Lasers: An Overview

The first lasers appeared in 1960-61 when Javan, Bennett, and Herriott of Bell Telephone Laboratories announced the helium-neon laser just after Theodore Maiman, working at the Hughes Aircraft Corpor- ation, had made a practical ruby laser. In little over a year later a semiconductor laser had been developed more or less simul- taneously in Britain and the USA. Foundations An atom may be represented by a Bohr model: Fig. 1 shows that of a hydrogen atom. Bohr con- sidered one electron of charge -e and mass rn, moving with speed v, and acceleration v2/ r in an orbit around a central nucleus of charge +e. In classical physics, charges undergoing acceleration emit radiation and would, therefore, lose energy. On this basis, the electron would spiral towards the nucleus and the atom would collapse. Bohr therefore suggested that in those orbits where the angular momentum is a multiple, n, of 11/2n, the energy is constant. In the early 1920s, de Broglie proposed that an electron may be ...