II. On some, focal properties of an electron optical immersion objective

Abstract

1.The electrolytic tank field plots indicate that a simple exponential law V=Ae ^kz expresses the early portion of the axial potential distribution of the objective. 2.The first focal length has a value of the order of the modulator hole diameter ; it decreases as the cathode/modulator spacing is increased. 3.The variation of focal length with initial velocity is surprisingly small—about 1/2 per cent. from range zero to the most probable velocity (0·0s7 v.). 4.The size of the “crossover” is proportional to both the initial radial velocity and to the angle of ejection (within the paraxial limits). It decreases as the cathode is moved away from the modulator. 5.For constant black-out voltage, the potential of the most probable crossover is independent of geometry. The cathode image moves further and further from the cathode as the spacing is decreased and magnifications of three and over were recorded.