二段偏向系

double-deflection system

[目次：レンズ系]

二組の偏向コイルが上下対になっている系。第2コンデンサーレンズと対物レンズの間に置かれ、一段目のコイルで電子ビームを偏向し、二段目のコイルで偏向したビームを振り戻す。電圧軸合わせ、対物レンズの球面収差によるボケのない暗視野像を得るとき、STEM像を得るとき、ホローコーン照射をするときなどに使われる。

The "double-deflection system" is designed in such a way that two pairs of deflection coils are arranged in the vertical direction. The "double-deflection system" is composed of two pairs of deflection coils. It is placed between the objective lens and the second condenser lens. The electron beam is deflected by the first-stage coils and then, the deflected electron beam is deflected again by the second-stage coils. The system is used for various purposes, such as adjustment of the accelerating voltage center, acquisition of a dark-field image without blurring due to spherical aberration of the objective lens, taking a STEM image, and hollow-cone beam illumination.

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