A laser is a light amplifier. The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. A branch of science and engineering called quantum electronics has grown to cover the study of lasers and their applications. Since our interest in lasers is in using them for material processing, we do not have to learn every detail of their operation [1]. A general outline, however, is extremely useful in understanding the characteristics of the various types of lasers used to affect materials.