White-light Interferometers Based On A High-performance PZT Stage And Their Applications

As a kind of non-contact,high-precision and high-speed measurement approach,white-light scanning interferometers(WLSI)and spectral resolved interferometers(SRI)are widely used to measure the thickness of glass plate in recent years.With the development of interference technology,more research are focused on improving detection accuracy and increasing detection thickness.When the thickness of a glass plate is in a region of a few millimeters,the interference signals of WLSI and SRI exhibit complicated waveforms because of strong dispersion effect of the glass plate.In WLSI,the width of the interference signal becomes larger along the scanning direction and its amplitude becomes smaller.Therefore a compensation glass(CG)is required to reduce the dispersion effect,and at the same time some technique is required to get exact scanning positions during a long scanning distance of a few millimeter.In this thesis,the thickness of glass plate with a few millimeter thickness was measured by using this method.In SRI,the interference signal distributed along wavenumber is almost equal to a sinusoidal waveform whose period is inversely proportional to the thickness of the glass plate or an optical path difference(OPD).And deviation from a sinusoidal waveform depends on the dispersion effect of the glass plate.A spectral analyzer with a high resolution is required to detect the complicated interference signals.Therefore a method is proposed to measure a large thickness of a glass plat by using a spectral analyzer with a low resolution.In this thesis,the theory of a SRI and WLSI are described and the characteristics of the interferometer are made clear through experiments.The specific research contents of this thesis are listed as follows:(1)The relationship between the dispersion contained in the white light interference signal and the thickness of the glass plate is illustrated.For eliminating the dispersion effect,a compensation material of the nearly same size and thickness was introduced in the reference arm to eliminate the dispersion effect.(2)The influence of the non-uniform motion of the piezoelectric transducer stage on the distribution of white light scanning interference signal is discussed.The actual position information of the white light interference signal is obtained by processing the monochromatic light signal,thus the measurement accuracy is improved.(3)A white-light scanning interferometer is constructed to detect the thickness and surface profile of a large-thickness object.The basic devices are placing two reference mirrors in the object arm and the reference arm,respectively.The reference mirror in the sample arm is scanned by moving the reference mirror inside the reference arm to complete the measurement of the surface profile and the thickness of the object.(4)A spectral resolved interferometer is proposed to measure the thickness of the object,and the thickness of the glass below 1mm can be measured directly with this method.The measurement of the 5mm thickness glass plate was realized by changing the measuring steps and adding the compensation glass plate in the reference arm.