A novel balanced detector interferometric ellipsometer (BDIE), composed of a polarized common-path optical heterodyne interferometer incorporating a novel balanced detector, provides an amplitude-sensitive method for measurement of the elliptical parameters of a thin film. The requirement for equal amplitude of the polarized heterodyne signals for balanced detection results in the simultaneous measurement of the elliptical parameters in terms of the azimuth angle of a half-wave plate and the output intensity from the differential amplifier, respectively. The common-path feature of BDIE shows a common phase noise rejection mode and this enhances the sensitivity of the phase measurement. At the same time, the balanced detector configuration of BDIE reduces excess noise of laser intensity fluctuation to give better sensitivity during measurement. The error of measurement of BDIE is derived and analyzed. Finally, the elliptical polarization effect of the laser beam is found to be independent of the measurement of the elliptical parameters.
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