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횡자장하에서 633㎚ He - Ne 레이저의 주파수 안정화
엄태봉(Tae Bong Eom),박진원(Jin Won Park),정명세(Myung Sai Chung),양준묵(Joon Mook Yang) 한국광학회 1993 한국광학회지 Vol.4 No.4
횡자장하에서 Zeeman 분리된 두 편광성분의 맥놀이 주파수와 출력 차를 이용하여 내부 반사경형 633㎚ He-Ne 레이저의 주파수를 각각 안정화시켰다. 맥놀이 주파수를 이용할 경우 주파수안정도(square root Allan variance)와 주파수 온도계수는 7.0×10-¹¹ 과 170㎑/℃였으며, 출력차이를 이용할 경우에는 1.1×10^(-9) 과 1.8㎒/℃였다. 이 결과로부터 두 펀광성분의 맥놀이 주파수를 이용한 안정화 방법이 출력차의 방법보다 10배 이상의 우수한 주파수 안정화 특성을 갖고 있음을 알 수 있었다. The frequency of the 633 nm internal mirror He-Ne laser has been stabilized by using the beat frequency and the intensity difference between two Zeeman split components in a transverse magnetic field. The frequency stability and the frequency temperature coefficient for the beat frequency method was 7.0×10-¹¹ and 170㎑/℃, respectively, and those for the intensity difference was 1.1×10^(-9) and 1.8㎒/℃, respectively.
정전용량형 변위 센서 신호 처리 회로 개발 및 성능 평가
김종안(Jong-Ahn Kim),김재완(Jae Wan Kim),엄태봉(Tae Bong Eom),강주식(Chu-Shik Kang) Korean Society for Precision Engineering 2007 한국정밀공학회지 Vol.24 No.9
A signal conditioning circuit for capacitive displacement sensors was developed using a high frequency modulation/demodulation method, and its performance was evaluated. Since capacitive displacement sensors can achieve high resolution and linearity, they have been widely used as precision sensors within the range of several hundred micrometers. However, they inherently have a limitation in low frequency range and some nonlinearity characteristics and so a specially designed signal conditioning circuit is needed to handle these properties. The developed signal processing circuit consists of three parts: linearization, modulation/demodulation, and nonlinearity compensation. Each part was constructed discretely using several IC chips and passive elements. An evaluation system for precision displacement sensors was developed using a laser interferometer, a precision stage, and a PID position controller. The signal processing circuit was tested using the evaluation system in the respect of resolution, repeatability, linearity, and so on. From the experimental results, we know that a highly linear voltage output can be obtained successfully, which is proportional to displacement and the nonlinearity of output is less than 0.02% of full range. However, in the future, further investigation is required to reduce noise level and phase delay due to a low-pass filter. The evaluation system also can be applied effectively to calibration and evaluation of precision sensors and stages.
김종안(Jong-Ahn Kim),김재완(Jae Wan Kim),강주식(Chu-Shik Kang),엄태봉(Tae Bong Eom) Korean Society for Precision Engineering 2009 한국정밀공학회지 Vol.26 No.8
We developed a line standards measurement system using an optical microscope and measured two kinds of line standards. It consists of three main parts: an optical microscope module including a CCD camera, a stage system with a linear encoder, and a measurement program for a microscopic image processing. The magnification of microscope part was calibrated using onedimensional gratings and the angular motion of stage was measured to estimate the Abbe error. The threshold level in linewidth measurement was determined by comparing with certified values of a linewidth reference specimen, and its validity was proved through the measurement of another linewidth specimen. The expanded uncertainty (k=2) was about 100 ㎚ in the measurements of 1 ㎛~10 ㎛ linewidth. In the comparison results of line spacing measurement, two kinds of values were coincide within the expanded uncertainty, which were obtained by the one-dimensional measuring machine in KRISS and the line standards measurement system. The expanded uncertainty (k=2) in the line spacing measurement was estimated as √(0.098 ㎛)² + (1.8×10?⁴×L). Therefore, it will be applied effectively to the calibration of line standards, such as linewidth and line spacing, with the expanded uncertainty of several hundreds nanometer.
나노미터 영역 길이 측정을 위한 미터 소급성을 갖는 원자간력 현미경 개발
김종안(Jong-Ahn Kim),김재완(Jae Wan Kim),박병천(Byong Chon Park),엄태봉(Tae Bong Eom),홍재완(Jae Wan Hong) Korean Society for Precision Engineering 2004 한국정밀공학회지 Vol.21 No.11
A metrological atomic force microscope (M-AFM) was developed for the length measurements of nanometer range, through the modification of a commercial AFM. To eliminate nonlinearity and crosstalk of the PZT tube scanner of the commercial AFM, a two-axis flexure hinge scanner employing built-in capacitive sensors is used for X-Y motion instead of PZT tube scanner. Then two-dimensional displacement of the scanner is measured using two-axis heterodyne laser interferometer to ensure the meter-traceability. Through the measurements of several specimens, we could verify the elimination of nonlinearity and crosstalk. The uncertainty of length measurements was estimated according to the Guide to the Expression of Uncertainty in Measurement. Among several sources of uncertainty, the primary one is the drift of laser interferometer output, which occurs mainly from the variation of refractive index of air and the thermal stability. The Abbe error, which is proportional to the measured length, is another primary uncertainty source coming from the parasitic motion of the scanner. The expanded uncertainty (k = 2) of length measurements using the M-AFM is √(4.26)²+(2.84×10-⁴×L)² (㎚), where L is the measured length in ㎚. We also measured the pitch of one-dimensional grating and compared the results with those obtained by optical diffractometry. The relative difference between these results is less than 0.01 %.