超快電子顯微鏡中射束動力學之探討

Bunched Beam Dynamics in Femtosecond Electron Microscope

曾斌誠(Ping chen Tseng)

指導教授 ： 施宙聰

國立清華大學/電機資訊學院/光電工程研究所/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00193

摘要

超快電子顯微術運用於觀察材料及生物試片之動態反應，其具有高度空間及時間解析能力。超快電子顯微鏡結合超快雷射及穿透式電子顯微鏡，產生飛秒電子束團來觀察樣品。但是空間電荷效應會劇烈影響飛秒電子束團在行進過程時的行為，像是電子束團變形及能量分散效應。為了暸解空間電荷對電子束團的影響，在本論文中，我們推導coupled envelope equations 來計算空間電荷效應對電子束團橫向及縱向長度變化的影響，並利用模擬軟體 PARMELA 來與其結果比較。我們藉由PARMELA模擬軟體來分析具高斯分佈電子束團在電子顯微鏡內各個元件內的行為且使用POISSON 模擬軟體來計算從穿透式電子顯微鏡拆除下的馬靴極磁透鏡的磁場分布。同時也設計磁透鏡參數來補償空間電荷造成的橫向長度變化。最後我們想出利用RF來補償因空間電荷效應所造成的縱向長度變化，於是使用PARMELA設計RF buncher 參數來分析電子束團在縱向長度上的補償效應。

關鍵字

超快電子顯微鏡 ； 飛秒電子束

並列摘要

Ultrafast electron microscopy harbors femtosecond time resolution and atomic level spatial resolution. In NTHU/NSRRC time-resolved electron microscopy proposal, a transmission electron microscope (TEM) integrated with a femtosecond laser system was used to generate ultrafast electron probe for the study of transient state of various materials and bio samples. Space charge effect influenced such a short bunch seriously and consequently caused bunch broadening and energy spread. In the thesis, we derived coupled envelope equations incorporated with space charge effect as well as external fields and compared with PARMELA simulation code. PARMELA is also used to analyze space charge effect in Gaussian distributed bunch due to laser intensity distribution. The simulation results indicated the tendency of broadening caused by space charge effect is linear in drift space. And halo effect was found in the polepiece lens. In addition, we discussed energy spread of the bunch which related to matter wave dispersion in TEM components. At the end, we designed a RF buncher attached with a solenoid lens to compensate longitudinal and transverse broadening.

並列關鍵字

Ultrafast ； TEM ； Bunched Beam ； coupled envelope equations

參考文獻

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