Method of investigating the wavefront of a charged-particle beam

1. A method of investigating a wavefront of a charged-particle beam that is directed from a source through an illuminator so as to traverse a sample plane and land upon a detector, an output of the detector being used in combination with a mathematical reconstruction technique so as to calculate at least one of phase information and amplitude information for the wavefront at a pre-defined location along its path to the detector in which:

said beam is caused to traverse a particle-optical lens system disposed between said sample plane and said detector;

at a selected location in the path from said source to said detector, a modulator is used to locally produce a given modulation of the wavefront;

in a series of measurement sessions, different such modulations are employed, and the associated detector outputs are collectively used in said mathematical reconstruction;

wherein said selected location is disposed in an image space of said lens system.

2. A method according to claim 1 , wherein said modulation is selected from the group comprising amplitude modulation, phase modulation, and combinations hereof.

3. A method according to claim 1 , wherein said selected location is disposed at or proximal an image plane of said lens system.

4. A method according to claim 3 wherein the modulator comprises a phase modulator.

5. A method according to claim 1 , wherein the modulator comprises:

at least one masking plate;

an actuator system that can be used to adjust a parameter selected from the group comprising:

a position of said masking plate relative to an optical axis of said lens system;

a rotational stance of said masking plate relative to said optical axis;

a shape of said masking plate;

a size of said masking plate,

and combinations hereof.

6. A method according to claim 1 wherein the modulator comprises a phase modulator.

7. A method according to claim 6 , wherein the modulator comprises

at least one phase modulating element;

an adjustment system that can be used to adjust a parameter selected from the group comprising:

a position of said element relative to an optical axis of said lens system;

a rotational stance of said element relative to said optical axis;

an electrical potential or electrical current applied to said element, and combinations hereof.

8. A method according to claim 1 , wherein the illuminator illuminates the sample plane with a substantially planar wavefront.

9. A method according to claim 1 , wherein:

a sample is placed in the sample plane;

wavefront reconstruction is performed for the wavefront as it exits the sample.

10. A method according to claim 1 , wherein said selected location is disposed at or proximal an image plane of said lens system.

11. A method of investigating a wavefront of a charged-particle beam that is directed from a source through an illuminator so as to traverse a sample plane and land upon a detector, an output of the detector being used in combination with a mathematical reconstruction technique so as to calculate at least one of phase information and amplitude information for the wavefront at a pre-defined location along its path to the detector, in which:

said beam is caused to traverse a particle-optical lens system disposed between said sample plane and said detector;

at a selected location in the path from said source to said detector, a modulator is used to locally produce a given modulation of the wavefront;

in a series of measurement sessions, different such modulations are employed, and the associated detector outputs are collectively used in said mathematical reconstruction, wherein

no sample is placed in the sample plane;

wavefront reconstruction is performed for the wavefront as it enters the sample plane.

12. A method according to claim 11 , wherein said modulation is selected from the group comprising amplitude modulation, phase modulation, and combinations hereof.

13. An apparatus for performing wavefront reconstruction of a charged-particle beam, comprising:

a source of charged particles;

an illuminator, for directing charged particles from said source onto a sample plane;

a sample holder located at said sample plane;

a detector, for detecting charged particles traversing the sample plane;

a controller, for analyzing an output from said detector and using it in a mathematical reconstruction technique so as to calculate at least one of phase information and amplitude information for said wavefront at a pre-defined location along its path to the detector, the apparatus further comprising:

a particle-optical lens system disposed between said sample plane and said detector;

a modulator, for producing a given modulation of the wavefront at a selected location in the path from said source to said detector.

14. An apparatus as claimed in claim 13 , wherein:

said particle-optical lens system comprises a series arrangement of an objective lens and a projection lens;

said objective lens is capable of imaging said sample plane onto an image plane;

said modulator is disposed at or proximal said image plane.

15. An apparatus as claimed in claim 13 , which apparatus is comprised in a transmission electron microscope.

16. A method according to claim 3 wherein said modulation is selected from the group comprising amplitude modulation, phase modulation, and combinations hereof.

17. A method according to claim 5 wherein said modulation is selected from the group comprising amplitude modulation, phase modulation, and combinations hereof.

18. A method according to claim 8 wherein said modulation is selected from the group comprising amplitude modulation, phase modulation, and combinations hereof.

19. A method according to any of claims 3 , wherein:

a sample is placed in the sample plane; and

wavefront reconstruction is performed for the wavefront as it exits the sample.