Apparatus and methods for generating and enhancing Smith-Purcell radiation

Patent metadata

Field	Value
Publication number	US-10505334-B2
Application number	US-201815944360-A
Country	US
Kind code	B2
Filing date	Apr 3, 2018
Priority date	Apr 3, 2017
Publication date	Dec 10, 2019
Grant date	Dec 10, 2019

Abstract

An apparatus for generating Smith-Purcell radiation having at least one spectral component at a wavelength λ includes a periodic structure including a dielectric material and an electron source, in electromagnetic communication with the periodic structure, to emit an electron beam propagating within about 5λ from a surface of the periodic structure to induce emission of the Smith-Purcell radiation. The electron beam has an electron energy tunable between about 0.5 keV and about 40 keV so as to change a wavelength of the Smith-Purcell radiation.

First claim

The invention claimed is:

1. An apparatus for generating Smith-Purcell radiation having a spectral component at a wavelength λ, the apparatus comprising:
a periodic structure comprising a dielectric material; and
an electron source, in electromagnetic communication with the periodic structure, to emit an electron beam propagating within about 5λ from a surface of the periodic structure to induce emission of the Smith-Purcell radiation, the electron beam having an electron energy tunable between about 0.5 keV and about 40 keV so as to change the wavelength of the Smith-Purcell radiation,
wherein the electron source comprises a gated field emitter array (FEA).

2. The apparatus of claim 1 , wherein the periodic structure comprises a silicon grating having a periodicity along a first direction and the electron source is configured to emit the electron beam in the first direction.

3. The apparatus of claim 1 , wherein the periodic structure defines at least one bound state in the continuum (BIC) at a bound state wavelength λ B and the electron source is configured to emit the electron beam having an electron velocity v between about 0.9×ac/(mλ B ) and 1.1×ac/(mλ B ), where a is a period of the periodic structure, c is the speed of light in vacuum, and m is a positive integer.

4. The apparatus of claim 3 , wherein the periodic structure is characterized by an in-plane symmetry.

5. The apparatus of claim 1 , wherein the periodic structure has a period of about 50 nm to about 300 nm, the electron energy is substantially equal to or less than 2 keV, and the wavelength of the Smith-Purcell radiation is about 300 nm to about 1600 nm.

6. The apparatus of claim 1 , wherein the periodic structure comprises a corrugated optical waveguide.

7. The apparatus of claim 1 , wherein the periodic structure and the gated FEA are fabricated in a semiconductor substrate.

8. The apparatus of claim 1 , further comprising:
a laser, in optical communication with the FEA, to illuminate the FEA with a light pulse so as to generate the electron beam comprising at least one electron bunch having a duration substantially equal to or less than 1 ps.

9. The apparatus of claim 1 , further comprising:
a depressed collector, operably coupled to the FEA, to receive the electron beam and recycle at least a portion of kinetic energy of the electron beam.

10. The apparatus of claim 1 , wherein a grazing angle of the electron beam with respect to the surface of the periodic structure is substantially equal to or less than 5°.

11. The apparatus of claim 1 , wherein the electron source is configured to emit the electron beam with an elliptical beam profile having a major axis perpendicular to a propagation direction of the electron beam.

12. An apparatus for generating Smith-Purcell radiation having a spectral component at a wavelength λ, the apparatus comprising:
a periodic structure comprising a dielectric material; and
an electron source, in electromagnetic communication with the periodic structure, to emit an electron beam propagating within about 5λ from a surface of the periodic structure to induce emission of the Smith-Purcell radiation, the electron beam having an electron energy tunable between about 0.5 keV and about 40 keV so as to change the wavelength of the Smith-Purcell radiation,
wherein the periodic structure comprises a two-dimensional (2D) photonic crystal characterized by a first dispersion line and the electron beam is characterized by a second dispersion line overlapping with at least a portion of the first dispersion line so as to generate the Smith-Purcell radiation with a bandwidth BW=av/c, where a is a period of the periodic structure, v is a speed of the electron beam, and c is the speed of light.

