New applications of the interferometric strain/displacement gage

The Interferometric Strain/Displacement Gage (ISDG) is an established laser-based technique that measures the relative displacement between two gage points on a specimen surface. The gage points are reflective markers illuminated with a low-power He-Ne laser to form interference patterns that are monitored with a computer-controlled system. Features of the technique are short gage length (50 - 300 mu m) and no mechanical contact. Two new applications of the ISDG are described in this paper. The first is the measurement of strain on metal microspecimens that are 3 mm long with cross-sections typically 0.3 mm square. Details of the test procedure and results from 52 tests conducted as part of an ASTM-sponsored cross-comparison test are summarized. The second is strain measurement on 3.5 mu m thick polysilicon film specimens; this capability has enabled measurement of the Young's Modulus and the tensile strength of this material which is used in microelectromechanical systems (MEMS).