Fresnel zone plate method for measuring lens transmission wavefront power spectral density

摘要

The optical components employed in high power density solid-state laser for inertial confinement fusion (ICF) must be measured accurately to provide the high resolution measurement neccessary to detect mid-spatial-frequency errors in the wavefront. The use of a Fresnel zone plate (FZP) technique to measure lens transmission wavefront power spectral density (PSD) in mid-frequency domain is disscussed. FZP can provide reference sphere with high-precision, in the meantime greatly shorten air space, thus reduce the effect of vibration and air turbulence, therefore is of great importance for lens transmission wavefront PSD measurement, especially for lens with long focal length used in the ICF facility. To verify the accuracy of the measurement, a comparison experiment of the FZP measurement with results from a Fizeau sphere interferometry method is carried out. Measurement results show excellent agreement, which proves the validity of this method. Finally, measurement uncertainty due to FZP fabrication process is analyed. Analysis of the FZP test showed the overall accuracy of 4.5nm RMS for a sphere lens with 1.5 m focal length and Φ70mm clear aperture. Thus, the measurement accuracy using the proposed FZP method is proved to be very high, FZP can therefore be used to measure lens transmission wavefront PSD accurately.