Internal modification in transparent materials using plasma formation induced by a femtosecond laser

The fabrication of internal diffraction gratings with photoinduced refractive index modification in transparent materials was demonstrated using low-density plasma formation excited by a femtosecond (130 fs) Ti: sapphire laser (λ_p=800 nm). The refractive index modifications with diameters ranging from 1 μm to 3 μm were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than 2.0×10¹³ W/㎠. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred.