Anamorphotic quadrupole lens system for highly demagnified round spot

Abstract

Paraxial and aberration properties have been studied theoretically for an electrostatic quadrupole lens system that demagnifies the line shaped emission area with a high aspect ratio of a LaB 6 source to a sub-micron round spot. For a quadrupole lens doublet, it was indicated that the target paraxial performances, M x = 1 100 and M y = 1 1000 , can be achieved with a large object distance by providing a round lens in front of the doublet. However, it was clear that a combined doublet with a round lens is not suitable for practical sub-micron spot optics because the spot growth due to the object distance error by the round lens is not negligible. On the other hand, for a quadrupole lens triplet with a low second lens excitation, the target performances can be obtained by operating the first lens with higher excitation; the aberration properties can be reduced by optimizing the geometrical parameters. Finally, it was recognized that the triplet is suitable for practical anamorphotic optics, in which a 10 μm × 100 μm line source is demagnified to a round spot of 0.1 μm in diameter.