In this paper, we present the investigation results on laser-induced structural modifications in a BK7 glass sample
(OHARA, S-BSL7) by use of a femtosecond laser and a CO2 laser system. A femtosecond fiber laser system (wavelength: 1.06 μm, pulse duration: 250 fs) generates 1 MHz ultrashort laser pulses with a pulse energy up to 2 μJ, and a CO2 laser system generates CW (continuous wave) laser beam with a wavelength of 10.6 μm. Both laser beams were simultaneously irradiated on a BK7 glass substrate (30 mm × 5 mm × 0.7 mm thick). The structural modifications regions were created by translating the glass sample perpendicular to the laser axis with a distance of 1 mm and a scan speed of 0.1 mm/s. The dependence of structural modifications on the laser energy of femtosecond laser pulses and the power of CO2 laser beam were investigated. The results have demonstrated that the refractive index change region with the width of 3 μm was created with simultaneously irradiation of two laser beams although the structural modification regions, which were produced with only femtosecond laser pulses, were surface ablation. And the surface ablation regions were changed to the refractive index change regions as the energy of CO2 laser beam increase to more than 2W.