Chih-Jen Yu

High speed interferometric ellipsometer

A novel high speed interferometric ellipsometer (HSIE) is proposed and demonstrated. It is based on a novel differential-phase decoder which is able to convert the phase modulation into amplitude modulation in a polarized heterodyne interferometer. Not only high detection sensitivity but also fast response ability on ellipsometric parameters (EP) measurements based on amplitude-sensitive method is constructed whereas different amplitudes with respect to P and S polarized heterodyne signals in this phase to amplitude modulation conversion is discussed. The ability of HSIE was verified by testing a quarter wave plate while a real time differential-phase detection of a liquid crystal device versus applied voltage by using HSIE was demonstrated too. These results confirm that HSIE is able to characterize the optical property of specimen in terms of EP at high speed and high detection sensitivity experimentally.

Paired circularly polarized heterodyne ellipsometer

We develop a paired circularly polarized heterodyne ellipsometer (PCPHE), in which a heterodyne interferometer based on a two-frequency circularly polarized laser beam is set up. It belongs to an amplitude-sensitive ellipsometer that is able to provide not only a wider dynamic range of polarization modulation frequency but also a higher detection sensitivity than that of a conventional photometric ellipsometer. A real-time and precise measurement of ellipsometric parameters, which demonstrated an accuracy of less than 1 nm on thickness measurement of SiO(2) thin film deposited on silicon substrate, can be applied with the PCPHE.

Kinetics of Glucose Mutarotation Assessed by an Equal-Amplitude Paired Polarized Heterodyne Polarimeter

A dual-frequency equal-amplitude paired polarization heterodyne polarimeter (DEPHP) was set up in order to precisely measure the mutarotation rate constants of D-glucose in tridistilled water. The DEPHP is based on a balanced detector detection scheme for measurement of the optical rotation angle of D-glucose/water solution during the conversion process between alpha-D-glucose and beta-D-glucose while in a nonequilibrium state. The DEPHP can perform shot-noise-limited detection, so that the total optical rotation angle together with the mutarotation rate constants of alpha-D-glucose and beta-D-glucose conversion can be measured with high sensitivity. In this experiment, the sensitivity of the optical rotation angle measurement was 8.3 x 10(-5) deg/cm, while the total (k), forward (k(1)) and reverse (k(2)) mutarotation rate constants of D-glucose were found to be k = 7.67 x 10(-5) s(-1), k(1) = 2.76 x 10(-5) s(-1), and k(2) = 4.91 x 10(-5) s(-1), respectively, in tridistilled water. Moreover, using the DEPHP, we can measure the specific rotation angles of alpha-D-glucose and beta-D-glucose in water at 632.8 nm. They were 105 degrees and 12 degrees, respectively. Finally, the detection sensitivity of the DEPHP system is also discussed.

Dual-frequency heterodyne ellipsometer for characterizing generalized elliptically birefringent media

This research proposed a dual-frequency heterodyne ellipsometer (DHE) in which a dual-frequency collinearly polarized laser beam with equal amplitude and zero phase difference between p- and s-polarizations is setup. It is based on the polarizer-sample-analyzer, PSA configuration of the conventional ellipsometer. DHE enables to characterize a generalized elliptical phase retarder by treating it as the combination of a linear phase retarder and a polarization rotator. The method for measuring elliptical birefringence of an elliptical phase retarder based on the equivalence theorem of an unitary optical system was derived and the experimental verification by use of DHE was demonstrated too. The experimental results show the capability of DHE on characterization of a generalized phase retardation plate accurately.

High sensitivity two-frequency paired polarized interferometer in Faraday rotation angle measurement of ambient air with single-traveling configuration

High sensitivity detection on Faraday rotation and Verdet constant of ambient air under weak applied magnet field and single-pass configuration specimen is setup in which a two-frequency paired linear polarized interferometer (TPPI) coupled with balanced detector shown at shot-noise-limited detection is demonstrated. The Verdet constant of ambient air at 1.3×10−6 rad/mT m and its sensitivity at 4.3×10−8 rad/mT m were measured. Additionally, this method also is able to extend into a broad spectral range on Faraday rotation angle or Verdet constant measurement. Finally, the enhancement on detection sensitivity by integrating a Fabry–Perot cavity into TPPI is discussed.

