Annular phase filter based low coherence interferometer for the profile measurement of the transparent ICF shells

Axial resolution improvement in the low coherence interferometry (LCI) with a three-zone annular phase filter is demonstrated. The sidelobes resulting from the super-resolving features of the phase filter can be suppressed by the coherence gate of the LCI. The parameters of the filter are optimized to increase the axial gain GA as large as possible while maintaining an acceptable value of the Strehl ratio S and the transverse gain GT through the numerical simulations. The effect of the actual broadband spectrum and Gaussian amplitude profile of the incident light on the performance of the designed filter is investigated. With the designed filter, the experimental axial gain is 1.25 while the intensity loss is about 5.5 dB with the mirror sample, which is also verified with the dimensional measurements of a transparent inertial confinement fusion (ICF) shell.