Invented in 1960, the laser has become a very important tool in manufacturing. Lasers in the context of this book can be regarded as energy converters that convert common forms of energy (e.g., electrical discharge or conventional light emitted by ash lamps) into a unique kind of high-quality coherent energy elds. The laser active medium is pumped by conventional energy. Due to stimulated emission in a resonator setup, the generated photons are multiplied. As all photons provide the same wavelength and phase, the resulting electromagnetic wave is characterized by a high degree of coherence, a very narrow spectral distribution, and low divergence. This unique behavior results in very good focusing capabilities, and the resulting power densities in the focus of a high-power laser eld can reach 1016 W/cm2 easily. Those high intensities can lead to the melting and evaporation of almost all kind of materials, making laser sources an interesting tool in materials processing.