• 제목/요약/키워드: interferometer

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Accurate Roughness Measurement Using a Method for Evaluation and Interpolation of the Validity of Height Data from a Scanning White-light Interferometer

  • Kim, Namyoon;Lee, Seung Woo;I, Yongjun;Pahk, Heui-Jae
    • Current Optics and Photonics
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    • v.1 no.6
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    • pp.604-612
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    • 2017

  • An effective and precise method using a scanning white-light interferometer (SWLI) for three-dimensional surface measurements, in particular for roughness measurements, has been proposed. The measurement of a microscopically sloped area using an interferometer has limitations, due to the numerical aperture of the lens. In particular, for roughness measurements, it is challenging to obtain accurate height data for a sloped area using the interferometer, due to diffraction of the light. Owing to these optical limitations of the interferometer for roughness measurements, the Ra measurements performed using an interferometer contain errors. To overcome the limitations, we propose a method consisting of the following two steps. First, we evaluate the height data and set the invalid height area to be blank, using the characteristics of the modulus peak, which has a low peak value for signals that have low reliability in the interferogram. Next, we interpolate the blank area using the adjacent reliable area. Rubert roughness standards are used to verify the proposed method. The results obtained by the proposed method are compared to those obtained with a stylus profilometer. For the considered sinusoidal samples, Ra ranges from $0.053{\mu}m$ to $6.303{\mu}m$, and we show that the interpolation method is effective. In addition, the method can be applied to a random surface where Ra ranges from $0.011{\mu}m$ to $0.164{\mu}m$. We show that the roughness results obtained using the proposed method agree well with profilometer results. The $R^2$ values for both sinusoidal and random samples are greater than 0.995.

  • https://doi.org/10.3807/COPP.2017.1.6.604 인용 PDF KSCI

Error analysis and performance test of the volumetric interferometer for three dimensional coordinate measurements (삼차원 좌표 측정을 위한 부피 간섭계의 오차분석 및 성능평가)

  • 이혁교;주지영;김승우
    • Korean Journal of Optics and Photonics
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    • v.13 no.6
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    • pp.521-529
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    • 2002

  • We have recently proposed the new concept of a phase-measuring volumetric interferometer that enables us to accurately measure the xyz-coordinates of the probe without metrology frames. The interferometer is composed of a movable target and a fixed photo-detector array. The target is made of point diffraction sources to emit two spherical wavefronts, whose interference is monitored by an array of photo-detectors. Phase shifting is applied to obtain the precise phase values of the photo-detectors. Then the measured phases are fitted to a geometric model of multilateration so as to determine the xyz-location of the target by minimizing least square errors. The proposed interferometer has been designed and built with a volumetric uncertainty of less than 1.0 $\mu\textrm{m}$ within a cubic working volume of side 120 mm. Here, in this paper, we also present error sources, an evaluated uncertainty, and test results from the prototype system. The self-calibration of two-dimensional precision metrology stages is applied to test the performance of the interferometer.

  • https://doi.org/10.3807/KJOP.2002.13.6.521 인용 PDF KSCI

Non-contact Detection of Ultrasonic Waves Using Fiber Optic Sagnac Interferometer (광섬유 Sagnac 간섭계를 이용한 초음파의 비접촉식 감지)

  • Lee, Jeong-Ju;Jang, Tae-Seong;Lee, Seung-Seok;Kim, Yeong-Gil;Gwon, Il-Beom;Lee, Wang-Ju
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.9
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    • pp.1400-1409
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    • 2001

  • This paper describes a fiber optic sensor suitable for non-contact detection of ultrasonic waves. This sensor is based on a fiber optic Sagnac interferometer. Quadrature phase bias between two interfering laser beams in Sagnac loop is introduced by a polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output versus phase bias. This method eliminates a digital signal processing for detection of ultrasonic waves using Sagnac interferometer. Interference intensity is affected by the frequency of ultrasonic waves and the time delay of Sagnac loop. Collimator is attached to the end of the probing fiber to focus the light beam onto the specimen surface and to collect the reflected light back into the fiber probe. Ultrasonic waves produced by conventional ultrasonic transducers are detected. This fiber optic sensor based on Sagnac interferometer is very effective for detection of small displacement with high frequency such as ultrasonic waves used in conventional non-destructive testing.

  • https://doi.org/10.22634/KSME-A.2001.25.9.1400 인용 PDF

Improvement of the Laser Interferometer Error in the Positioning Accuracy Measurement (레이저간섭계의 위치결정정밀도 측정오차 개선)

  • 황주호;박천홍;이찬홍;김승우
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.9
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    • pp.167-173
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    • 2004

  • The heterodyne He-Ne laser interferometer is the most widely used sensing unit to measure the position error. It measures the positioning error from the displacement of a moving reflector in terms of the wave length. But, the wave length is affected by the variation of atmospheric temperature. Temperature variation of 1$^\circ C$ results in the measuring error of 1ppm. In this paper, for measuring more accurately the position error of the ultra precision stage, the refractive index compensation method is introduced. The wave length of the laser interferometer is compensated using the simultaneously measured room temperature variations in the method. In order to investigate the limit of compensation, the stationary test against two fixed reflectors mounted on the zerodur$\circledR$ plate is performed firstly. From the experiment, it is confirmed that the measuring error of the laser interferometer can be improved from 0.34${\mu}m$ to 0.11${\mu}m$ by the application of the method. Secondly, for the verification of the compensating effect, it is applied to estimate the positioning accuracy of an ultra precision aerostatic stage. Two times of the refractive index compensation are performed to acquire the positioning error of the stage from the initially measured data, that is, to the initially measured positioning error and to the measured positioning error profile after the NC compensation. Although the positioning error of an aerostatic stage cannot be clarified perfectly, it is known that by the compensation method, the measuring error by the laser interferometer can be improved to within 0.1${\mu}m$.

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