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MANUFACTURING with short pulse lasers
ADVANCED MANUFACTURING BY ULTRASHORT PULSE LASERS
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Sylvain LECLER * ICube academic research Institute, UMR University of Strasbourg, CNRS, INSA Strasbourg, ENGEES, Strasbourg, France * sylvain. lecler @ insa-strasbourg. fr
By achieving extremely high peak power with remarkably low energy, ultrashort pulse( USP) lasers have unlocked innovative and original approaches for material structuring and micromachining. After explaining the fundamental principles of how these ultrashort pulses interact with matter, this discussion will present their primary applications and the associated challenges.
https:// doi. org / 10.1051 / photon / 202613754
This is an Open Access article distributed under the terms of the Creative Commons Attribution License( https:// creativecommons. org / licenses / by / 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Lasers have long been used in manufacturing for cutting, drilling, welding, and thermal annealing of a wide range of materials, from polymers to metals. However, with Continuous Wave( CW) and nanosecond pulse lasers, the absorption rate is highly material-dependent. Additionally, a thermally affected zone inevitably forms around the processed area. Ultrashort pulse lasers where pulse durations range from 10 femtoseconds( 10 −15 s) to 100 picoseconds( 100 −12 s) exhibit fundamentally different behavior. Due to nonlinear absorption mechanisms( such as multiphoton absorption, avalanche ionization, or tunneling), the laser pulse can be absorbed by virtually any material once a specific fluence threshold is reached.
This versatility makes USP lasers " universal tools."
Another key advantage is that USP laser processing is often considered non-thermal. While it is commonly stated that the ablation process is " faster " than thermal processes, this is not entirely accurate. To understand why, it is essential to recognize that the material ' s response primarily depends on the peak power density( W / cm ²). With USP lasers, exceptionally high peak power Ppeak( W) can be achieved with relatively low pulse energy( E [ J ]) due to the ultrashort pulse duration( Δτ): P peak = E / Δτ( see Figure 1). For example, 1 joule is the energy emitted by a basic LED in less than a second, an almost negligible amount. When this 1 joule is concentrated into 1 picosecond( 10 −12 s), it results in a peak power of 10 12 W, or 1 terawatt( TW).
This immense peak power is further spatially concentrated using an f-theta lens or microscope objective, focusing it onto an area of just a few square micrometers. This enables the achievement of extraordinarily high peak power densities( W / m ²). In the example above, concentrating the energy onto a 10 µ m ² surface yields a peak power density of 10 18 W / cm ²( 10,000 petawatts / cm ²). In practice, with a pulse duration of 300 femtoseconds, only a few microjoules from a 1030 nm Ytterbium laser are sufficient to ablate metals or transparent glass. Since each pulse involves only a few microjoules, the thermally affected volume remains minimal. The extraordinarily high peak power density allows for the modification, fusion, or ablation of any material, but only within a highly confined volume due to the low energy involved.
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