| Summary: | 碩士 === 國立交通大學 === 光電工程所 === 87 === In this thesis, our purpose is to improve the measurement limitation of the vertical depth in single-wavelength phase-shifting interferometry (PSI), in which the depth difference between adjacent pixels is required to be less than a quarter of wavelength. We combine the PSI with two-wavelength interferometry, in which two different wavelengths are used in the measurement. By subtraction of the two phases measured at two different wavelengths, we can get the surface profile at a much longer equivalent wavelength.
A Fizeau type phase-shifting interference microscope was set up. Instead of single wavelength, we used two wavelengths, of which is 514.5nm from an argon-ion laser and the other is 632.8nm from a He-Ne laser. In this way, we have an equivalent wavelength of 2752.1nm, which is much longer than either single wavelength. A five-step phase shift was executed by moving the reference surface, driven by a computer-controlled PZT. Hariharan PSI algorithm and phase unwrapping technique were used to reconstruct the measured 3-D surface profile.
Since the noise of the data measured by the two-wavelength PSI was much larger than that measured by the single-wavelength PSI. We only used the results from two-wavelength PSI as reference to correct 2πphase ambiguity in the unwrapping of the single-wavelength PSI data, and reconstructed the surface profile with the single-wavelength PSI data. As examples, we measured a grating and a four-level Fresnel deflector.
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