Browsing by Author "Chao, YF"

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A direct determination technique for azimuth alignment in photoelastic modulation ellipsometry
(1999-12-01)
Chao, YF
;
Wang, CK
;
Liu, S
;
光電工程學系
;
Department of Photonics
Instead of the nulling method, a three-intensity-measurement technique is proposed to determine the azimuth deviation of the polarizer (P), photoelastic modulator (PEM) and analyzer (A) with respect to the specimen surface for ellipsometric measurements. After the initial alignment in a straight-through setup, we adjusted the azimuth of P at 45 degrees to the strain axis of the PEM. Arranging a Polarizer-PEM-Sample-Analyzer ellipsometer by subjecting a specimen at the required incident angle, we measured a set of three DC radiances at the zero point of the zero-order Bessel function. In addition to the azimuth deviation, the ellipsometric parameter can also be determined from the same measurements.
A three-intensity technique for polarizer-sample-analyser photometric ellipsometry and polarimetry
(1998-08-21)
Chao, YF
;
Lee, WC
;
Hung, CS
;
Lin, JJ
;
交大名義發表
This work presents a novel three-intensity-measurement technique to determine the ellipsometric parameters psi and Delta in a polarizer-sample-analyser photometric ellipsometer. This technique can be employed to correct the azimuthal misalignment of the analyser with respect to the plane of incidence. By performing two sets of measurements with this technique with the polarizer's azimuth at +45 degrees and -45 degrees, respectively, we can simultaneously determine the azimuthal deviation of the polarizer and further improve the ellipsometric measurements. Applying this technique in the transmission mode allows us to obtain the phase retardation and the optical axis of a waveplate at the same time.
An error evaluation technique for the angle of incidence in a rotating element ellipsometer using a quartz crystal
(1999-09-07)
Chao, YF
;
Wang, MW
;
Ko, ZC
;
交大名義發表
;
National Chiao Tung University
The error in the angle of incidence for a rotating element ellipsometer is evaluated using a uniaxial quartz crystal. At a fixed angle of incidence with respect to the surface of reflection, the ratio of reflectance in the parallel to that in the perpendicular electromagnetic field is measured by rotating the quartz crystal through a full cycle. We determine the deviation in the angle of incidence by comparing: the experimentally measured reflectance ratio to its calculated value.
Analytical solutions of the azimuthal deviation of a polarizer and an analyzer by polarizer-sample-analyzer ellipsometry
(2006-06-10)
Chao, YF
;
Lee, KY
;
Lin, YD
;
光電工程學系
;
Department of Photonics
The analytical solutions of the azimuthal deviation of a polarizer and an analyzer were obtained by polarizer-sample-analyzer ellipsometry with a three-intensity measurement technique. By performing two sets of this three-intensity measurement with the polarizer's azimuth set at 45 degrees and at -45 degrees, we were able to obtain a set of ellipsometric parameters free from the azimuthal deviations of the polarizer and the analyzer. (c) 2006 Optical Society of America.
Azimuth alignment in photoelastic modulation ellipsometry at a fixed incident angle
(2002-06-01)
Wang, MW
;
Chao, YF
;
光電工程學系
;
Department of Photonics
A high intensity ratio technique is proposed to align all the azimuthal angles of a photoelastic modulation ellipsometric system in a fixed incident angle. This technique is used to determine the azimuthal orientations of the polarizer, the photoelastic modulator and the analyzer to the incident plane, Two pre-designed testing samples and two probing wavelengths for a thin film are introduced to locate the incident plane by the intensity ratio technique in a polarizer-sample-analyzer ellipsometric setup. Then, the azimuth of the pholoelastic modulator is directly obtained from two DC radiances separated by 45degrees. In addition to azimuth deviation, the ellipsometric parameter psi can also be determined from the same measurement for determining the incident angle on-line.
Calibrations of phase modulation amplitude of photoelastic modulator
(2004-02-01)
Wang, MW
;
Chao, YF
;
Leou, KC
;
Tsai, FH
;
Lin, TL
A multiple harmonic intensity ratio technique is proposed for calibrating the modulation amplitude (Delta(0)) of a photoelastic modulator (PEM). A data acquisition system is utilized to investigate the frequency response of this technique. Delta(0) determined by this technique is independent of frequency, which is proved using the reflection and transmission setups. In addition to confirm our calibration using the digitized oscilloscope waveform, we also obtain a set of ellipsometric parameters under various values of Delta(0) before and after calibration. We also introduce a correction factor to correct the effect caused by the shift of the modulation amplitude in the process of etching. An optical thick film is used to calibrate Delta(0) using PEM ellipsometry, and its refractive index and extinction coefficient are also obtained in etching. Finally, we suggest the use of the traces of the ellipsometric parameters under various thicknesses for monitoring instead of calculating the thickness in real time.
Determination of optical parameters of a twisted-nematic liquid crystal by phase-sensitive optical heterodyne interferometric ellipsometry
(2005-12-10)
Tsai, CC
;
Chou, C
;
Han, CY
;
Hsieh, CH
;
Liao, KY
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. (c) 2005 Optical Society of America.
Direct determination of azimuth angles in photoelastic modulator system
(1998-06-01)
Chao, YF
;
Wang, CK
;
光電工程學系
;
Department of Photonics
Instead of the nulling method, a high-level intensity technique is proposed to determine the relative azimuth orientation of a photoelastic modulator and an analyzer. In a photoelastic modulating system, one can obtain a DC intensity distribution by varying the phase modulation amplitude at two azimuth angles of the analyzer, which are pi/4 apart from each other. The relative azimuth orientation can be determined by taking the ratio of the slopes of these two intensity distributions around the linear region of the zero point of the zero-order Bessel function. A similar technique is also applicable to wave plates for aligning their optical axes with the system.
