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Phase-sensitive imaging of diffracted light by single nanoslits: measurements from near to far field
Kihm, Hyun-woo,Kihm, Q. H.,Kim, D. S.,Ahn, K. J.,Kang, J. H. The Optical Society 2010 Optics express Vol.18 No.15
<P>We perform phase-sensitive imaging of optical wavefront emanating from a single nanoslit and propagating into free space by using scattering type near-field scanning optical microscope combined with an optical interferometer. By analyzing polarization resolved optical amplitudes and phases, the propagation directions of surface waves are determined and the phase difference between two orthogonal polarization components of the surface wave are discussed for increasing distance from the slit.</P>
Bipod flexure for 1-m primary mirror system.
Kihm, Hagyong,Yang, Ho-Soon,Lee, Yun-Woo American Institute of Physics 2014 Review of scientific instruments Vol.85 No.12
<P>We present an analytical formulation of the bipod flexure for mounting the 1-m primary mirror in a space telescope. Compliance and stiffness matrices of the bipod flexure are derived to estimate theoretical performance and to make initial design guidelines. We use finite element analysis to optimize the bipod design satisfying the application requirements. Experimental verification is achieved by vibration test with a dummy mirror system.</P>
Adjustable bipod flexures for mounting mirrors in a space telescope
Kihm, Hagyong,Yang, Ho-Soon,Moon, Il Kweon,Yeon, Jeong-Heum,Lee, Seung-Hoon,Lee, Yun-Woo The Optical Society 2012 Applied Optics Vol.51 No.32
<P>A new mirror mounting technique applicable to the primary mirror in a space telescope is presented. This mounting technique replaces conventional bipod flexures with flexures having mechanical shims so that adjustments can be made to counter the effects of gravitational distortion of the mirror surface while being tested in the horizontal position. Astigmatic aberration due to the gravitational changes is effectively reduced by adjusting the shim thickness, and the relation between the astigmatism and the shim thickness is investigated. We tested the mirror interferometrically at the center of curvature using a null lens. Then we repeated the test after rotating the mirror about its optical axis by 180 in the horizontal setup, and searched for the minimum system error. With the proposed flexure mount, the gravitational stress at the adhesive coupling between the mirror and the mount is reduced by half that of a conventional bipod flexure for better mechanical safety under launch loads. Analytical results using finite element methods are compared with experimental results from the optical interferometer. Vibration tests verified the mechanical safety and optical stability, and qualified their use in space applications.</P>
Development of the primary mirror for CAS500-1 (Compact Advanced Satellite 500-1)
Kihm Hagyong,Lee Yun-Woo,Yang Ho-Soon,Kim Seonghui,Lee Deog-Gyu 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.6
CAS500-1 (Compact Advanced Satellite 500-1) launched in Mar. 2021 is the first Korean ground observation satellite localizing the entire mirror development, especially the primary mirror M1. M1 is a lightweight concave mirror with a diameter of 0.6 m, and it has 3 square bosses at the rim for flexure mounting. We present the whole development procedure of the flight model M1, including the optomechanical design, fabrication, environmental tests, and a coordinate mapping method for alignment and integration.
Fiber-diffraction interferometer for vibration desensitization.
Kihm, Hagyong,Kim, Seung-Woo Optical Society of America 2005 Optics letters Vol.30 No.16
<P>We describe a new interferometer designed to obtain high immunity to vibration by generating the reference wave by means of fiber diffraction so as to share a common path with the measurement wave. A spatial phase shifter is added to secure vibration desensitization by capturing four phase-shifted interferograms simultaneously without time delay. Experimental results prove that the proposed interferometer is capable of providing stable measurements with a level of fringe stabilization of less than 1 nm in a typical workshop environment equipped with no excessive ground isolation for antivibration.</P>
Utilizing virtual vibration tests to optimize physical endurance tests
Kihm, Frederic Techno-Press 2018 Advances in aircraft and spacecraft science Vol.5 No.2
Physical tests are performed at various stages of the development cycle of a product, from prototype validation to product qualification. Although costly, there are growing demands for qualification tests like endurance vibration testing to be more representative of the real world. At the same time there are growing demands to assess the durability of these items based on FEA simulation. In this paper, we will explain how to set up a CAE-based test and how to correlate the results with some physical measurements. Specific assumptions will be explained and some advantages of using virtual tests will be highlighted such as the reduction of the number of prototypes needed, investigations on failures, evaluation of the level of reliability via sensitivity analysis, evaluation of the margins are at the end of a successful test. This presentation will therefore focus on explaining and showing how virtual tests can enrich the exploitation of physical tests.