利用雙波長相移干涉術量測三維表面輪廓

Abstract

本論文目的在擴展單波長相移干涉術對於縱向深度測量範圍。我們結合相移干涉術和雙波長干涉術，得一較長的等價波長，並將兩種不同波長量測出的相位值相減，使得量測表面輪廓的偵測器相鄰像素必須小於四分之一波長的限制得以擴展。 我們架設Fizeau式相移干涉顯微鏡，採用氦氖雷射波長632.8nm和氬離子雷射波長514.5nm為光源，得一較長的等價波長2752.1nm。利用電腦控制PZT推動參考面產生五步相移，並採用Hariharan相移干涉術演算法，及相位重建技術來求解初始相位差。 雙波長相移干涉術所得之結果其雜訊大於單波長相移干涉術的量測，可利用雙波長相移干涉術的計算為參考來校正單波長相移干涉術量測產生的2π相位混淆， 最後以單波長相移干涉術經校正的結果來重建表面輪廓。我們分別量測光柵和四階Fresnel偏轉鏡。

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.