Study on the optical properties of the magnetic circuit corner shape of the magnetic lens.

In this paper, we aim to improve the optical properties of magnetic lenses in transmission electron microscope(TEM). First, the mathematical model of the magnetic field is established, and the formula of the reluctance of the magnetic lens at the corner of the magnetic circuit is deduced. The calculation results of the reluctance are obtained by the numerical analysis method. Then, we find that the corner reluctance affects the density distribution of the magnetic flux lines at the corner. Therefore, the structural shape of the corner of the magnetic lens is optimized. The magnetic flux density on optical axis and the corresponding electron optical parameters are obtained by calculations and simulations. The optical properties of the magnetic lens are improved after the optimization.