Raman and photoluminescence spectroscopies fo the porous silicon prepared in a hydrothermal solution with addition of titanium have been studied. Only a sharp single band near 520cm-1 appears in the Raman spectrum of the porous silicon when the exciting laser power is low and shifts to the red side with the increase of the laser power. If the laser power is increased to a critical value, the Raman band splits into two bands while the photoluminescence band splits also and the intensity of it increases enormously. We assign the two Raman bands to the lattice deformation-induced non-degeneracy of the LO and TO phonons. The laser-induced lattice deformation may result in the transformation of the porous silicon from a linear to a nonlinear optical material with a large laser-induced nonlinear optical absorption coefficient. It is found that the laser-induced transformation in the porous silicon is a reversible process. This may implicate some new applications of this material.