Abstract: A femtosecond laser produces ultrashort pulses and ultrahigh electric fields. Various nonlinear effects, such as multiphoton absorption, multiphoton ionization, self－focusing and so on will occur when this laser radiation interacts with matter. We describe the novel phenomena and mechanisms of single beam femtosecond laser induced polarization－dependent nanogratings, periodic nanovoid structures along the propagation direction of the laser beam, and the alignment of nanoripples formed on the surface of crystals, which were all discovered recently.