Characterization of inner surface roughness for ICF capsules by backlit shadowgraphy

A backlit shadowgraphy technique has been developed, which can be used for nondestructive characterization of ice layer's inner surface quality for transparent ICF capsules. The physics of the bright band formation for single-layer shell is analyzed by optical theory. With raytrace code, Tracepro, simulated shadowgraphs of transparent single-layer shells are produced to investigate the relation between bright-band position and thickness or refractive index of shells. A setup has been established for backlit shadowgraphy, and experimental shadowgraphs of transparent single-layer shells are obtained, which have a distinct bright band. A code has been developed to analyze shadowgraphs, and the shell's inner surface power spectrum (1-D) is obtained, then its RMS surface roughness is calculated. These analyses in theory, simulation and experimental results prove the validity of the technique.