光彈調變器之線上校正及橢圓偏光參數量測

Abstract

本文主要是校正光彈調變式橢圓偏光儀中的光彈調變器，又由於光彈調變器也可用在偏光儀上，故在此提出一個不需改變任何裝置的線上校正法。 本法是利用數據擷取卡量取光彈調變器之多倍頻信號，進而換算光彈調變器的相位調變振幅及其內稟相位延遲。 利用多倍頻信號比我們量出光彈調變器的相位調變振幅偏移了 0.020□，此偏差並且可以用其數據化之檢波波形加以應證。 本研究並證明數據化之檢波波形的不對稱也因為光彈調變器的內稟相位延遲的存在。 在相位調變振幅及其內稟相位延遲校正後所量出的橢圓偏光參數與商用橢圓偏光儀的量測結果吻合。 為延伸此儀器為一多波長的橢圓偏光儀，在固定調變相位延遲下以568.2nm為中心波長，進行五個不同波長光彈調變器的相位調變振幅校正和橢圓偏光參數量測，其結果亦和理論值吻合。 最後在光彈調變橢圓儀系統加入分割器，證實系統每秒可取十點的橢圓偏光參數Δ和Ψ值，大幅提升橢圓儀的準確性與方便性。

The photoelastic modulator (PEM) can be used in polarimetric and ellipsometric system for real time/in situ measurements; therefore, we proposed an in situ calibration technique for PEM. This calibration technique is achieved by using the multiple harmonic intensity ratios (MHIR), which are obtained from the Fourier analysis of a data acquisition system (DAQ). One can calculate the phase modulation amplitude and static phase retardation of PEM by MHIR. In this study, we find that the phase modulation amplitudes are almost parallel shifted from its displayed value by 0.020□. The digitized oscilloscope waveform measured in the transmission style is used to confirm our measurements. In addition to the phase modulation amplitude of PEM, we also confirm the unsymmetrical oscilloscope waveform is caused by the intrinsic static phase retardation of PEM itself. The measured ellipsometric parameters of a standard thin film are consistent with that measured by a commercial ellipsometer, after calibrating the phase modulation amplitude and static phase retardation. In order to develop a spectroscopic-polarimeter /ellipsometer, we determine the phase modulation amplitude and its static retardation under varies wavelength at a fixed modulation amplitude for its centered wave (i.e.0.383□, where □= 568 nm) by a multi-wavelength tunable laser. These measurements are consistent with our theoretical prediction. Finally, we added a chopper to our system and proved that one can obtain ten pairs ellipsometric parameters in a second from our PEM ellipsometry.