Energetic characteristics of radiation of oscillating...

1. Introduction

[2] The problem on radiation of sources moving in homogeneous stationary media has been actively studied during many decades. The main attention was drawn to the analysis of the radiation of charged particles and their beams and also sources having this or that multipole moment. The results obtained in this field are presented in many monographs and papers [see, e.g., Afanasiev and Kartavenko, 1998; Afanasiev et al., 1999; Bolotovskiy, 1957; Carusotto et al., 2001; Frank, 1981; Ginzburg, 1987, 2002; Stevens et al., 2001; Zrelov, 1968]. It should be noted, however, that in the major part of the problems considered earlier the source was assumed to be static in its own reference system (i.e., it has no "proper" frequency). In such case (if one can neglect the irregularity in the source motion) the radiation at the given frequency exists only in the situation when the source motion velocity exceeds the phase velocity of the electromagnetic waves of this frequency (the Vavilov-Cerenkov radiation). In the case of a moving source oscillating in the "proper" reference system, the situation becomes principally different. Naturally, such source radiates at any velocity of the motion, but the radiation characteristics depend on it in a very significant way. Such problems are of an interest both for development of the theory and for experiments in various regions of physics. In particular, they present an interest for the analysis of radiation processes in the ionospheric plasma. In this case the antenna of a spacecraft, for example, may serve as an oscillator of the dipole type. A radiating moving atom presents another example of this kind.

[3] Various aspects of the theory of the radiation of oscillators moving in some simple media have been considered in publications [see, e.g., Frank, 1942, 1981; Ginzburg and Frank, 1947a, 1947b; Tyukhtin, 2004a]. This paper is dedicated to the analysis of the influence of medium characteristics on the radiation power of the oscillator and its spectral density. So we will restrict ourselves by the consideration of the case of an oscillating electric dipole uniformly moving in the direction of its dipole moment. Such formulation of the problem makes it possible to reveal principal physical regularities and, at the same time, to avoid too cumbersome mathematical expressions.

[4] Section 2 of this paper contains general expressions applicable to motionless medium with an arbitrary frequency dispersion. The main features of the cold plasma case are also noted. Section 3 is dedicated to the case of the medium with the dispersion of a resonant type. The situation when not only the oscillator is moving but the surrounding medium as well is considered in section 4.