ABSTRACT
The light amplification by stimulated emission of radiation (LASER) suggests that the device is an amplifier. However, it is not true; it is an oscillator. Moreover, replacing amplification by oscillation could bring funny associations. The year 1960 witnessed the beginning of a new revolution in optics. The effect of stimulated emission, predicted in 1917 by Albert Einstein, was finally implemented in practice. The discovery of the new optical device, called LASER, was preceded by several theoretical works of Ch. Towns, N.G. Basov, and A.N. Prokhorov, who won a Nobel Prize in 1964. The chapter provides some elementary knowledge about gas laser operation. It includes a description of properties of neutral and weakly ionized gases. The chapter describes gas spectroscopy and optical gain conditions. It presents the simple model of a LASER action and reviews different kinds of LASER excitation.
