1. Specific features of femtosecond pulses

The first property of ultrashort pulses that comes to mind is the possibility of obtaining very high peak powers. Indeed, even for a low pulse energy, if its duration is ultra-short, its power - the ratio of the two - can take on significant values. A peak power of 10 GW is reached for a pulse of 1 mJ and 100 fs. A very useful physical quantity for laser processes is the power or energy density, also known as fluence, and often expressed in W.cm ^-2 or J.cm ^-2 . These quantities take into account the surface area of the material on which the laser beam is focused. For example, the previous pulse, focused on a diameter of 50 µm, achieves a peak power density of 30 TW.cm ^-2 . This value exceeds the ablation threshold of all known materials, thanks to an average...