Ponderomotive phase plate for transmission electron microscopes

1. A ponderomotive phase plate system for use in a transmission electron microscope (TEM) for high-resolution phase contrast imaging, comprising:

a laser source for producing a laser beam; and

means for transporting said laser beam into a post-sample electron beam drift space of a post-condenser lens system of said TEM as a focused laser crossover that intersects and partially overlaps the post-sample electron beam at a diffraction plane so that a ponderomotive potential of said focused laser crossover produces a scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a phase contrast transfer function.

2. The ponderomotive phase plate system of claim 1 , further comprising:

means for controlling a spatial profile of said focused laser crossover to control the ponderomotive potential of said focused laser crossover and thereby tailor the scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a desired phase contrast transfer function.

3. The ponderomotive phase plate system of claim 1 , further comprising:

a post-condenser lens body of said post-condenser lens system surrounding the post-sample electron beam drift space and having a port providing access to the post-sample electron beam drift space with said means for transporting operably connected to said port.

4. The ponderomotive phase plate system of claim 1 , further comprising:

means for transporting a second laser beam into the post-sample electron beam drift space as a second focused laser crossover that intersects and partially overlaps the post-sample electron beam at the diffraction plane substantially transverse to the first laser beam so that the ponderomotive potentials of said first and second focused laser crossovers produce a scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a phase contrast transfer function.

5. The ponderomotive phase plate system of claim 1 , further comprising:

a beam dump for capturing the laser beam after intersecting with the post-sample electron beam.

6. The ponderomotive phase plate system of claim 1 ,

wherein the diffraction plane is a back focal plane of an objective lens system of said post-condenser lens system of said TEM.

7. The ponderomotive phase plate system of claim 1 ,

wherein said laser source is a pulsed laser source for producing a pulsed laser beam.

8. An improved transmission electron microscope (TEM) for high-resolution phase contrast imaging, said TEM of a type having an electron source for producing an electron beam, an accelerator for accelerating the electron beam, a condenser lens system for primary beam formation of the electron beam, a sample stage for holding a sample, a post-condenser lens system for focusing the electron beam onto the sample and projecting the post-sample electron beam, and a camera for imaging the sample from the projected post-sample electron beam, the improvement comprising:

a laser source for producing a laser beam; and

means for transporting said laser beam into a post-sample electron beam drift space of the post-condenser lens system via a port in a post-condenser lens body thereof as a focused laser crossover that intersects and partially overlaps the post-sample electron beam at a diffraction plane so that a ponderomotive potential of said focused laser crossover produces a scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a phase contrast transfer function.

9. The improved TEM of claim 8 , wherein the improvement further comprises:

means for controlling a spatial profile of said focused laser crossover to control the ponderomotive potential of said focused laser crossover and thereby tailor the scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a desired phase contrast transfer function.

10. The improved TEM of claim 8 , wherein the improvement further comprises:

means for transporting a second laser beam into the post-sample electron beam drift space as a second focused laser crossover that intersects and partially overlaps the post-sample electron beam at the diffraction plane substantially transverse to the first laser beam so that the ponderomotive potentials of said first and second focused laser crossovers produce a scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a phase contrast transfer function.

11. The improved TEM of claim 8 , wherein the improvement further comprises:

a beam dump for capturing the laser beam after intersecting with the post-sample electron beam.

12. The improved TEM of claim 8 ,

wherein the diffraction plane is a back focal plane of an objective lens system of said post-condenser lens system of said TEM.

13. The improved TEM of claim 8 ,

wherein said laser source is a pulsed laser source for producing a pulsed laser beam.

14. A method of controlling a phase-contrast transfer function of a transmission electron microscope (TEM) for high-resolution phase contrast imaging, comprising:

transporting said laser beam into a post-sample electron beam drift space of a post-condenser lens system of said TEM as a focused laser crossover that intersects and partially overlaps the post-sample electron beam at a diffraction plane so that a ponderomotive potential of said focused laser crossover produces a scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a phase contrast transfer function.

15. The method of claim 14 , further comprising:

controlling a spatial profile of said focused laser crossover to control the ponderomotive potential of said focused laser crossover and thereby tailor the scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a desired phase contrast transfer function.

16. The method of claim 14 , further comprising:

wherein said laser beam is transported into the post-sample electron beam drift space of the post-condenser lens system of said TEM via a port in a post-condenser lens body of said post-condenser lens system surrounding the post-sample electron beam drift space.

17. The method of claim 14 , further comprising:

transporting a second laser beam into the post-sample electron beam drift space as a second focused laser crossover that intersects and partially overlaps the post-sample electron beam at the diffraction plane substantially transverse to the first laser beam so that the ponderomotive potentials of said first and second focused laser crossovers produce a scattering-angle-dependent phase shift in the electrons of said post-sample electron beam corresponding to a phase contrast transfer function.

18. The method of claim 14 , further comprising:

using a beam dump to capture the laser beam after intersecting with the post-sample electron beam.

19. The method of claim 14 ,

wherein the diffraction plane is a back focal plane of an objective lens system of said post-condenser lens system of said TEM.

20. The method of claim 14 ,

wherein the transported laser beam is a pulsed laser beam.