Direct writing waveguides inside YAG crystal by femtosecond laser

A 120 fs Ti–sapphire laser was used to fabricate waveguides in YAG crystal. A 7 mm long waveguide was written at a position of 100 μm below the surface, which shows multimode propagation at 633 nm with optical attenuation of about 0.2 dB/mm. The light guiding occurs in the region around the visible laser-damaged region, indicating that the light guiding area is induced by stress. The waveguide exhibited strong birefringence property with maximum magnitude of about 1.5 × 10−5. Infrared and Raman spectroscopy analysis indicate there is no change in chemical composition in laser-modified zone.