雙波長光彈調變式橢圓偏光儀及波形量測法

Abstract

一個(週期)波形紀錄了一個資訊，只要能將波形儲存下來，我們就可以得知樣品在某時間點的狀態。因為數據擷取卡可以將光彈調變式橢圓偏光儀的波形數量化並記錄，因此我們可以藉由DAQ卡紀錄訊號波形之後再加以分析來推測當時樣品發生的狀況，我們稱此法為波形量測法，此法可以量到很短時間發生的事件並記錄所有資訊。在反射式的光彈調變式橢圓偏光儀的架構下以一標準SiO2/Si薄膜當作樣本，我們將所存的波形採傅立葉轉換的方法並推算出橢圓偏光參數 和 ，其結果可以與NI所發行的虛擬鎖相放大器所量出的結果相匹配。藉由兩個週期的分析，我們可以一秒鐘內量測到25000組偏光參數，大大的提高了量測速度。以此法我們可將交替雙波長(488, 632.8 nm)量測法實現。此結果可以作為將來用LabVIEW 頻譜分析儀來實現雙波長即時量測的參考。我們並拿液晶加週期性方波電壓當作動態樣本，來測試此法對動態樣本量測的可行性。另一方面，我們發現輸出訊號的波形會隨著不同電壓及波長做特定的變動。將來可以藉由對波形在時域上的分析，就可以得知道樣品的資訊。

For increasing the speed of measurement, we propose to record the waveform then analyze it afterward, namely post flight analysis (PFA) technique. The waveform in a photoelastic modulator ellipsometric system can be digitized by the Data Acquisition system (DAQ), so it is suitable for this PFA technique. We successfully Fourier transformed the waveform measured in the photoelastic modulation (PEM) ellipsometry, which was set to study a SiO2/Si thin film. The results are comparable with those measured by the NI virtual Lockin Amplifier. Taking two cycles for analyzing, we can speed up the PEM ellipsometry by a factor of 25000. A two wavelengths ellipsometry is set up for measuring the ellipsometric parameters and of SiO2/Si thin film, but the phase is fixed at 0.383 under the wavelength of 568.2 nm. Beside the ellipsometric parameters of the static sample, we also measured a dynamic sample-liquid crystal to demonstrate the ability of the technique. In addition, we also like to introduce a simple phase analysis in the time domain. The accuracy of these two techniques are still under study.