Large refractive index change in silicone-based and non-silicone-based hydrogel polymers induced by femtosecond laser micro-machining

A Ti: Sapphire femtosecond laser with a pulse energy of 1.3 nJ at a 93 MHz repetition rate has been used to micro- machine optical gratings inside several silicone-based and non-silicone-based hydrogel polymers. By measuring the diffraction efficiency of the gratings at 632.8nm, we find as large as 0.06 +/- 0.005 average refractive index change within the irradiated area. (c) 2006 Optical Society of America.