**6. Conclusions**

In this chapter, we review the fabrications of various periodic nanostructures, that is, ripple structures of self-organized nanodots, nanolines, nano-cottons, and nano-bricks on the surfaces of ITO thin films after fs laser pulse irradiation. The ITO films with surface ripple structures were successfully prepared at a fluence of 0.1 mJ/cm2 and numbers of pulses from 5 × 103 to 3 × 106 , without scanning. The fs laser-annealed ITO films exhibited a great enhancement in electrical conductivity (~30 times) due to the presence of indium-like clusters in ripple structures. In addition, the ITO films obtained nanodot structure at a fluence of 0.1 mJ/cm<sup>2</sup> and a pulse number of 3 × 106 and nanoline structure at a fluence of 0.2 mJ/cm<sup>2</sup> and a pulse number of 2 × 107 . The fs laser-annealed ITO films presented interesting anisotropic transmission properties (*TL*⊥*<sup>P</sup>* <sup>&</sup>gt; *TL*//*P*) because the nanostructures functioned as a metallic grid that induced the electron movement along the nanolines and Joule heating loss to block the EM wave for the case of L//P (i.e., the direction of nanolines, L, is parallel to the polarization direction, P, of fs laser pulses). Moreover, nanostructures with cotton, brick, and ripple forms are generated on the surface of ITO films by controlling the laser fluences from 60 to 646 mJ/cm2 and a scanning speed of ~12.5 pulses/μm, which produce cyan, yellow, and orange colors. These nanostructures can significantly attenuate blue light, and thus, they are possible for applications such as eye protection and information security.
