Near-UV and visible solid-state lasers

More and more scientific journals and conferences emerged in the late 1990s and early 2000s, and more and more articles are devoted each year to the discovery, development and applications of new laser systems. Among these, lasers based on solid materials, be they dielectric or semiconductor materials, crystals, glasses or transparent ceramics in the form of solid blocks, thin layers of varying thickness or fibers of varying thickness, are becoming increasingly important. In fact, most conferences devoted to laser sources and their applications today deal almost exclusively with systems based on solid materials. As a result, solid-state laser sources have invaded our daily lives, sometimes surreptitiously, and in all fields.

That said, certain types of source operating in particular wavelength ranges have taken the lead over others, firstly because of the applications to which they lead, but also, very often, for purely technological reasons. This is the case, for example, with solid-state laser sources operating in the mid-infrared around 1.54 μm. In fact, this wavelength range is the one chosen for transmitting information via optical fibers, firstly because it corresponds to a minimum attenuation of the silica fibers used for this application, but also because it is a so-called eye-safe range and allows this type of laser to be used in free space. This is also the case for laser sources operating in the near infrared around 0.8 and 1.05 μm. Today, these laser sources are at such an advanced stage of development that, thanks to the energies and peak powers they deliver or will soon deliver, we can already envisage the construction of pocket gas pedals for more selective therapy and more precise imaging of cancerous tumors, or even nuclear fusion or lightning guidance.

On the other hand, solid-state lasers in the UV-visible range (particularly below 650 nm), while offering many potential applications or already under development, are still in their infancy because the materials they are made of are often at their limits of use or have not yet been discovered.

This article focuses on solid-state laser sources emitting in the UV-visible range, and the possibilities and limitations they offer. The presentation will be divided into four parts. The first part will be devoted to a brief description of the different types of laser sources emitting in the UV and visible range, and the problems associated with them. This will be followed by an overview of solid-state laser sources in which the laser material itself emits directly in the UV-visible range. These include large-gap semiconductor laser diodes, rare-earth ion lasers emitting tunable radiation in the near-UV range, and rare-earth ion lasers emitting at fixed wavelengths from blue to deep...