Using an Interferometric Profiler and Gage Block to Determine Sample Thickness

Preshot characterization of the thickness and form of material samples in targets for dynamic materials properties experiments presents unique challenges. Because of design limitations, the measurement tools currently used introduce increasing error as samples deviate from perfect flatness or thickness uniformity. Contact measurements such as height gages and micrometers, for example, are insensitive to thickness variations occurring over spatial scales smaller than the contact probes. In addition, they measure thickness but not form and often damage samples. Standard confocal microscopes overcome some of these problems but can only measure form on the side of the sample that they see. Also, by design, they consistently overestimate thickness because form errors on the side of the sample against the reference surface always prevent perfect contact with it. We are developing a technique that may prove to be superior to both of these methods at characterizing both thickness and form of samples with both imperfect flatness and nonuniform thickness using only an interferometric optical profiler, an inexpensive fixture, a gage block, and a commercial three-dimensional modeling software. The end result is a computer model of the actual sample.