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4시 20분부터 제1과학관 31214 e+강의실에서 간단한 다과를 제공합니다.

아 래

Title: Ultrafast Movie Maker for Photo-induced Dynamics: Ultrafast Electron Microscope

Speaker: 장   기   석  박사님 (LG Display)

Date & Time: Mar. 27. (Wed.) 2019 4:30 PM

Place: Natural Science 1,  Room No. 31214

Abstract: Making a ‘molecular movie’ is Holy Grail to directly visualize structural phase transitions among metal, insulator and superconductor and photo-induced non-thermal energy transfer processes. To achieve this, an ‘ultrafast camera’ with simultaneously high spatial and temporal resolution to catch the atomic dynamics is required. The pump-probe technique based on femtosecond pump laser with a electron pulse probe can provide a basic framework for realizing such an ‘ultrafast camera’ although this technology has not achieved its full utility as a universal imaging and spectroscopy tool, due to limitations in generation and preservation of a high–brightness electron beam in the ultrafast regime. To realize the high-brightness electron pulse, the major challenge is overcoming strong Coulomb repulsion among electrons (space-charge effect) in the pulse, because the space–charge effect causes the electron pulse expansion in transverse and longitudinal direction. In this seminar, the high-brightness ultrafast electron beam physics will be introduced with the major components, (1) photoelectron gun, (2) magnetic lenses, and (3) an RF compressor controlling the space-charge effect along transverse and longitudinal direction respectively, and the previous studies about photo-induced surface charge dynamics and structural phase transition in graphene and VO2 will be presented.