A laser-interferometer measuring displacement with nanometer resolution

In material science there are certain classes of problems that require strain measurement over base lengths as small as 100 /spl mu/m and still demand a resolution limit of about 10 microstrains. This paper presents an interferometric strain sensor that is able to cope with that demand. The optical principle is given, and the digital signal processing involved is detailed. Furthermore, some experimental data for crack-tip opening displacement measurements on micro cracks and the measurement of thermal expansion coefficients of copper is given.<
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