Nondestructive Evaluation (NDE) for Large Silicon Carbide (SiC) Optical Structures

It is increasingly apparent that silicon carbide (SiC) is one of the preferred next-generation mirror-substrate materials for space telescope applications because of its superior material properties and the relative ease with which it can be utilized to fabricate lightweight structures. However, to take full advantage of these attractive SiC characteristics, there is a need for a rapid method of non-destructive evaluation or testing (NDE or NDT) to verify the integrity of the completed mirrors. Xinetics proposes a collaboration with Argonne National Laboratory to develop NDE methodology applicable to large SiC optical structures for the characterization of surface/sub-surface defects, internal defects, and internal stress. Sample SiC structures will be carefully fabricated with well-controlled defects or stresses, Laser Back Scatter and Phase Array Ultrasound will be used to examine the samples for defects, and Laser-Generated Ultrasound, employing Rayleigh and Lamb waves, will be used to measure the internal stresses of the samples.