报告题目：Advanced Optical Metrology and Fabrication using Mode-locked Lasers
报 告 人：Seung-Woo Kim
Precision is a common aspect that governs most of today’s leading-edge technologies including IT, BT, NT and aerospace technology. In response to ever-growing demands on precision, various laser sources have been used to attain sub-wavelength precision in many fields of fabrication and metrology by means of photons. This precision-directed laser-based photonics will continue to advance to the direction of ultraprecision to achieve better resolutions, larger functional ranges, higher throughputs, and more improved stability. Nonetheless, the light sources available today are limited in the wavelength bandwidth, photon energy, spatial and temporal coherence, and peak power, which consequently hinders breakthroughs toward the realm of ultraprecision. The research objective of the Precision Engineering & Metrology Group at KAIST is to investigate the technological possibilities of ultrashort mode-locked lasers with the aim of establishing the new foundations for ultraprecision that will enable nano-fabrication and distance and dimensional metrology over extensive ranges as demanded in the next generation of precision engineering. To the end, a systematic approach will be pursued to generate noble coherent light sources covering the broad optical spectrum spanning from THz waves, infrared, visible to extreme violet light radiation by making the most of ultrafast femtosecond laser pulse.
报告题目：3D Coordinate Measurement System Based on Absolute Distance Interferometer
报 告 人：Jeong-Seok Oh
In recent years, a mobile manufacturing system capable of overcoming space limitations and realizing a large-scale precision machining has been actively researched for precise manufacturing and repairing large complex structures in aviation, shipbuilding, energy and plant industries. In order to implement the mobile manufacturing system, techniques for acquiring information about positions and paths of the mobile system in a three-dimensional (3D) space are required. Furthermore, for applying the system to the industrial field, it is necessary to develop a 3D coordinate measurement method which can overcome interference problems caused by obstacles and ensure measurement accuracy in a wide area. With all these requirements we are developing a 3D coordinate measurement system based on tracking multiple absolute distances. There are three key technologies: (1) absolute distance measurement that enables real-time continuous measurement with high accuracy after the obstruction. (2) laser tracking system to track the target, (3) multilateration system that incorporates former ones. This presentation introduces these key technologies in the 3D coordinate measurement system and discusses about preliminary results.
报告题目：Improvement on 3D Optical Measurement Technology for Industrial Applications
报 告 人：Ki-Nam Joo
Ki-Nam Joo，博士，朝鲜大学（Chosun University）光子工程系教授，主要研究方向为尺寸测量、光学表面测量、光学位移以及距离测量、计量学上的飞秒激光应用等，共发表高水平期刊论文20多篇，国际专利10余项，并在国际会议上发表演讲50多次。
Optical dimensional metrology is always important for designing, manufacturing and repairing precise high functional products such as semiconductors, display panels and minute mechanical components. For last two decades, many kinds of measurement technologies had been proposed and developed so they have been realized as commercial measurement or inspection tools in industrial fields. However, it seems that fundamental measurement technologies are recently matured and the trend of technology development focuses on specific applications, which needs several important performances such as high measurement speed, high precision and cost reduction. It is important to know and find the proper technologies to cope with difficulties occurred in measurement and inspection of the products as demands.
In this presentation, research works for three categories of application fields in Chosun University (CU) will be given and show our approaches and concerns. These fields are surface measurements, film structure characterizations and distance measurements. For surface metrology, low coherence interferometer and structure illumination microscopy are presented. LASIE, SPARSE and MYFIELM named by CU are explained for characterizing multi-film structures. The proximity optical sensor developed in CU is given as a distance measurement tool. Based on well-known basic technologies, the advanced and interesting techniques were implemented and the performances of typical metrological tools were improved. I hope this presentation can support the audience having new inspiration and collaborating with each other.
报告题目：Advanced Ultra-precision Machining Technology using High-power Femtosecond Laser
报 告 人：Byunggi Kim
Femtosecond laser is one of the most useful tools for advanced micromachining of various materials such as metals, semiconductors, thin films, and even dielectrics. Conventional laser micromachining technology is based on thermal ablation of materials irradiated by laser spot. Therefore, resolution and precision of the processing is limited by beam diffraction limit and thermal diffusion length, and thermally induced damage is inevitable. On the other hand, as pulse width of femtosecond laser is shorter than electron-lattice coupling time, relatively more precise machining can be performed by using femtosecond laser. Also, thanks to its extremely high peak intensity, femtosecond laser can be used to induce non-thermal ablation based on ultrafast nonlinear optical phenomena.
In this presentation, recent research works of ultra precision manufacturing group of PEM laboratory will be represented. We have developed advanced micromachining technologies based on understandings of nonlinear optical phenomena induced by high-power femtosecond laser. The research topics are categorized as non-thermal machining of dielectric materials, thin film patterning with sub-wavelength resolution, and ultra-precision machining of composite materials. Behavior of free electrons which are produced by high-intensity ultrafast laser pulse has been investigated by using pump-probe spectroscopy and taken into advantage for cutting and drilling of dielectric substrate materials. Also, thin film patterning with sub-wavelength precision has been realized by using femtosecond laser-induced forward transfer (f-LIFT) technique. By using tightly focused fiber femtosecond laser beam with high repetition rate, continuous Au line with nanoscale linewidth was printed on a separated substrate. In addition, examples of advanced micromachining by using femtosecond laser such as carbon fiber reinforced plastic (CFRP) drilling, Si scribing, PI film cutting etc. will be introduced. In conclusion, we hope to have informative discussions on our on-going research topics and trend for development of advanced manufacturing technology.
报告题目：Instant 3D Optical Imaging by Ultrafast Pulses
报 告 人：Daehee Kim
Optical imaging has become a promising technique used as diagnosis and inspection tools in various fields. Most of the traditional imaging techniques aim at improving the spatial resolution below the diffraction limit in order to observe tiny features. Recently, instantaneous imaging is introduced to capture the specific moment of timely varying phenomena. Especially, an instant 3D optical imaging method is necessary for clarifying rapid physical, chemical and dynamic phenomena obviously in time domain.
In this presentation, we propose a single pulse interferometry (SPI) which can instantly collect 3D images based on ultrashort optical pulses. SPI is capable of freezing and capturing 3D images at a specific moment for repeatable and non-repeatable timely varying situations with ultrashort pulse duration even though an imaging device has much longer exposure time. By synchronizing the repetition rate of the pulse train and the frame rate of camera, only a single pulse is used as the illumination light and an interferometric configuration can acquire the phase information of a target. In order to verify the performances of SPI, feasible experiments were performed with ultrashort pulse lasers in comparison with continuous wave (cw) optical sources.