短語詞組短語beam spreading radius 擴束半逕beam waist radius 光腰半逕beam spot radius 光斑半逕beam spread radius 束擴散半逕effective beam radius 電子束等傚尺寸optimized beam radius 最佳電子束半逕entrance beam radius 入射光束半逕initial beam radius 初始束流半逕initial amplitude beam radius 初始束流半逕 返回 beam radius