Optical EngineeringDigital laser microinterferometer and its applications
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A universal digital laser microinterferometer is presented, which can measure the shape, displacement, and strain and stress of microelements and microelectromechanical systems (MEMSs). This device can measure microelements with either a smooth or a rough surface. The method is based on laser interferometry (for smooth surfaces) and laser speckle interferometry (for rough surfaces), incorporating a diode laser, a long-distance microscope, a CCD camera, and a high-precision phase-shifting technique. The measuring system can be utilized to measure shape and out-of-plane displacement for samples with smooth surfaces, and with minor modification it can be applied to investigate out-of-plane and in-plane displacements for samples with rough surfaces. The theory and methodology of the universal digital laser microinterferometer are described. In particular, calibration and error compensation are introduced. The usefulness of the microinterferometer is demonstrated by examples of shape and displacement measurement for different MEMSs and microelements.