There are no evident energy gain when the focal spot size is too big or small.

电子的能量增益有一个最佳焦斑大小.

Under the different laser parameters, the electron energy gain depends on the laser intensity, focal spot size and pulse width.

不同激光参鼍条件下，得到了电子的能量增益与激光强度、焦斑大小和脉冲宽度关系。