Electron microscope and a method of imaging objects

1. A method of imaging an object, including the steps of:

generating at least one electron pulse, each electron pulse including a plurality of electrons with the electrons having a kinetic energy spread;

demagnifying each electron pulse using one or more lenses, each lens having a focal strength;

dynamically varying said focal strength of at least one of said one or more lenses to compensate for said kinetic energy spread; and

forming an image of said object based on interactions at said object resulting from each demagnified pulse.

2. A method as claimed in claim 1 further comprising the step of providing a drift tube for slowing each electron pulse to enhance spatial separation of the electrons in each electron pulse.

3. A method as claimed in claim 2 wherein each electron pulse is substantially demagnified on a point on said object.

4. A method as claimed in claim 3 wherein said step of demagnifiying comprises the step of providing a lens to demagnify each electron pulse, and providing a voltage at or within said lens.

5. A method as claimed in claim 4 wherein said step of dynamically varying the focal strength comprises dynamically varying the voltage at said lens, to vary the focal strength at said object.

6. A method as claimed in claim 5 wherein said voltage is varied according to a predetermined waveform.

7. A method as claimed in claim 6 wherein said predetermined waveform is a triangular waveform.

8. A method as claimed in claim 7 wherein the rate of change of said triangular waveform is greater than 0.5V/ns.

9. A method as claimed in claim 8 wherein said predetermined waveform having a period matching the period of pulsed electron beam.

10. A method as claimed in claim 1 wherein the width of said generated pulse is less than 100 ps.

11. An electron microscope for imaging an object, said microscope comprising:

an electron source adapted to produce a plurality of electron pulses, each electron pulse including a plurality of electrons with the electrons having a kinetic energy spread;

one or more lenses adapted to demagnify each of said electron pulses at said object, each lens having a focal strength;

compensation means for dynamically varying said focal strength of at least one of said one or more lenses to compensate for said kinetic energy spread; and

a detector for forming an image of said object based on interactions at said object resulting from each of said demagnified pulses.

12. The electron microscope as claimed in claim 11 wherein said compensation means is adapted such that the focal length of said lens corresponds substantially to a point on said object for each electron pulse.

13. The electron microscope as claimed in claim 11 further comprising an axis between said electron source and said object, and a drift tube juxtaposed about said axis adapted for slowing each electron pulse to enhance spatial separation of the electrons in each electron pulse.

14. The electron microscope as claimed in claim 13 wherein said one or more lenses comprises a condenser lens juxtaposed about said axis after said drift tube.

15. The electron microscope as claimed in claim 13 wherein said one or more lenses further comprises an objective lens juxtaposed about said axis proximate said object.

16. The electron microscope as claimed in claim 15 further comprising a signal generator adapted to supply a dynamically varying voltage to an electrode within said objective lens, wherein said dynamically varying voltage is adapted to substantially compensate the focal strength of said objective lens for said kinetic energy spread.

17. The electron microscope as claimed in claim 16 wherein said signal generator is further adapted to supply a triangular waveform voltage to said electrode.

18. The electron microscope as claimed in claim 17 wherein said signal generator is further adapted to supply said triangular waveform with a rate of change of greater than 0.5V/ns.

19. The electron microscope as claimed in claim 13 further comprising one or more scan coils juxtaposed about said axis adapted to direct each of said demagnified pulses progressively over said object to produce interactions at said object.

20. The electron microscope as claimed in claim 11 wherein said electron source is further adapted to produce pulses widths of less than 100 ps.

21. The electron microscope as claimed in claim 11 wherein said electron source comprises an electron gun of a type selected from the group of tungsten, cold field emission, and laser pulsed photocathode.

22. The electron microscope as claimed in claim 21 wherein said electron gun is pulsed to produce said plurality of electron pulses.

23. The electron microscope as claimed in claim 21 wherein said electron gun produces a continuous beam of electrons and said electron source further comprising a beam banker unit juxtaposed about said axis and adapted to produce said plurality of electron pulses from said continuous beam.