Characterization of a nematic PALC at large oblique incidence angles

Compared with conventional photometric methods of measuring cell parameters, including the cell gap and the pretilt angle of a nematic parallel-aligned liquid crystal (PALC) using multiple wavelengths at normal incidence, this research proposes the use of a phase-sensitive interferometric ellipsometer to determine cell parameters precisely based on a single wavelength at large oblique incidence angles. The advantage of this method is that it detects the phase difference using an optical heterodyne interferometer in which a common phase noise rejection mode is provided. Thus, there is a high signal-to-noise ratio (SNR) on the phase measurement. In addition, a range of large oblique incidence angles on the PALC is used so that a high sensitivity measurement of the cell parameters is obtained experimentally. During the measurements, the multiple reflections and spatial shifting effect of the emerging extraordinary ray (E-ray) and ordinary ray (O-ray) from the PALC at large oblique incidence angles are able to be reduced effectively by the use of retro-reflected geometry in the interferometer. The experimental results verify that the sensitivities for the cell gap and pretilt angle measurements are 0.3 nm and 0.01 degrees , respectively.

Heterodyne Linear Polarization Modulation Ellipsometer

In this study, a novel heterodyne linear polarization modulation ellipsometer (LPME) is developed. It is based on a linear polarization rotator and is integrated with a common path heterodyne interferometer for ellipsometric parameter measurement. LPME is an amplitude-sensitive interferometric ellipsometer that can not only provide a wider range for its polarization modulation frequency than that of a conventional photometric ellipsometer but also be used for measurement in real time. LPME is also insensitive to laser intensity fluctuations. The independence of the elliptical polarization to the incident laser beam induced by imperfections in the quarter-wave plate in LPME is analyzed.

Degrees of polarization and coherence of paired linear polarized laser beam by scattering glass plates measured using optical coherent ellipsometer

An accurate optical coherent ellipsometer (OCE) is proposed and setup in which a two-frequency paired linear polarized laser beam is integrated with a common-path heterodyne interferometer. This OCE is able to precisely measure the optical properties of scattering specimen by measuring ellipsometric parameters (Psi, Delta). In the mean time the degree of polarization P, and degree of coherence Chi of incident two-frequency linear polarized laser beam are measured too. In the experiment, both smooth and ground BK7 glass plates were tested in which the optical parameters (Psi, Delta, P, Chi ) were obtained precisely. Comparing with conventional ellipsometers, OCE can characterize scattering specimen precisely and excludes the scattering effect.

Two-Frequency Paired Polarization Interferometer for Faraday Rotation Angle Detection

A highly sensitive two-frequency paired linear polarized interferometer (TPPI) for measuring the Faraday rotation angle and Verdet constant of the Bi12SiO20 (BSO) crystal in real time was set up by an amplitude-sensitive detection method. TPPI features a common-path heterodyne interferometer in conjunction with a highly correlated paired linear polarized laser beam. Then, the antisymmetry of polarized heterodyne signals is produced and Faraday rotation angle detection by a balanced detector scheme is satisfied automatically. As a result, shot-noise-limited detection of Faraday rotation angle is possible. In addition, the Faraday rotation angle detection is also insensitive to the scattering and absorption caused by the specimen because of the common-path propagation of the paired linear polarized laser beam. Experimentally, the sensitivities of Faraday rotation angle and Verdet constant measurements of the BSO crystal under the arrangement with a single pass of the laser beam in TPPI are 4.93×10-5 rad/mm and 2.6×10-7 rad/(mTmm), respectively. This suggests that the Faraday rotation angle detection sensitivity has the potential to be on the order of 10-8 rad/mm if a Fabry–Perot cavity with a finesse of F=120 is used in TPPI.

Alpha-fetoprotein Detection by Using a Localized Surface Plasmon Coupled Fluorescence Fiber-Optic Biosensor

Alpha-fetoprotein (AFP) detection by using a localized surface plasmon coupled fluorescence (LSPCF) fiber-optic biosensor is setup and experimentally demonstrated. It is based on gold nanoparticle (GNP) and coupled with localized surface plasmon wave on the surface of GNP. In this experiment, the fluorophores are labeled on anti-AFP which are bound to protein A conjugated GNP. Thus, LSPCF is excited with high efficiency in the near field of localized surface plasmon wave. Therefore, not only the sensitivity of LSPCF biosensor is enhanced but also the specific selectivity of AFP is improved. Experimentally, the ability of real time measurement in the range of AFP concentration from 0.1ng/ml to 100ng/ml was detected. To compare with conventional methods such as enzyme-linked immunosorbent assay (ELISA) or radioimmunoassay (RIA), the LSPCF fiber-optic biosensor performs higher or comparable detection sensitivity, respectively.