原文由 imrszl(Ins_509a97bd) 发表:
实际上probe correct和image correct进行校正像差的原理都是一样的,probe correct是把不同方向的光汇聚到同一个点,image correct是把同一个点不同方向的光分开。根据reciprocal principle,光路可逆,所以probe correct的光路图反一个方向就是image correct。
球差校正的原理是利用非环形对称的磁场产生的负球差去补偿极靴正的球差系数。episode:早期Scherzer有推导过环形对称极靴的球差计算公式,得到的结论是环形对称的极靴球差系数必然大于0。早期很多人没有注意到这个推论的条件是环形对称,所以觉得球差是不可校正的,因此当时球差校正器被发明时是非常轰动的。
Harold Rose在那篇讲解历史的文章里是这么说Scherzer当年的球差推导公式的:
In 1936, Scherzer proved that chromatic and spherical aberrations of standard electron lenses are unavoidable by transforming each integrand of the corresponding aberration integrals in a sum of positive squared terms. His finding was so important that it was named the “Scherzer theorem.”
但是这个理论是有限制条件的:
The validity of this theorem requires that several conditions are satisfied. Object and image must both be real, the electromagnetic field must be static and rotationally symmetric, the electric potential and its derivatives must be continuous (no space charges within
the region of the electron beam), and the mirror mode has to be excluded.
但在1947年,Scherzer发表文章提出了像差校正的一种思路:
In 1947, Scherzer (1947a) found an ingenious way to enable aberration correction.
He demonstrated in a famous article that it is possible to eliminate chromatic and spherical aberrations by lifting any one of the constraints
of his theorem, either by abandoning rotational symmetry or by introducing time-varying fields, or space charges.
顺便问一句:看那篇文章时看到一句话:In 1964, Deltrap used Archard's suggestion for the construction of a nonsymmetric telescopic quadrupoleoctopole
corrector to eliminate the spherical aberration of a probe-forming lens.
请问这里的telescopic怎么理解?套筒式?组合式?谢谢!