IMAGING SYSTEM

• US 20080237771A1
• Filed: 03/30/2007
• Published: 10/02/2008
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: Subrahmanyam Pilla
• Original Assignee: Subrahmanyam Pilla
• Inventors: Kadiyala, Srinivas, Pilla, Subrahmanyam
• Granted Patent: US 7,728,274 B2
• Time in Patent Office: Days
• US Class Current: 257/458
• CPC Class Codes: H04N 23/11 for generating image signals from visible and infrared light wavelengths
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A viewing system configured to combine multiple spectral images of a scene, the system includes a spectral beam separator configured to split an incoming beam of radiation into a first and a second beam of radiation, the first beam of radiation including radiations substantially in a first spectral band and the second beam of radiation including radiations substantially in a second spectral band; an image intensifier configured to intensify the second beam of radiation, the image intensifier including a photocathode configured to produce a flux of photoelectrons with substantially increased efficiency when exposed to the second beam of radiation, the photocathode constructed and arranged to substantially absorb all the radiations in the second beam of radiation; a current amplifier configured to amplify the flux of photoelectrons; and a display system configured to display an image of the scene in the second spectral band based on the amplified flux of electrons simultaneously with an image of the scene in the first spectral band.

Claims

1. An imaging system comprising:

a spectral beam separator configured to split an incoming beam of radiation into a first and a second beam of radiation, the first beam of radiation including radiations substantially in a first spectral band and the second beam of radiation including radiations substantially in a second spectral band;

an image intensifier configured to intensify the second beam of radiation, the image intensifier including a photocathode configured to produce a flux of photoelectrons when exposed to the second beam of radiation, the photocathode constructed and arranged to substantially absorb all the radiations in the second beam of radiation;

a current amplifier configured to amplify the flux of photoelectrons; and

a display system configured to display an image of a scene in the second spectral band based on the amplified flux of electrons.

2. The system of claim 1, wherein the photocathode includes a plurality of dielectric layers and semiconductor layers that are configured to increase absorption of the radiations of the second beam of radiation in the semiconductor layers.

3. The system of claim 2, wherein the plurality of dielectric layers and semiconductor layers collectively form an optically coherent layer for the second beam of radiation, the coherent layer adapted to produce standing waves within the semiconductor layers.

4. The system of claim 1, wherein the photocathode includes an assembly of semiconductor layers comprising a n+ doped semiconductor layer, an intrinsic semiconductor layer and a p+ doped semiconductor layer having a surface with substantially negative electron affinity.

5. The system of claim 4, wherein the intrinsic semiconductor layer is substantially thicker than the n+ doped semiconductor layer and the p+ doped semiconductor layer.

6. The system of claim 1, wherein substantially all the photoelectrons are generated in an intrinsic semiconductor layer of the photocathode.

7. The system of claim 1, wherein the photocathode includes a metal grid.

8. The system of claim 7, wherein the photocathode includes an insulating layer configured to reduce a flow of dark current into the metal grid.

9. The system of claim 1, wherein the spectral beam separator includes one or more dichroic mirrors.

10. The system of claim 9, wherein the dichroic mirrors are configured such that at least about 90% of the radiations of the second beam of radiation includes radiations in the second spectral band.

11. The system of claim 1, further comprising one or more dielectric coatings configured to reduce an amount of radiations in the first spectral band in the second beam of radiation.

12. The system of claim 1, wherein the current amplifier includes micro channel plates.

13. The system of claim 1, further comprising a phosphor screen configured to emit radiations when exposed to the amplified flux of photoelectrons.

14. The system of claim 1, wherein the second spectral band includes the near infra-red band and, optionally, portions of the deep infra-red band.

15. The system of claim 1, wherein the first spectral band includes the visible band.

16. The system of claim 1, wherein the spectral beam separator and the image intensifier are configured to substantially increase both the external and internal quantum efficiencies.

17. The system of claim 1, further comprising another imaging system configured to display the image of the scene in the first spectral band.

18. The system of claim 17, wherein the image of the scene in the first and second spectral bands are simultaneously displayed.

19. A method for displaying an image of a scene, the method comprising:

splitting an incoming beam of radiation into a first and a second beam of radiation, the first beam of radiation including radiations substantially in a first spectral band and the second beam of radiation including radiations substantially in a second spectral band;

intensifying the second beam of radiation, the intensifying including substantially absorbing in a photocathode all the radiations in the second beam of radiation and producing a flux of photoelectrons when the photocathode is exposed to the second beam of radiation;

amplifying the flux of photoelectrons; and

displaying an image of the scene in the second spectral band based on the amplified flux of electrons.

20. An imaging system comprising:

an image intensifier configured to intensify a beam of radiation, the image intensifier including a negative electron affinity photocathode configured to produce a flux of photoelectrons when exposed to the beam of radiation, the beam of radiation including essentially radiations in a selected spectral band, the photocathode including an intrinsic semiconductor layer and a p+ doped semiconductor layer, the intrinsic semiconductor layer substantially thicker than the p+ doped layer such that substantially all of the photoelectrons are produced in the intrinsic layer;

a current amplifier configured to amplify the flux of photoelectrons; and

a display system configured to display an image of the scene in the selected spectral band associated to the beam of radiation based on the amplified flux of electrons.

