We demonstrate maskless, single-step fabrication of strongly birefringent Fresnel zone plates by focusing of femtosecond laser pulses deep within silica substrates. The process allows us to produce alternate zone rings directly by inducing a local refractive-index modification of the order of <i>n</i>~10<sup>-2</sup> . The embedded zone plates shown in this Letter exhibit efficiencies that vary by as much as a factor of ~6 for orthogonal polarizations. Focal lengths of primary and secondary foci are shown to compare well with theory.
© 2002 Optical Society of America
(130.1750) Integrated optics : Components
(140.3390) Lasers and laser optics : Laser materials processing
(220.3630) Optical design and fabrication : Lenses
(320.7090) Ultrafast optics : Ultrafast lasers
Erica Bricchi, John D. Mills, Peter G. Kazansky, Bruce G. Klappauf, and Jeremy J. Baumberg, "Birefringent Fresnel zone plates in silica fabricated by femtosecond laser machining," Opt. Lett. 27, 2200-2202 (2002)