Laser sources with emission in the Visible region

In recent decades, laser technology has greatly increased the application fields ranging from medicine to telecommunications, industrial processes, to frontier research. However, the challenges posed by the new millennium require an increase of effort, both in terms of economic investment and human resources, for the development and the realization of more and more compact, powerful laser sources, with sustainable production costs and, last but not least, with emission at specific wavelengths. To date, laser systems with solid bulk activated with ions of Rare Earths (REE), with infrared emission, are commercially available, but few are the laser sources with direct emission in the visible (VIS). The latter development has been mainly a disadvantage from the difficulty of finding pumping systems with a wavelength compatible with those of absorption of the active media, crystalline or polycrystalline matrices doped with REE ions. The advent of laser diodes, based on InGaN, has reactivated this field of investigation. Among the most important applications of VIS lasers there are optical atomic clocks.