21. The system of claim 20, wherein the photocathode further includes a n+ doped semiconductor layer and one or more dielectric layers, the one or more dielectric layers, the n+ doped semiconductor layer, the intrinsic semiconductor layer and the p+ doped semiconductor layer being constructed and arranged to form an optically coherent layer for the beam of radiation, the coherent layer adapted to produce standing waves within the intrinsic semiconductor layer.

22. The system of claim 21, wherein the one or more dielectric layers are selected to reduce transmission of radiations in spectral bands outside the selected spectral band in the beam of radiation.

23. The system of claim 20, further comprising a first and a second electrode to apply a voltage bias within the photocathode to migrate the photoelectrons from the intrinsic semiconductor layer toward the p+ doped semiconductor layer and a substantially thin insulating layer in between intrinsic and p+ doped semiconductor layers to reduce dark current generated in the intrinsic layer.

24. The system of claim 23, wherein the first electrode is a metal electrode positioned proximate a first side of the p+ doped semiconductor layer, the intrinsic layer positioned on a second side of the p+ doped semiconductor layer.

25. The system of claim 24, wherein the first electrode is a metal grid and the insulating layer is a grid substantially matching the first electrode grid.

26. The system of claim 25, wherein the metal grid has a metal surface area that is less than about 20% of a total surface area of the first side of the p+ doped semiconductor layer.

27. The system of claim 25, wherein the metal grid is traversed by the flux of photoelectrons.

28. The system of claim 23, wherein the second electrode is substantially transparent and is in electrical contact with a n+ doped semiconductor layer positioned on the intrinsic semiconductor layer.

29. The system of claim 22, wherein the first side of the p+ layer is cessiated to lower its electron affinity to substantially negative values.

30. The system of claim 29, wherein the insulating layer is positioned between the p+ doped layer and a first electrode, the first electrode part of an electrode assembly that is adapted to apply a voltage bias within the photocathode to migrate the photoelectrons from the intrinsic semiconductor layer toward the p+ doped semiconductor layer.

31. The system of claim 29, wherein the first electrode is a metal grid.

32. The system of claim 30, wherein the metal grid is traversed by the flux of photoelectrons.

33. An image intensifier configured to intensify a beam of radiation, the image intensifier comprising a photocathode configured to produce a flux of photoelectrons when exposed to the beam of radiation, the beam of radiation including essentially radiations in a selected spectral band, the photocathode including an intrinsic semiconductor layer and a p+ doped semiconductor layer, the intrinsic semiconductor layer substantially thicker than the p+ doped layer such that substantially all of the photoelectrons are produced in the intrinsic layer.

34. The intensifier of claim 33, wherein the photocathode further includes a n+ doped semiconductor layer and one or more dielectric layers, the one or more dielectric layers, the n+ doped semiconductor layer, the intrinsic semiconductor layer and the p+ doped semiconductor layer being constructed and arranged to form an optically coherent layer for the beam of radiation, the coherent layer adapted to produce standing waves within the intrinsic semiconductor layer.

35. The intensifier of claim 34, wherein the one or more dielectric layers are selected to reduce transmission of radiations in spectral bands outside the selected spectral band of the beam of radiation.

36. The intensifier of claim 33, further comprising a first and a second electrode to apply a voltage bias within the photocathode to migrate the photoelectrons from the intrinsic semiconductor layer toward the p+ doped semiconductor layer.

37. The intensifier of claim 36, wherein the first electrode is a metal electrode positioned proximate a first side of the p+ doped semiconductor layer, the intrinsic layer positioned on a second side of the p+ doped semiconductor layer.

38. The intensifier of claim 37, wherein the first electrode is a metal grid.

39. The intensifier of claim 38, wherein the metal grid has a metal surface area that is less than about 20% of a total surface area of the first side of the p+ doped semiconductor layer.

40. The intensifier of claim 39, wherein the metal grid is traversed by the flux of photoelectrons.

41. The intensifier of claim 36, wherein the second electrode includes a n+ doped semiconductor layer positioned on the intrinsic semiconductor layer.

42. The intensifier of claim 33, further comprising an insulating layer configured to reduce dark current generated in the intrinsic layer.

43. The intensifier of claim 42, wherein the insulating layer is positioned between the p+ doped semiconductor layer and a first electrode, the first electrode part of an electrode assembly that is adapted to apply a voltage bias within the photocathode to migrate the photoelectrons from the intrinsic semiconductor layer toward the p+ doped semiconductor layer.

44. The intensifier of claim 43, wherein the first electrode is a metal grid.

45. The intensifier of claim 44, wherein the metal grid is traversed by the flux of photoelectrons.