Abstract
A review is given of the excitation anisotropy in atomic or ionic level population, or alignment, and its effects on the line intensity : anisotropic intensity distribution and polarization. We take the optical excitation as an example of producing alignment and show various features of its effects. For other anisotropic-excitations, collisional excitation by electrons and charge transfer excitation of ions, latest results of the theoretical and experimental studies are presented. Relaxation of alignment is brought about by several mechanisms : disalignment by atomic collisions and by trapped radiation is understood fairly well, while nothing is known about electron collision and ion collision.
