A review of models describing the interactions of ultra-cold atoms and laser light is given. Both semi-classical and fully quantum models are presented with particular attention given to the introduction of local field effects. Some possible effects of self-localization and guiding, consequences of such interactions, are discussed.

New generation telecommunications satellites are designed to cater for constantly increasing number of users, asking for higher and higher bit rates, in the same frequency multiplex. The combination of these two tendencies implies increasing power levels in the RF equipment downstream from the power amplifiers. In this situation, different types of discharge phenomena can occur inside the microwave devices. The consequences may be link budget degradation or even damage to the equipment. Two kinds of discharges can occur depending on the pressure range:

An experimental and numerical investigation is made of multipactor discharges in a coaxial waveguide. Particular attention is given to the determination of the multipactor threshold and the distribution of the impact energy of the electrons. Simulations are carried out for different parameters of the secondary emission coefficient of the electrode surfaces. This makes it possible to determine these parameters through a comparison between the numerical and experimental results. The comparison also shows that the observed multipactor is mainly of polyphase (non-resonant) nature and represents a mixture of single- and double-surface multipactor discharges.

We investigate the main physical properties of microwave corona breakdown in strongly inhomogeneous electric fields. The focus is put on numerical and approximate analytical calculations of the breakdown threshold in an exponential ionization profile, which is the basic form of the ionization profile caused by the field enhancement around irregular and curved conducting objects. The breakdown threshold is a value associated with a certain plasma density profile. We explain the major characteristics of the density profile, its dependance on pressure and the interplay of diffusion and attachment. For lower pressures the diffusion distributes the electrons from regions of high ionization frequency to regions of weak ionization, where the attachment acts as a sink. For high pressures the diffusion becomes negligible and the breakdown threshold is set by the equality of the ionization and attachment frequencies in the high field region.

A detailed analysis is made of the effect of reflection of low-energy secondary emitted electrons on the susceptibility diagrams for multipactor breakdown between two parallel metal plates. The problem is studied using both analytical and numerical methods. The left boundary of the first resonance zone for the multipactor is shown to be significantly modified when electrons with impact energy of the order of their initial energy are completely reflected. Specifically, in this case, the multipactor avalanche may grow even when the gap between the metal plates is very narrow if the applied RF voltage is high enough to provide electron acceleration up to energies exceeding the first crossover energy of the secondary emission curve. This effect is proposed as a means for experimentally investigating the reflection properties of low-energy electrons from the surface of different materials.

Multipactor discharges in waveguides with wedge-shaped cross section are studied both analytically and by means of numerical simulations. It is shown that similar to the case of a rectangular waveguide, a trapped electron trajectory is possible in a wedge-shaped waveguide; however, this trajectory is unstable with respect to small deviations of launch time and initial position of the electrons. Numerical simulations have been carried out taking into account a spread of the electron initial velocity and the action of the radio frequency magnetic field on the electron motion. The simulation results show that growth of the multipactor avalanche is possible in the wedge-shaped waveguide; however, the multipactor threshold in terms of the transmitted power is higher than for the rectangular waveguide with the same propagation constant and cross-section area.