Research On Vibration-Resistance Technology For Optical Interferometry

Phase shifting interferometry (PSI) has been widely used and accepted as a fast and accurate non-contact metrology tool. It is widely used to measure optical element, optical system, detection of optical surface and the physical quantities(such as field of temperature, field of density) related with optical path difference .The underlying measurement principle of PSI is to determine the phase of the intensity signal in interferogram received at each pixel of an imaging device. With the regular move of PZT, it can obtain intensity signal of several interferograms. Then the optical path difference can be obtained with PSI algorithm and to use the phase value for each pixel to determine a height value for each pixel. A primary advantage of PSI is its high precision. With careful control of environmental conditions, measurement precision to the nanometer scale or below is possible with PSI. However, one of the most serious impediments to wider use and improve precision of PSI is its sensitivity to external vibration with the consequence that PSI has rarely been used in a manufacturing in-situ and some special situations, such as that the optical path is very long or the detected unit is very large. Instead, PSI has been relegated to use during post-manufacturing inspection. Combined with the research project of my tutor and to extend the use of interferometer and to develop the interferometry, in this paper, some studies on vibration-resistant for interferometry have been prior considered in creationary and exploring way.In this thesis, the general error sources for PSI are analyzed. We find that the relatively low-frequency vibrations at 50Hz and lower are the main problem through the analysis of the vibration sources in usual environment. A new vibration compensation method, phase modulating interference fringes fractionizing technology, has been put forward in a creative way. It simulates the fringe's move by the phase difference of signals. It can detect the fringe's move by 1/400 of the space of two neighboring fringes with fractionizing technology. A new mathematical and physical models based on the method are established. And the ways to carry out the models by full electric circuit are proposed. We build a close vibration compensation system which can successfully achieve the measurement of interference fringesmovement and -vibration compensation. It puts forward pre-setting fill-in pulses method to implement phase shifting with the same PZT. With this new method, the interference fringe can be stabilized at any pre-setting phase position. A new feedback algorithm is brought forward to overcome the instability of the system. It uses 3 times approaching vibration compensation method. A pigtail with laser coupling lenses as a point light source of interferometer is designed. It can be separately used to the body of interferometer. Experiments were carried out on a smooth mirror surface excited that the technique was found to be immune to vibration of serious vibrations at 50Hz or lower. Finally, the main resources of errors to influence the effects of vibration compensation and PSI measurement results are discussed in detail.