<title>Conventional and fiber optics interferometry for vibration mode analysis</title>

Abstract

The visualization and analysis methods for studying vibration modes of macro and micro scale objects with spectrally reflecting and scattering surfaces, developed at the Institute of Micromechanics and Photonics of the Warsaw University of Technology, are presented. Silicon technology prepared microspecimens (AFM cantilevers and active PZT micromembranes) are investigated using two-beam time-average interferometry. Vibration modes of flat and non-flat surface microelements are displayed using four and five-frame temporal phase stepping methods. The calculated contrast of vibrating object interferograms provides the information on the vibration amplitude. Scattering surface objects are studied by time-average fiber-optics digital speckle pattern interferometry (DSPI) with heterodyning. Sinusoidal phase modulation introduced at the object vibration frequency enables quantitative analysis of the amplitude and phase of sinusoidal type vibrations. Laser diode modulation and/or single mode fiber stretching is applied for that purpose. For low vibration amplitudes (a<2J2O) the method using linear approximation of the zero order Bessel function provides an automatic analysis tool for quantitative estimation ofthe vibration modes.