Browsing by Author "Wu, Wang-Tsung"

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Alternative method for measuring the full-field refractive index of a gradient-index lens with normal incidence heterodyne interferometry
(2010-12-20)
Chen, Yen-Liang
;
Hsieh, Hung-Chih
;
Wu, Wang-Tsung
;
Chang, Wei-Yao
;
Su, Der-Chin
A linearly/circularly polarized heterodyne light beam coming from a heterodyne light source with an electro-optic modulator in turn enters a modified Twyman-Green interferometer to measure the surface plane of a GRIN lens. Two groups of periodic sinusoidal segments recorded by a fast complementary metal-oxide semiconductor camera are modified, and their associated phases are derived with the unique technique. The data are substituted into the special equations derived from the Fresnel equations, and the refractive index can be obtained. When the processes are applied to other pixels, the full-field refractive-index distribution can be obtained similarly. Its validity is demonstrated. (C) 2010 Optical Society of America
An alternative bend-testing technique for a flexible indium tin oxide film
(2010-12-01)
Chen, Yen-Liang
;
Hsieh, Hung-Chih
;
Wu, Wang-Tsung
;
Wen, Bor-Jiunn
;
Chang, Wei-Yao
The two-dimensional refractive index distribution of a flexible indium tin oxide film deposited on a PET layer is measured before/after the bend-testing with an alternative technique based on Fresnel equations and the heterodyne interferometry. Their standard deviations are derived and they vary more obviously than the resistance variations measured in the conventional method. Hence the standard deviation of the refractive index can be used as the indicator to justify the durability of a flexible indium tin oxide film. The validity is demonstrated. (C) 2010 Elsevier B.V. All rights reserved.
Full-field refractive index distribution measurement of a gradient-index lens with heterodyne interferometry
(2010-10-01)
Hsieh, Hung-Chih
;
Chen, Yen-Liang
;
Wu, Wang-Tsung
;
Chang, Wei-Yao
;
Su, Der-Chin
A light beam coming from a circular heterodyne light source with an electro-optic modulator is incident on a gradient-index lens obliquely. The reflected light passes through an analyzer and an imaging lens, and is recorded by a fast CMOS camera. A group of periodic sinusoidal segments recorded by each pixel is modified, and its associated phase is derived with a unique technique. The processes are applied to other pixels; the two-dimensional phase distribution can be obtained similarly. The estimated data are substituted into the special equations derived from Fresnel's equations, and the full-field refractive index distribution of the gradient-index lens can be obtained. This method has the merits of both common-path interferometry and heterodyne interferometry.
Full-field refractive index distribution measurement of a gradient-index lens with heterodyne interferometry
(2010-10-01)
Hsieh, Hung-Chih
;
Chen, Yen-Liang
;
Wu, Wang-Tsung
;
Chang, Wei-Yao
;
Su, Der-Chin
A light beam coming from a circular heterodyne light source with an electro-optic modulator is incident on a gradient-index lens obliquely. The reflected light passes through an analyzer and an imaging lens, and is recorded by a fast CMOS camera. A group of periodic sinusoidal segments recorded by each pixel is modified, and its associated phase is derived with a unique technique. The processes are applied to other pixels; the two-dimensional phase distribution can be obtained similarly. The estimated data are substituted into the special equations derived from Fresnel's equations, and the full-field refractive index distribution of the gradient-index lens can be obtained. This method has the merits of both common-path interferometry and heterodyne interferometry.
High-accuracy thickness measurement of a transparent plate with the heterodyne central fringe identification technique
(2011-07-20)
Wu, Wang-Tsung
;
Hsieh, Hung-Chih
;
Chang, Wei-Yao
;
Chen, Yen-Liang
;
Su, Der-Chin
In a modified Twyman-Green interferometer, the optical path variation is measured with the heterodyne central fringe identification technique, as the light beam is focused by a displaced microscopic objective on the front/rear surface of the test transparent plate. The optical path length variation is then measured similarly after the test plate is removed. The geometrical thickness of the test plate can be calculated under the consideration of dispersion effect. This method has a wide measurable range and a high accuracy in the measurable range. (c) 2011 Optical Society of America
Method for gauge block measurement with the heterodyne central fringe identification technique
(2010-06-01)
Wu, Wang-Tsung
;
Chen, Yen-Liang
;
Hsieh, Hung-Chih
;
Chang, Wei-Yao
;
Su, Der-Chin
In a modified Michelson interferometer, the top face of the wringing platen is first identified using the heterodyne central fringe identification technique. Then the reference mirror located in the other arm is moved by a precision translation stage until the top face of the tested gauge block is also identified with the same technique. The displacement of the mirror is exactly equivalent to the length of the tested gauge block. The measurable range of the interferometer relates to the maximum travel range of the translation stage and its uncertainty depends on the uncertainty of the heterodyne central fringe identification method and the resolution of the translation stage. (C) 2010 Optical Society of America
Nano-roughness measurements with a modified Linnik microscope and the uses of full-field heterodyne interferometry
(2008-12-01)
Chen, Yen-Liang
;
Jian, Zhi-Cheng
;
Hsieh, Hung-Chih
;
Wu, Wang-Tsung
;
Su, Der-Chin
A collimated heterodyne light enters a modified Linnik microscope, and the full-field interference signals are taken by a fast CMOS camera. The sampling intensities recorded at each pixel are fitted to derive a sinusoidal signal, and its phase can be obtained. Next, the 2-D phase unwrapping technique is applied to derive the 2-D phase distribution. Then, Ingelstam's formula is used to calculate the height distribution. Last, the height distribution is filtered with the Gaussian filter, the roughness topography and its average roughness can be obtained and its validity is demonstrated. (c) 2008 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3050357]
Optimal sampling conditions for a commonly used charge-coupled device camera in the full-field heterodyne interferometry
(2011-04-01)
Hsieh, Hung-Chih
;
Wu, Wang-Tsung
;
Chang, Wei-Yao
;
Chen, Yen-Liang
;
Su, Der-Chin
The processes to derive the associated phase of an interference signal from the data of a series of recorded frames are performed, and we find that the sampling frequency being lower than the Nyquist sampling rate can also be applied to the full-field heterodyne interferometry. Two optimal sampling conditions for a commonly used CCD camera are proposed based on the relation between the heterodyne frequency and the contrast of the interference signal under the condition that the phase error is set to be 0.05 deg. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.356712]
Two-wavelength full-field heterodyne interferometric profilometry
(2009-02-01)
Hsieh, Hung-Chih
;
Chen, Yen-Liang
;
Jian, Zhi-Chen
;
Wu, Wang-Tsung
;
Su, Der-Chin
An alternative full-field interferometric profilometry is proposed by combining two-wavelength interferometry and heterodyne interferometry. A collimated heterodyne light is introduced into a modified Twyman-Green interferometer, the full-field interference signals are taken by a fast CMOS camera. The sampled intensities recorded by each pixel are fitted to derive a sinusoidal signal with the least-square sine wave fitting algorithm, and its phase can be obtained. Comparing the phase of the reference point, the relative phase of the pixel can be calculated. Next, the same measurement is made again at a different wavelength. The relative phase with respect to the effective wavelength can be calculated and the profile of the tested sample can be derived with the two-wavelength interferometric technique. Its validity is demonstrated. It has merits of both two-wavelength interferometry and heterodyne interferometry.