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To be compared with the wavelength modulation technique for measuring two-dimensional (2D) cell parameters of a twisted nematic liquid crystal (TN-LC), we propose an amplitude-sensitive heterodyne ellipsometer (ASHE) of a single wavelength that is able to characterize TN-LC in 2D quantitatively. A quarter-wave plate (QWP) is rotated continuously in this setup to modulate the polarization state of the incident laser beam to obtain the amplitude ratio of the S and P waves versus the rotation angle of the QWP. Thus the cell parameters, including the twisted angle [PHI], untwisted phase retardation [GAMMA], rubbing direction angle [alpha], and cell gap d, of a TN-LC cell are obtained simultaneously by best fitting the detected amplitude ratio with a prediction based on the transfer matrix of TN-LC cell. 2D distributions of ([PHI], [GAMMA]. [alpha], d) are then obtained either by scanning the TN-LC cell or by using a CCD camera for high-speed measurement. In this experiment, the stability of the amplitude-ratio measurement of the proposed ASHE was 0.5%. The goal is to integrate the rotating elliptical wave plate with the TN-LC cell in a heterodyne ellipsometer to obtain cell parameters at amplitude sensitivity. This increases not only the sensitivity of the measurement but also the possibility of extending the 2D distribution of cell parameters in real time. OCIS codes: 120.3180, 120.2130, 040.2840.

To characterize the linear birefringence of a multiple-order wave plate (MWP), an oblique incidence is one of the methods available. Multiple reflections in the MWP are produced, and oscillations in the phase retardation measurement versus the oblique incident angle are then measured. Therefore, an antireflection coated MWP is required to avoid oscillation of the phase retardation measurement. In this study, we set up a phase-sensitive heterodyne ellipsometer to measure the phase retardations of an uncoated MWP versus the oblique incident angle, which was scanned in the x-z plane and y-z plane independently. Thus, the effect on multiple reflections by the MWP is reduced by means of subtracting the two measured phase retardations from each other. As a result, a highly sensitive and accurate measurement of retardation parameters (RPs), which includes the refractive indices of the extraordinary ray [n.sub.e] and ordinary ray no, is obtained by this method. On measurement, a sensitivity ([n.sub.e], [n.sub.o]) of [10.sup.-6] was achieved by this experiment setup. At the same time, the spatial shifting of the P and S waves emerging from the MWP introduced a deviation between experimental results and the theoretical calculation. OCIS codes: 120.3180, 040.2840, 120.5050, 120.5410.

What is believed to be a novel phase-sensitive optical heterodyne interferometric ellipsometer is set up to characterize a twisted-nematic liquid crystal (TN-LC) by the elliptical parameters of the output polarization state. This ellipsometer presents the advantages of both polarized optical heterodyne interferometry and optical photometry, which introduce a polarization modulation that is capable of performing with high-sensitivity on phase detection in real time. The twist angle [phi] and the untwisted phase retardation [GAMMA] of TN-LC are measured precisely. The experimental results verify that a TN-LC can be treated as identical to an elliptical retarder. OCIS codes: 120.2130, 120.3180, 120.5240, 120.5410, 160.3710.