1. N. I. Shtepa, Zh. Tekh. Fiz. 49, 1839 (1979) [Sov. Phys. Tech. Phys. 24, 1034 (1979)].
2. N. I. Shtepa, Zh. Tekh. Fiz. 36, 470 (1966) [Sov. Phys. Tech. Phys. 11, 347 (1966–1967)].
3. N. I. Shtepa, Zh. Tekh. Fiz. 48, 2139 (1978).
4. A. A. Rusterholz, Elektronenoptik (Birkhäuser, Basel, 1950; Inostrannaya Literatura, Moscow, 1952).