The LASER light source, whose name is based on "Light Amplification by Stimulated Emission of Radiation", is the most important device in almost all photonic applications. First built in 1960 [6.1-6.5] it allows the generation of light with properties not available from natural light sources. Modern commercially available laser systems allow output powers of up to 10 20 W for short times with good beam quality and of several kW in continuos operation, usually with less good beam quality. Very short pulses with durations smaller than 5 · 10 −15 s, wavelengths from a few nm in the XUV to the far IR with several 10 µm, pulse energies of up to 10 4 J and frequency stability's and resolutions of better 10 −13 can be generated. The laser prices range from $ 1 to many millions of dollars and their size from less than a cubic mm to the dimensions of large buildings.The good coherence and beam quality of laser light in combination with high powers and short pulses are the basis for many nonlinear interactions, but the laser is a highly nonlinear optical device itself, using nonlinear properties of materials as described in the previous chapters. Therefore, the fundamental laws treated in Chap. 2 for the description of light as well as the description of linear and nonlinear interactions of light with matter in Chaps. 3, 4 and 5 are the basis for the analysis of laser operation and its light properties. Therefore, the theoretical description of laser devices represents an application of these laws and can be presented in this chapter in a compact form. For details the related sections of the previous chapters should be consulted. The different lasers and their constructions, as well as the resulting relevant light and operation parameters, are described and the consequences for photonic applications are discussed. Finally, possible classifications are given and safety aspects are mentioned. For further reading see [M6, M16, M17, M23-M25, M27, M28, M30, M33, M43, M44, M49, M50, M58-M65].
