Solid cryogenic optical filter

• US 6,444,984 B1
• Filed: 08/11/2000
• Issued: 09/03/2002
• Est. Priority Date: 08/11/2000
• Status: Expired due to Term

• Current Assignee: DRS Network & Imaging Systems, LLC (Leonardo S.p.A.)
• Original Assignee: DRS Sensors & Targeting Systems, Inc. (Leonardo S.p.A.)
• Inventors: Dadson, Carl F., Lundgren, Mark A.
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US09/637,383
• Time in Patent Office: 753 Days
• Field of Search: 250/339.03, 250/338.1, 250/339.01, 359/586, 359/589
• US Class Current: 250/339.03
• CPC Class Codes: G01J 5/061 by controlling the temperature of the apparatus or parts thereof, e.g. using cooling means or thermostats

Abstract

An optical filter system is described wherein a fluid, such as gaseous phases of water or carbon dioxide, is frozen onto a transmissive substrate positioned in the optical path of an infrared sensor system. The frozen material, which is preferably maintained at cryogenic temperatures, acts as a natural optical filter, absorbing certain undesirable wavelength bands of atmospheric infrared radiation, thus preventing them from reaching the detector of the sensor system. Simultaneously, the optical filter system allows certain desirable wavelength bands of infrared radiation to be transmitted, thus permitting them to reach the detector of the sensor system. The overall effect is to reduce the amount of noise and clutter generated by the undesirable atmospheric infrared radiation from reaching the detector of the sensor system, thus increasing the resolution and effectiveness of the sensor system.

Claims

1. An optical filter, comprising:

a substrate transmissive to infrared radiation, wherein the infrared radiation includes at least two different wavelength bands; and

an erasable layer of material formed on at least a portion of a surface of the transmissive substrate, wherein the material substantially absorbs at least one of the at least two different wavelength bands of the infrared radiation so as to substantially prevent the transmission of one of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

2. The invention of claim 1, wherein the material permits the transmission of the other of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

3. The invention of claim 1, wherein the material is introduced in fluid form adjacent to the transmissive substrate and subsequently frozen so as to form the layer of material on the at least a portion of the surface of the transmissive substrate.

4. The invention of claim 3, wherein the fluid is selected from the group consisting of gaseous phases of water, carbon dioxide, and combinations thereof.

5. The invention of claim 1, wherein the material is selected from the group consisting of solid phases of water, carbon dioxide, and combinations thereof.

6. The invention of claim 1, wherein the material is maintained at a cryogenic temperature.

7. The invention of claim 1, wherein the erasable layer of material is erased from the portion of the surface of the transmissive substrate upon exposure to a predetermined environment selected from the group consisting of a predetermined temperature, at predetermined pressure, a predetermined erasing material, and combinations thereof.

8. An optical filter system, comprising:

an optical system for focusing infrared radiation, wherein the infrared radiation includes at least two different wavelength bands;

a substrate transmissive to the infrared radiation; and

an erasable layer of material formed on at least a portion of a surface of the transmissive substrate, wherein the material substantially absorbs at least one of the at least two different wavelength bands of the infrared radiation so as to substantially prevent the transmission of one of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

9. The invention of claim 8, further comprising an infrared radiation sensor system in communication with the transmissive substrate.

10. The invention of claim 9, further comprising a signal processing system in communication with the infrared radiation sensor system.

11. The invention of claim 8, wherein the material permits the transmission of the other of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

12. The invention of claim 8, wherein the material is introduced in fluid form adjacent to the transmissive substrate and subsequently frozen so as to form the layer of material on the at least a portion of the surface of the transmissive substrate.

13. The invention of claim 12, wherein the fluid is selected from the group consisting of gaseous phases of water, carbon dioxide, and combinations thereof.

14. The invention of claim 8, wherein the material is selected from the group consisting of solid phases of water, carbon dioxide, and combinations thereof.

15. The invention of claim 8, wherein the material is maintained at a cryogenic temperature.

16. The invention of claim 8, wherein the erasable layer of material is erased from the portion of the surface of the transmissive substrate upon exposure to a predetermined environment selected from the group consisting of a predetermined temperature, a predetermined pressure, a predetermined erasing material, and combinations thereof.

17. An infrared detection system, comprising:

an optical system for focusing infrared radiation, wherein the infrared radiation includes at least two different wavelength bands;

a substrate transmissive to the infrared radiation;

an erasable layer of material formed on at least a portion of a surface of the transmissive substrate, wherein the material substantially absorbs at least one of the at least two different wavelength bands of the infrared radiation so as to substantially prevent the transmission of one of the at least two different wavelength bands of the infrared radiation through the transmissive substrate; and

an infrared radiation sensor system in communication with the transmissive substrate.

