1. The specific nature of laser-matter interaction in ultrafast mode

The first property of very short pulses that comes to mind is the possibility of obtaining very high powers, since even for a low energy, if the duration is even lower, the ratio of the two, the power, can take on significant values. A peak power of 10 GW can be achieved for a pulse of 1 mJ and 100 fs. The important physical quantity for laser processes is the power density (often expressed in W/cm ² ), which takes 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 , which exceeds the ablation threshold of all known materials. Note that this result is achieved with a very modest average power, which may not exceed one watt (depending on pulse rate). The ability...