ABSTRACT
Advances in semiconductor laser diodes have given a new impulse in the research for visible solid-state laser sources with the opportunity to realize compact devices. There is an important potential interest for compact visible sources emitting in the blue, green or red in many applications. Low-power compact continuous-wave (cw) visible lasers are the key components in the development of undersea optical communications, high brightness displays, high-speed printers, high-density data storage, for medical applications and the environment (control of pollution), while high-power (cw or pulsed visible) devices are required for spectroscopy, materials treatment or surgery. Semiconductor laser diodes emitting in the near-infrared operating stably at room temperature require simple electric power supplies providing ideal excitation sources for miniaturized devices. Several optical processes such as parametric oscillation, stimulated Raman scattering or frequency mixing, or frequency conversion in a non-linear crystal, allow laser emission in the infrared range to be converted into visible laser radiation. Frequency conversion or, more precisely, second-harmonic generation (SHG) in a non-linear crystal will be the subject of this chapter. An infrared cw laser emission can be converted into a visible laser light either by intracavity frequency doubling (ICFD) or by self-doubling. These new approaches are promising in work to achieve compact all-solid-state lasers emitting in the blue-green spectral range. The basic principles of SHG will be given in the first part. Then ICFD will be compared to self-doubling in their principles and performances. For a deeper understanding, the reader can refer to several reference textbooks on non-linear optics [1–5], laser materials [6] and engineering [7,8].
