Optical-cavity based ponderomotive phase plate for transmission electron microscopy
An optical cavity is defined by a first mirror and a second mirror. The first mirror has a front surface that includes a first concave mirror. The second mirror has a front surface that includes a second concave mirror. The optical cavity has a resonant optical mode with a small focal spot size. The optical cavity may be used in a method of enhancing phase contrast in an electron beam image, and associated system for electron beam imaging or electron-beam spectroscopy, with a transmission electron beam microscope.
1. A system for electron beam imaging or electron beam spectroscopy comprising:
a transmission electron microscope (TEM) having a back focal plane;
a plurality of mirrors forming an optical cavity, a focal spot of the optical cavity positioned at the back focal plane of the TEM, the optical cavity positioned to allow an electron beam provided by the TEM to pass through the focal spot of the optical cavity, and the optical cavity being operable to admit a laser beam;
a laser coupled to the optical cavity and operable to provide a laser beam of a specified wavelength to enter the optical cavity, the laser beam being reflected from the plurality of mirrors to provide a standing wave optical phase plate focused at the back focal plane of the TEM to cause a modulation of the electron beam; and
an image plane of the TEM positioned to receive the electron beam modulated by the standing wave optical phase plate.
2. The system of claim 1 , wherein the plurality of mirrors comprises a first mirror and a second mirror.
3. The system of claim 1 , wherein a reflective surface of each of the plurality of mirrors is coated with a reflective dielectric coating.
4. The system of claim 1 , wherein a reflectivity of each of the plurality of mirrors is about 0.9 or greater.
5. The system of claim 1 , wherein at least one of the plurality of mirrors has a radius of curvature of 5 cm or less.
6. The system of claim 1 , further comprising:
a cavity housing, having the optical cavity therein and having an adjustable suspension operable for adjustment of angle and position of at least one of the plurality of mirrors.
7. The system of claim 1 , further comprising:
an adjustable suspension including piezoelectric actuators to adjust angle or position of at least one of the plurality of mirrors.
8. A method of enhancing phase contrast in an electron beam image comprising:
generating an electron beam in a transmission electron microscope (TEM) having a back focal plane;
admitting the electron beam along an axis through a center of an optical cavity, the optical cavity being positioned at the back focal plane, and the optical cavity being defined by a first mirror and a second mirror;
admitting a laser beam to the optical cavity, the laser beam being reflected from the first mirror and the second mirror to generate a standing wave optical phase plate focused at the back focal plane of the TEM to cause a modulation of the electron beam; and
imaging the electron beam in an image plane of the TEM positioned to receive the electron beam modulated by the standing wave optical phase plate.
9. The method of claim 8 , wherein the laser beam being reflected from the first mirror and the second mirror comprises the laser beam being reflected by the first mirror with the first mirror having a reflective dielectric coating and the laser beam being reflected by the second mirror with the second mirror having a further reflective dielectric coating.
10. The method of claim 8 , wherein the laser beam being reflected from the first mirror and the second mirror comprises the laser beam being reflected by the first mirror with the first mirror having about 0.9 or greater reflectivity and the laser beam being reflected by the second mirror with the second mirror having about 0.9 or greater reflectivity.
11. The method of claim 8 , wherein the laser beam being reflected comprises the laser beam being reflected by at least one of the first mirror and the second mirror having a radius of curvature of 5 cm or less.
12. The method of claim 8 , further comprising:
adjusting angle or position of the first mirror or the second mirror, in an adjustable suspension.
13. The method of claim 8 , further comprising:
adjusting, with a piezoelectric actuator, angle or position of the first mirror or the second mirror.
14. A device comprising:
a first mirror having a first front surface comprising a first concave mirror;
a second mirror having a second front surface comprising a second concave mirror;
the first mirror or the second mirror having a curvature radius of about 5 cm or less; and
the first mirror and the second mirror defining an optical cavity having a resonant optical mode with focal spot size of about 30 μm or less.
15. The device of claim 14 , wherein the device is operable to: be positioned at a back focal plane of a transmission electron microscope (TEM); admit an electron beam of the TEM; admit a laser beam to the optical cavity, an interaction of the laser beam and the electron beam generating a phase-shift in the electron beam; and allow the electron beam to exit the optical cavity.
16. The device of claim 14 , wherein a reflectivity of each of the first front surface and the second front surface is about 0.9 or greater.
17. The device of claim 14 , wherein a reflectivity of each of the first front surface and the second front surface is about 0.99 or greater.
18. The device of claim 14 , wherein power of a laser beam is amplified by the optical cavity by a factor of about 10 or more.
19. The device of claim 14 , further comprising:
a piezoelectric actuator to adjust position or angle of the first mirror or the second mirror.
20. The device of claim 14 , further comprising:
an adjustable suspension for adjustment and active damping of vibration of the first mirror or the second mirror.