ABSTRACT
There is a fundamental dependence of the laser-matter interaction on the
focusing conditions: either the laser beam is tightly focused inside a trans-
parent material or it is focused onto the surface. In the laser-surface interac-
tion temperature is a maximum at the outermost atomic layer at the sample-
vacuum boundary. Therefore if the absorbed energy density in the skin layer
is in excess of the ablation threshold the ablated atoms expand and leave
the laser-excited zone. In the confined interaction mode the zone contain-
ing the high energy density is enclosed inside a bulk of cold and dense solid.
For this reason the laser-affected material remains confined inside pristine
crystal. There are different ways for inducing the changes in properties of a
bulk solid by laser action. First, non-destructive and reversible phase transi-
tions (photo-refractive effect, color-centers, photodarkening in chalcogenide
glasses etc.) can be induced by lasers at the intensity below the damage
threshold. In this case an optical probe can detect the laser-affected zone
afterwards. If the structure is very small ( μm3 in volume) it can be used as amemory bit for high-density three-dimensional optical storage. The irre-
versible structural changes may be produced at high intensity well above the
optical breakdown threshold. It was demonstrated [Juodkazis et al., 2006;
Gamaly et al., 2006] that the unique conditions of extremely high pressure
and temperature with record high heating and cooling rates are created in
the energy deposition region that may result in formation of new states of
matter. Strong shock wave is generated in the interaction region propagating
into the surrounding cold material and compressing it. Shock wave propaga-
tion is accompanied by compression of the solid material at the wave front
and decompression (rarefaction wave) behind it leading to the formation of
a void inside the material. Compressed material in the form of a shell sur-
rounds the void. Careful investigation of thematerial in the compressed shell
recently revealed formation of new crystal non-existent before [Vailionis
et al., 2011].
