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

The paper presents an X-ray technique for measurement of opaque hollow microspheres used as laser fusion targets. Consideration is given to a nondestructive method for holding microspheres that enables microsphere rotation between X-ray exposures. Film images of the microspheres are recorded using contact microradiography. Computer image analysis is used 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. This measurement is compared with the optical interferometric measurement for several glass microspheres and it is found that measurement differences are less than 0.3 micron for wall thickness and 0.1 micron for nonconcentricity.