Vibrating Object Shape Measurement Base On A Grating Interferometer For Sinusoidal Phase-modulation

The sinusoidal phase-modulating (SPM) interferometry is that physical quantities are measured by analyzing interference signal with reference beams sinusoidal phase-modulated. The interferometry has some advantages, such as simple system, high-accurate measurement, strong antijamming capability and so on, thus it has been used to displacement measurement, vibration measurement, surface profile measurement, etc.In this paper, the diffraction and interference phenomenon of two grates and frequency principle are analyzed. The principle of grating-modulating measuring surface profile is introduced.Based on the principle of sinusoidal phase-modulating grating interferometer, in this paper a two-grating interferometer with sinusoidal phase-modulation is used for measuring a large movement of a surface profile of an object. Choosing appropriate optical element, by setting up and debugging this optical system, the movements of the surface profile of a plastic plate with sinusoidal phase-modulating are measured. The interference stripe patterns with different times are collected within one grating period.At last, according to the ways of phase-object optic reveling, a computer program is organized by the MATLAB soft. This program is for image processing, numeric calculation and figure plot, afterward the distribution of the phase is gained, farther more with the relation between surface profile and phase, the distribution of 2-D surface profile of an object is founded, at the same time the figure about surface profile is draw in the coordinate of three dimensions.Result from experiments, the resolution of this technique is in the order of ten microns and a 2-D surface profile of a vibrating object can be measured. So this method is more practicality than other ways.