Femtosecond Laser Direct Writing of Volume Fresnel Zone Plates

We describe a method of using femtosecond laser for direct writing of volume Fresnel zone plates with high diffraction efficiency. A volume zone plate consists of a number of Fresnel zone plate layers designed to focus light coherently to a single spot. We fabricated both low numerical aperture (NA) and high NA volume zone plates, resulting in a significant increase in overall diffraction efficiency. The performance of the volume zone plate is also simulated using the Hankel transform beam propagation method (Hankel BPM). The results show an excellent agreement with the scalar diffraction theory and the experimental results. The numerical method allows more comprehensive studies of the VFZP parameters to achieve higher diffraction efficiency.