Lasers ¿half a decade of development

Laser light has a high degree of spatial coherence and can therefore be beamed sharply with little divergence over large distances. It is also coherent in time in much the same way as an r.f. oscillation. In these two respects it differs from ordinary light, which has no coherence either in space or in time and, in the language of the radio engineer, is broadband noise at optical frequencies.