universal equations for asymmetric equilibrium charge-state distributions are derived using the maximum-entropy principle. They are tested on chlorine, bromine, and iodine projectiles in several gases at various incident energies. A single energy-independent parameter relates the rate of charge formation to the observed asymmetries.     

Generation of coherent electromagnetic radiation by superconducting films at liquid-nitrogen temperatures

Generation of coherent electromagnetic radiation by GdBa₂Cu₃O_7?x superconducting films is observed in the frequency range 1–10 MHz at the temperature of boiling liquid nitrogen. The generation is caused by the feedback synchronization of the jumps of Abrikosov vortices produced by a low-frequency external magnetic field. This offers new possibilities for the application of high-T _c superconductors in superconducting electronics.