2005 Fiscal Year Final Research Report Summary
Generation of a ruler marking every wavelength and its application to nano measurement by a wavelength-scanning interferometer with double feedback control
| Project/Area Number |
16560033
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied optics/Quantum optical engineering
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| Research Institution | Niigata University |
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Principal Investigator |
SASAKI Osami Niigata University, Institute of Science and Technology, Professor, 自然科学系, 教授 (90018911)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Takamasa Niigata University, Institute of Science and Technology, Associate Professor, 自然科学系, 助教授 (40206496)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Wavelength scanning / Laser interferometry / Tunable wavelength filter / Feedback Control / Phase lock / Distance measurement |
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| Research Abstract |
This research deals analyses and experiments about real-time measurement of a distance longer than a wavelength using sinusoidal wavelength-scanning (SWS) interferometer and double feedback control system. In addition to a conventional phase α an interference signal of SWS interferometer has phase-modulation amplitude Z_b that is proportional to the optical path difference (OPD) and amplitude b of the wavelength-scanning. Voltage applied to the PZT which gives a displacement to a reference mirror and makes the phase α equal to a constant value (2π or 3π/2) becomes a ruler with scales smaller than a wavelength. Voltage applied to a wavelength-scanning device that determines the amplitude b of the wavelength-scanning and makes the amplitude Z_b equal to π or 2π becomes a ruler marking every a wavelength. The calibration of the ruler marking every a wavelength could be made automatically with the double feedback control by changing the OPD at intervals of about a wavelength. These two rul
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ers enabled us to measure an absolute distance longer than a wavelength in real-time.
A liquid-crystal Fabry-Perot interferometer (LC-FPI) was adopted as a wavelength-scanning device in the SWS interferometer with double feedback control. By incorporating double sinusoidal phase-modulation we obtained a better interference signal from which we could generate the feedback signal whose frequency bandwidth was equal to twice the frequency of the SWS. Because of the high resolution of the LC-FPI in the SWS we could obtained the upper limit of the measurement range to 200 μm. Moreover we used the phase lock of Z_b=2π instead of Z_b=π, so that the upper limit of the measurement range became 300 μm. We obtained all of stable points from 100 μm to 300 μm, and we measured the relative distance around the OPD of 270 μm with a high accuracy of the order of nanometer. Moreover, an acousto-optical tunable wavelength filter (AOTF) was also adopted as a wavelength-scanning device. In this case the repeatability of the stable points was higher that in the case of the LC-FPI.
A linear CCD image sensor was used to electrically scan a measuring point and measure one-dimensional step-profiles in real-time with this interferometer. Two different step profiles with a step height of 1 μm and 20 μm, respectively, were measured with the measurement error less than 8 nm. Measuring time for one measuring point was 0.04 s. Less
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Research Products
(2 results)
