Fabrication of Fresnel zone plate embedded in silica glass by femtosecond laser pulses

We fabricated the Fresnel zone plate by embedding voids in silica glass. We investigated the focusing properties by launching a He-Ne laser beam into the zone plate. The spot size of the primary focal point was 7.0 mum and agreed with the theoretical value of 6.1 mum. The diffraction efficiency was 2.0 %. This technique enables us to make alignment free micro-scale lenses inside bulk materials.