X-ray measurement of laser fusion targets using least squares fitting

This paper presents an x-ray technique for measurement of opaque hollow microspheres used as laser fusion targets. We describe a nondestructive method for holding microspheres that enables microsphere rotation between x-ray exposures. We record film images of the microspheres using contact microradiography. We use computer image analysis for measurement of the microsphere characteristics, which involves mathematically modeling processes that relate the microsphere characteristics to film density and then applying a least squares fit of the model to the image data. We compared this measurement with the optical interferometric measurement for several glass microspheres and found measurement differences <0.3 microm for wall thickness and 0.1 microm for nonconcentricity.