Methods and devices for measuring orbital angular momentum states of electrons

1. A device for enabling measurement of electron orbital angular momentum states in an electron microscope, the device comprising the following components aligned sequentially in the following order along an electron beam axis:

a phase unwrapper (U) that is a first electrostatic refractive optical element comprising an electrode and a conductive plate, where the electrode is aligned perpendicular to the conductive plate;

a first electron lens system (L 1 );

a phase corrector (C) that is a second electrostatic refractive optical element comprising an array of electrodes with alternating electrostatic bias; and

a second electron lens system (L 2 ).

2. The device of claim 1 wherein the phase unwrapper is a needle electrode.

3. The device of claim 2 wherein the needle electrode is a nano-patterned conductive wire supported on an electron-transparent membrane.

4. The device of claim 2 wherein the needle electrode is a cantilevered needle extending into the space of an aperture.

5. The device of claim 1 wherein the phase unwrapper is a knife edge electrode with the edge aligned parallel to the beam axis.

6. The device of claim 1 wherein the phase corrector comprises an array of alternating electrodes.

7. The device of claim 6 wherein the phase corrector comprises an array of nanoscale strip lines running parallel to the beam axis.

8. The device of claim 6 wherein the phase corrector comprises a set of electrodes that book-end the beam.

9. The device of claim 6 wherein the phase corrector comprises two adjacent arrays of electrodes with a ground plate below each.

10. The device of claim 6 wherein the phase corrector comprises a plasmonic device where the necessary field is produced by laser interaction with a flat metal surface.