13. The apparatus of claim 12 , wherein the bandwidth of the Smith-Purcell radiation is substantially equal to or greater than 100 nm.

14. An apparatus for generating Smith-Purcell radiation having a spectral component at a wavelength λ, the apparatus comprising:
a periodic structure comprising a dielectric material, and
an electron source, in electromagnetic communication with the periodic structure, to emit an electron beam propagating within about 5λ from a surface of the periodic structure to induce emission of the Smith-Purcell radiation, the electron beam having an electron energy tunable between about 0.5 keV and about 40 keV so as to change the wavelength of the Smith-Purcell radiation,
wherein the periodic structure comprises a two-dimensional (2D) photonic crystal characterized by a photonic band structure having a flat band and the electron beam is characterized by a dispersion line overlapping with at least a portion of the flat band so as to generate supercollimation.

15. A method for generating Smith-Purcell radiation having a spectral component at a wavelength λ, the method comprising:
generating an electron beam using a gated field emitter array (FEA) fabricated in a semiconductor substrate;
propagating the electron beam within about 5λ from a surface of a periodic structure comprising a dielectric material and fabricated in the semiconductor substrate, the electron beam inducing emission of the Smith-Purcell radiation; and
changing an electron energy of the electron beam between about 0.5 keV and about 40 keV to change a wavelength of the Smith-Purcell radiation.

16. The method of claim 15 , wherein emitting the electron beam comprises propagating the electron beam along a first direction and the periodic structure comprises a silicon grating having a periodicity along the first direction.

17. The method of claim 15 , wherein the periodic structure defines at least one bound state in the continuum (BIC) at a bound state wavelength λ B and emitting the electron beam comprises propagating the electron beam with an electron velocity v between about 0.9×ac/(mλ B ) and 1.1×ac/(mλ B ), where a is a period of the periodic structure, c is the speed of light in the vacuum, and m is a positive integer.

18. The method of claim 15 , wherein the periodic structure has a period of about 100 nm to about 300 nm, the electron energy is substantially equal to or less than 2 keV, and the wavelength of the Smith-Purcell radiation is about 400 nm to about 1500 nm.

19. The method of claim 15 , wherein emitting the electron beam comprises propagating the electron beam near the surface of a corrugated optical waveguide.

20. The method of claim 15 , further comprising:
illuminating the FEA with a light pulse so as to generate the electron beam with at least one electron bunch having a duration substantially equal to or less than 1 ps.

21. The method of claim 15 , further comprising:
receiving the electron beam; and
recycling at least a portion of kinetic energy of the electron beam using a depressed collector.

22. The method of claim 15 , wherein emitting the electron beam comprises propagating the electron beam at a grazing angle substantially equal to or less than 5° with respect to the surface of the periodic structure.

23. The method of claim 15 , wherein emitting the electron beam comprises emitting the electron beam with an elliptical beam profile having a major axis perpendicular a propagation direction of the electron beam.

24. A method for generating Smith-Purcell radiation having a spectral component at a wavelength λ, the method comprising:
emitting an electron beam to propagate within about 5λ from a surface of a periodic structure comprising

Assignees

• Massachusetts Inst Technology

Inventors

• Yang Yi
• Massuda Aviram
• Roques-Carmes Charles
• Rivera Nicholas H
• Dubcek Tena
• Joannopoulos John D
• Berggren Karl Kimon
• Kaminer Ido E
• Soljacic Marin
• Yang Yujia
• Kooi Steven E
• Keathley Phillip Donald

Classifications

• H01J7/44

  One or more circuit elements structurally associated with the tube or lamp · CPC title

• H01S3/0903 Primary

  Free-electron laser · CPC title

• H01S3/08009

  using a diffraction grating · CPC title

• H01J23/06

  Electron or ion guns · CPC title

• H01J9/02

  Manufacture of electrodes or electrode systems · CPC title