1. Different types of UV-visible lasers and related issues

Different types of amplifying media and different techniques can be used to obtain a laser source emitting radiation in the UV-visible range. However, with a few exceptions, as will become apparent in the remainder of this presentation, it is often more difficult, for technological as well as purely fundamental reasons, to operate a laser in the visible and especially in the UV range, rather than in the near- and mid-infrared domains.

At a fundamental level, the reason lies in the expression of the stimulated emission cross-section, σ _em , at the origin of the laser gain of any amplifying medium, written, for example, in the form (the so-called Fuchtbauer-Ladenburg expression) :