Collision lasers on atomic transitions

This paper reviews the research of cw collision lasers on transitions of atoms and atomic ions and presents characteristics of systems that are considered to be collision lasers. Literature data on "relaxation" and "mixing" of levels by collisions with heavy particles are discussed, with particular attention to the relaxation of metastable levels. The major problems in the development of efficient cw collision lasers are analysed, including difficulties in realising discharges suitable for pumping collision lasers. The possibility of further advances in collision laser development is discussed.