2023-09-12 22:00:00
Ultrashort pulses constitute a new laser technology allowing access to a very original mode of laser-matter interaction compared to conventional, continuous lasers, or lasers delivering pulses with durations greater than a nanosecond. Ultrashort laser pulses cover a pulse duration range from femtosecond (10−15 s) to picosecond (10−12 s). These impulses are at the origin of very innovative applications in the field of materials processing. A distinction is then made between femtosecond pulses, usually lasting a few hundred femtoseconds, and picosecond pulses, lasting more than 1 ps. In this article, we will not discuss imaging applications, for which visualization without modification of the material is sought, an area where ultrashort technologies also play a role. We will also not address the field of very high energies, used for large research instruments such as the MegaJoule Laser (LMJ). The field of laser processes concerns a modification made to a material and rather addresses industrial applications of lasers. This modification can lead to material removal, called laser ablation. We will therefore emphasize the characteristics of laser-matter interaction in ultrashort mode and their interest in the development of applications.
In the case of ultrashort laser pulses, very original physics of laser-matter interaction leads to the need for very specific expertise for process control. Their development was made possible by numerous laboratory research results, associated with intense scientific publication activity. Even before the 2000s, the date of the effective start of the first uses of femtosecond pulses in ophthalmic surgery, innovative industrial applications were imagined and studied with the available means. The motivation for these studies was, and still is, the removal of technological barriers limiting the field of applications concerned. In particular, the “trademark” of femtosecond processes is the very high precision of machining, usually of the order of ten microns, but can quite easily reach a few hundred nanometers, and simultaneously the non-alteration of the materials outside the treated area.
The first period of development of femtosecond processes was therefore aimed at reaching the industrial stage. In France, several technical centers embarked on this path very early on, in a context of strong competition, mainly in Germany and Japan. Thanks to the development and marketing, since the 2000s in France, of laser sources adapted to industrial applications, these technologies have reached the maturity necessary to pass the milestone of the first industrializations. The applications concerned were mainly in the medical field, but the industrial production sector also took off very quickly. Femtosecond micromachining machines are now part of the catalog of many suppliers, especially in Europe and Asia.
Since the 2020s and the possibility of using multi-hundred-watt laser sources, “macro-machining” industrial sectors such as automobiles or aeronautics are now accessible to femtosecond technologies. Several major developments are expected in these areas, especially in the context of current efforts for a more environmentally friendly industry. Laser ablation techniques can, for example, allow a replacement of very polluting chemical erosion techniques. The productivity now achieved for the texturing of large surfaces makes it possible to consider applications for reducing mechanical friction (engines) or air resistance (airplane wings).
Ultrabref technologies are plural, the associated laser processes can be very different, they therefore require significant expertise. To enable the reader to find their way in this vast field of scientific and technological developments, we propose in this article the following route: we will first introduce the specific and original nature of femtosecond pulses. A more precise description of the mechanisms of laser-matter interaction will then allow us to penetrate to the heart of this specificity. We will then show the link between the understanding of the mechanisms and the possibilities for optimizing the processes. At this stage of the journey, the presentation of the wide variety of process implementations will make it possible to understand the breadth of the application field. Finally, we will end with a review of the main industrial sectors where femtosecond processes are deployed.
The reader will find a glossary and a list of symbols used at the end of the article.
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