title: Production of electron vortex beams carrying large orbital angular momentum using spiral zone plates.
abstract: We report the production of electron vortex beams carrying large orbital angular momentum (OAM) using micro-fabricated spiral zone plates. A series of the spherical waves, focussing onto different positions along the propagating direction of the electron beam, were observed. The nth order vortex beam has an OAM n times larger than that of the first-order vortex beam. We observed an electron vortex with an OAM up to   in a high-order diffracted wave. A linear dependence of the diameter of the vortex beam on the OAM was observed, being consistent to numerical simulations.
authors.forename: Koh
authors.initials: K
authors.lastname: Saitoh
authors.forename: Yuya
authors.initials: Y
authors.lastname: Hasegawa
authors.forename: Nobuo
authors.initials: N
authors.lastname: Tanaka
authors.forename: Masaya
authors.initials: M
authors.lastname: Uchida