The Characteristic of Birefringence and Optical Loss in Femtosecond-Laser-Induced Region in terms of Nanogratings Distribution

Femtosecond (fs) laser induced nanogratings formation can be applied to fabrication of complex birefringent optical elements, such as micro-arrayed waveplates, because birefringence appears in the region of nanogratings formation. For improvement of the quality of birefringent optics, it is important to find an optimized laser processing condition to obtain larger birefringence without loss of optical transmittance as possible. Therefore, it is important to elucidate the relation between birefringence, optical transmission loss and laser processing conditions. In this study, we have investigated the distribution of nanogratings in the modification by fs laser irradiation, retardance and transmittance under various processing conditions. We found that continuously distributed nanogratings with a homogeneous period in a modified region contribute to generation of birefringent region with larger retardance and higher transmittance.