• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.363-365
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• 2017

The telescope to be onboard SPICA (Space Infrared Telescope for Cosmology and Astrophysics) has an aperture diameter of 2.5 m and its imaging performance is to be diffraction-limited at a wavelength of $20{\mu}m$ at the operating temperature of <8 K. Because manufacturing precise autocollimating flat mirrors (ACFs) with sizes comparable to the SPICA telescope is not technically feasible, we plan to use sub-aperture stitching interferometry through ACFs for optical testing of the telescope. We have verified the applicability of the sub-aperture stitching technique to the SPICA telescope by performing stitching experiments in a vacuum at a room temperature, using the 800-mm telescope and a 300-mm ACF. We have also developed a new method to reduce uncertainties possibly caused by cryogenic and gravitational deformations of ACFs.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.2
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• pp.107-114
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• 2017

In this investigation, we describe a metrological technique for surface and thickness profiles of a silicon (Si) wafer by using a 6 degree of freedom (DOF) stitching method. Low coherence scanning interferometry employing near infrared light, partially transparent to a Si wafer, is adopted to simultaneously measure the surface and thickness profiles of the wafer. For the large field of view, a stitching method of the sub-aperture measurement is added to the measurement system; also, 6 DOF parameters, including the lateral positioning errors and the rotational error, are considered. In the experiment, surface profiles of a double-sided polished wafer with a 100 mm diameter were measured with the sub-aperture of an 18 mm diameter at $10\times10$ locations and the surface profiles of both sides were stitched with the sub-aperture maps. As a result, the nominal thickness of the wafer was $483.2{\mu}m$ and the calculated PV values of both surfaces were $16.57{\mu}m$ and $17.12{\mu}m$, respectively.

• The Optical Journal
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• s.143
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• pp.46-53
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• 2013

비구면 광학요소는 광학계에 중요한 이점을 제공하는 반면 정밀한 측정에 제한이 많기에 정밀한 비구면의 생산이 어려운 광학 요소이다. 수년 전 부분 구경 스티칭 방법(Subaperture Stitching Interferometry, 이하 SSI$^{(R)}$)의 개발과 이 기술을 기반으로 하는 장비(SSI-A$^{(R)}$)의 도입으로 비구면 형상오차의 정밀한 측정이 가능하게 되었다. 많은 비구면들이 기존의 SSI-A의 영역에 포함되지만 이에 더 나아가 VONTM(Variable Optical Null)을 도입하면 기존의 측정 영역인 비구면도(best fit sphere에서) $100{\sim}200{\lambda}$대에서 약 $1000{\lambda}$까지 확장하여 측정할 수 있다. 본고에서는 지난 2012년 10월 23일 진행된 QED의 기술강연회에서 발표된 내용 중 VONTM의 원리와 이를 이용한 SSI$^{(R)}$ 기술이 도입된 장치인 ASI$^{(R)}$(Aspheric Stitching Interferometer)의 측정결과를 그 동안 각종 학회 등에서 발표된 자료들을 통하여 소개하도록 하겠다.

• Korean Journal of Optics and Photonics
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• v.34 no.3
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• pp.117-123
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• 2023

The size of an optical surface can significantly affect the performance of an optical system, and high spatial frequency errors have a greater impact. Therefore, it is crucial to measure the surface figure error with high frequency. To address this, a new method called rotational prism stitching interferometer (RPSI) is proposed in this study. The RPSI is a type of stitching interferometer that enhances spatial resolution, but it differs from conventional stitching interferometers in that it does not require the movement of either the mirror tested or the interferometer itself to obtain sub-aperture interferograms. Instead, the RPSI uses a beam expander and a rotating Dove prism to select particular sub-apertures from the entire aperture. These sub-apertures are then stitched together to obtain a full-aperture result proportional to the square of the beam expander's magnification. The RPSI's effectiveness was demonstrated by measuring a 40 mm diameter spherical mirror using a three-magnification beam expander and comparing the results with those obtained from a commercial interferometer. The RPSI achieved surface testing results with nine times higher sampling density than the interferometer alone, with a small difference of approximately 1 nm RMS.