Enhancement of second-order optical nonlinearity in photo-darkened Ge25Sb10S65 chalcogenide glass by femtosecond laser light

The second-order optical nonlinearity of poled Ge25Sb10S65 chalcogenide glass was found to be 40–50% larger after femtosecond laser irradiation. The highest χ(2) was 11.4 pm/V. Raman spectral change indicated that centrosymmetric defects were created by fs light. These defects promoted the third-order optical nonlinearity of the glass and as a result, its second-order nonlinearity was also enhanced. The study shows that fs laser modification is an effective method of increasing the optical nonlinearity of photonic materials.