  The absorbed laser energy of a femtosecond laser pulse in a transparent
material induces a warm dense matter region which relaxation may lead to
structural modifications in the surrounding cold matter. The modeling of the
thermo-elasto-plastic material response is addressed to predict such
modifications. It has been developed in a 2D plane geometry and implemented in
a hydrodynamic lagrangian code. The particular case of a tightly focused laser
beam in the bulk of fused silica is considered as a first application of the
proposed general model. It is shown that the warm dense matter relaxation,
influenced by the elasto-plastic behavior of the surrounding cold matter,
generates both a strong shock and rarefaction waves. Permanent deformations
appear in the surrounding solid matter if the induced stress becomes larger
than the yield strength. This interaction results in the formation of a
sub-micrometric cavity surrounded by an overdense area. This approach also
allows one to predict regions where cracks may form. The present modeling can
be used to design nano-structures induced by short laser pulses.
