Lasers sources Principles, properties and applications

The invention of the ruby laser in 1960 by T. Maiman was the culmination of fundamental research into the interaction between light and matter, which had been underway since the beginning of the 20th century. In the space of sixty years, lasers have become a familiar object used in an ever-growing number of applications, while retaining their fascinating character. The common representation of a laser, popularized in particular by the cinema, is that of a ray of colored light, which illustrates two fundamental properties of lasers: the specific nature of the spectrum – the frequency content –, and the directivity of the radiation. Laser radiation is therefore very different in nature from conventional light sources (incandescent bulb, light-emitting diode), which generally have a broad spectrum and low directivity. Lasers come in all sizes, from nanostructures measuring just a few tens of nanometers to controlled fusion laser systems occupying buildings several hundred meters high. The types of radiation emitted are also very diverse, both in terms of wavelengths (from the X-rays and far UV of excimer lasers, to the infrared of CO ₂ lasers), and the temporal structure of laser radiation (from continuous lasers to ultra-short pulse sources: femtosecond (10 ^-15 s), or even attosecond (10 ^-18 s)). Lastly, the instantaneous luminous powers emitted vary over a very wide range, from nanowatts (10 ^-9 W) to exawatts (10 ¹⁸ W). Moreover, in a fast-changing technical and industrial context, the fields of application for lasers have greatly diversified, ranging from machining to telecommunications, via surgery and today's major energy challenges. To provide an overview of laser sources, the first part of this article reviews the common principles of lasers: light amplification mechanisms, the cavity effect, and the spatial and temporal shaping of laser radiation. The second part gives a general overview of laser sources, according to their field of application.

At the end of the article, readers will find a glossary and a table of symbols used.