When laser pulse interacts with mater, it deposits intense energy which goes to the material in different ways depending on laser parameters and properties of target material. Of course, it induces thermal energy, electric breakdown etc. The advantage of femtosecond laser is mainly the pulse duration, there is not enough time for electron lattice coupling in case of metal targets, so one may investigate the local electronic effect in a better way [for dielectric electric breakdown and spectroscopy].
Are you talking about the processing of transparent materials?
I know the following: When a not too short pulse is focused in a transparent material you first get multiphoton-absorption (that is what you might refer to femtosecond ablation in case of a surface manufacturing).
But since the multiphoton-absorption creates free electrons, those can absorb the trailing part of the pulse directly (linear absorption). That is what I would call breakdown.
Depending on the length of your pulse, one or the other will be the predominant effect.
If I am not wrong, the laser induced breakdown ablation is generally used for spectroscopic analysis by which one can identify the chemical nature of the studied target material. It is also known as LIBS. By using a short pulse duration it is possible to distinguish the basic process from the secondary effects if any.
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