Coherence, Dipole Radiation and Laser

Abstract

This chapter is focused mainly on coherence, a vital concept if one wants to go beyond a rudimentary understanding of waves; the notion is rooted in the statistical properties of a wave. We also elucidate how mixing of real physical waves leads to unexpected relationships: for example, it would be disastrous if the members of a choir managed to sing in perfect tune. This is related to the difference between light from a lamp compared to laser light. A computer program is provided for numerical explorations of both temporal and spatial coherence. The discussion of coherence is followed by a conceptual explanation of how electric charges in motion may lead to radiation of electromagnetic waves, and the radiation diagram for a dipole antenna is presented. The chapter concludes with a brief description of the basic principles for generating laser light.