In situ calibration technique for photoelastic modulator in ellipsometry
(2004-05-01)
Wang, MW
;
Tsai, FH
;
Chao, YF
;
光電工程學系
;
Department of Photonics
The modulation amplitude of a phase modulator is calibrated under a fixed incident angle in photoelastic modulation (PEM) ellipsometry. In addition to its modulation amplitude (Delta(o)), we also calibrated its static phase retardation at 632.8 nm. The ellipsometric parameters of a sample were measured by a multiple harmonic intensity ratio technique and proved that ellipsometric parameters can be obtained under various modulation amplitudes. Since the physical size of PEM is constant, we calibrated the modulation amplitude at multiple wavelengths by setting the Delta(o) value at 0.383 for 568.2 nm. These calibrations provided enough information for establishing an in situ/real time spectroscopic ellipsometry. (C) 2003 Elsevier B.V. All rights reserved.
Index profile of radial gradient index lens measured by imaging ellipsometric technique
(2005-02-01)
Chao, YF
;
Lee, KY
;
光電工程學系
;
Department of Photonics
A simple three-intensity imaging ellipsometric technique is proposed for measurement of the refractive index profile (RIP) of a radial gradient index (GRIN) lens. According to our numerical analysis, the improved ellipsometric parameters measured by this method are valid as long as the azimuth deviation of the polarizer is less than 3 degrees. A BK7 glass and a radial GRIN lens were measured. A fairly flat refractive index surface profile was obtained for the glass within a 0.3% error. The on-axis refractive index of the radial GRIN lens and its RIP are well fitted to the specifications provided by the manufacturer. Instead of the refracted-ray method, we provide a reflective and nondestructive measurement technique for measurement of the gradient index of a flat surface.
Measurement of optical activity using a photoelastic modulator system
(1999-02-01)
Wang, CK
;
Chao, YF
;
光電工程學系
;
Department of Photonics
Adjusting the analyzer at 90 degrees to the strain axis of a photoelastic modulator, one can determine the optical activity by measuring the slope of its DC intensity distribution under various phase modulation amplitudes. This technique was applied to measure the ellipticity of few quartz quarter-wave plates and the optical rotation of an optical active crystal. A multiple reflection enhancement effect in the wave prate was observed and discussed. By considering the photoelastic modulator as an elliptical retarder, we also determined its intrinsic ellipticity and static phase retardation, to increase the accuracy of measurements.
Photoelastic modulated imaging ellipsometry by stroboscopic illumination technique
(2006-02-01)
Han, CY
;
Chao, YF
;
光電工程學系
;
Department of Photonics
A novel stroboscopic illumination technique is applied in a photoelastic modulated (PEM) ellipsometry to conquer the slow imaging processing of charge-coupled device camera system and form a fast imaging ellipsometry. The synchronized ultrastable short pulse is used to freeze the intensity variation of the PEM modulated signal. The temporal phase is calibrated with respect to the time reference of PEM. The laser diode is modulated by a programable pulse generator for triggering four short pulses at their specific temporal phase angle. The two-dimensional (2D) ellipsometric parameters can be deduced from those recorded four images. Therefore, the 2D thickness profile of a patterned sample can be measured; a static patterned SiO2 thin film on silicon substrate and the drainage behavior of matching oil on silicon wafer were studied by this imaging ellipsometry. (c) 2006 American Institute of Physics.
Photoelastic modulation polarimetry and its measurement of twisted nematic liquid crystal
(2001)
Chao, YF
;
Lin, A
;
Wang, MW
;
光電工程學系
;
Department of Photonics
For in situ/real time measurement, a retarder is substituted by a photoelastic modulator (PEM) in a polarimetry. The azimuthal position of the strain axis of PEM is directly determined with respect to the orientation of the transmission axis of polarizer and analyzer. The Mueller matrix of a twisted nematic liquid crystal (TN-LCD) is derived analytically. The phase retardation and the twisted angle of a TN-LCD are numerically obtained through two successive measurements of the Mueller polarimeter.
The ellipsometric measurements of a curved surface
(2005)
Lee, KY
;
Chao, YF
;
光電工程學系
;
Department of Photonics
A three-intensity imaging ellipsometric technique is proposed to investigate the surface topography as well as the refractive index profile (RIP) of a lens. The azimuth deviation of polarizer caused by the tilting of a SiO2 thin film on Si substrate was investigated after a careful calibration on the azimuth position of polarizer of the water-surface. The azimuth deviation of polarizer is proved to be the local surface normal; thus we can determine not only the radius of curvature of a Plano-Convex lens from the measurement, but also its incident-angle-corrected RIP.
The intensity ratio alignment technique in photoelastic modulation ellipsometry and polarimetry
(2002)
Chao, YF
;
光電工程學系
;
Department of Photonics
The concept of intensity ratio alignment technique will be introduced by comparing it with the conventional null technique. For in situ/real time monitoring the plasma etching process, we will introduce a fixed incident angle alignment technique for a photoelastic modulation ellipsometer. In addition to ellipsometry, we will introduce a photoelastic modulation polarimetry to measure the twisted angle and phase retardation of a twisted nematic liquid.
Ultra-fast surface plasmon resonance biological detection by means of photoelastic modulated ellipsometry
(2004)
Han, CY
;
Chao, YF
;
Lee, CL
;
光電工程學系
;
Department of Photonics
A photoelastic modulated ellipsometry combined with SPR technique is proposed. In addition to monitor the biological interactions in real time, we also installed a post flight analysis technique to analyze the same system synchronously.