18. The invention of claim 17, further comprising a signal processing system in communication with the infrared radiation sensor system.

19. The invention of claim 17, wherein the material permits the transmission of the other of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

20. The invention of claim 17, wherein the material is introduced in fluid form adjacent to the transmissive substrate and subsequently frozen so as to form the layer of material on the at least a portion of the surface of the transmissive substrate.

21. The invention of claim 20, wherein the fluid is selected from the group consisting of gaseous phases of water, carbon dioxide, and combinations thereof.

22. The invention of claim 17, wherein the material is selected from the group consisting of solid phases of water, carbon dioxide, and combinations thereof.

23. The invention of claim 17, wherein the material is maintained at a cryogenic temperature.

24. The invention of claim 17, wherein the erasable layer of material is erased from the portion of the surface of the transmissive substrate upon exposure to a predetermined environment selected from the group consisting of a predetermined temperature, a predetermined pressure, a predetermined erasing material, and combinations thereof.

25. An optical filter, comprising:

a substrate transmissive to infrared radiation, wherein the infrared radiation includes at least two different wavelength bands; and

a layer of material formed on at least a portion of a surface of the transmissive substrate, wherein the material substantially absorbs at least one of the at least two different wavelength bands of the infrared radiation so as to substantially prevent the transmission of one of the at least two different wavelength bands of the infrared radiation through the transmissive substrate, wherein the material is introduced in fluid form adjacent to the transmissive substrate and subsequently frozen so as to form the layer of material on the at least a portion of the surface of the transmissive substrate.

26. The invention of claim 25, wherein the material permits the transmission of the other of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

27. The invention of claim 25, wherein the fluid is selected from the group consisting of gaseous phases of water, carbon dioxide, and combinations thereof.

28. The invention of claim 25, wherein the material is selected from the group consisting of solid phases of water, carbon dioxide, and combinations thereof.

29. The invention of claim 25, wherein the material is maintained at a cryogenic temperature.

30. An optical filter system, comprising:

an optical system for focusing infrared radiation, wherein the infrared radiation includes at least two different wavelength bands;

a substrate transmissive to the infrared radiation; and

a layer of material formed on at least a portion of a surface of the transmissive substrate, wherein the material substantially absorbs at least one of the at least two different wavelength bands of the infrared radiation so as to substantially prevent the transmission of one of the at least two different wavelength bands of the infrared radiation through the transmissive substrate, wherein the material is introduced in fluid form adjacent to the transmissive substrate and subsequently frozen so as to form the layer of material on the at least a portion of the surface of the transmissive substrate.

31. The invention of claim 30, further comprising an infrared radiation sensor system in communication with the transmissive substrate.

32. The invention of claim 31, further comprising a signal processing system in communication with the infrared radiation sensor system.

33. The invention of claim 30, wherein the material permits the transmission of the other of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

34. The invention of claim 30, wherein the fluid is selected from the group consisting of gaseous phases of water, carbon dioxide, and combinations thereof.

35. The invention of claim 30, wherein the material is selected from the group consisting of solid phases of water, carbon dioxide, and combinations thereof.

36. The invention of claim 30, wherein the material is maintained at a cryogenic temperature.

37. An infrared detection system, comprising:

an optical system for focusing infrared radiation, wherein the infrared radiation includes at least two different wavelength bands;

a substrate transmissive to the infrared radiation;

a layer of material formed on at least a portion of a surface of the transmissive substrate, wherein the material substantially absorbs at least one of the at least two different wavelength bands of the infrared radiation so as to substantially prevent the transmission of one of the at least two different wavelength bands of the infrared radiation through the transmissive substrate, wherein the material is introduced in fluid form adjacent to the transmissive substrate and subsequently frozen so as to form the layer of material on the at least a portion of the surface of the transmissive substrate; and

an infrared radiation sensor system in communication with the transmissive substrate.

38. The invention of claim 37, further comprising a signal processing system in communication with the infrared radiation sensor system.

39. The invention of claim 37, wherein the material permits the transmission of the other of the at least two different wavelength bands of the infrared radiation through the transmissive substrate.

40. The invention of claim 37, wherein the fluid is selected from the group consisting of gaseous phases of water, carbon dioxide, and combinations thereof.

41. The invention of claim 37, wherein the material is selected from the group consisting of solid phases of water, carbon dioxide, and combinations thereof.

42. The invention of claim 37, wherein the material is maintained at a cryogenic temperature.