Null interferometric microscope for ICF-capsule surface-defect detection

Isolated defects on the surface of the inertial confinement fusion (ICF) capsule reduce the probability of ignition. Here, to the best of our knowledge, we present the first null interferometric microscope (NIM) for direct and large-field surface defects detection on ICF capsules. The planar reference mirror in conventional interferometric microscopes is replaced by a spherical reference mirror to achieve null interference in the full field of view. Further, via the use of a short-coherence light source system, parasitic fringes are avoided. The feasibility of the NIM is verified via experiments on a 0.7 mm diameter capsule. A 1 mm diameter ICF capsule is also tested by the NIM to prove that the NIM has the ability to measure capsules with different diameters.