Semiconductor generation of dynamic infrared images

• US 7,084,405 B1
• Filed: 05/07/2004
• Issued: 08/01/2006
• Est. Priority Date: 07/25/2003
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Murrer, Robert L. Jr., Bogatyrenko, Vyacheslav V., Malyutenko, Volodymyr K., Malyutenko, Oleg Y., Kircher, James R., Snyder, Donald R. III
• Primary Examiner(s): Gabor, Otilia
• Application Number:
  US10/845,609
• Time in Patent Office: 816 Days
• Field of Search: 250/370.08, 250/493.1
• US Class Current: 250/370.08
• CPC Class Codes: H04N 17/002 for television cameras
• 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 high-speed, high-resolution, broadband dynamic infrared scene generator based on semiconductor transducer conversion of visible spectrum scene images into infrared spectrum images. Wavelength conversion is accomplished in the semiconductor material through absorption of visible spectrum energy by valence electrons in a subsurface layer of the semiconductor material and photogeneration by valence band to conduction band electron transfer occurring within about one diffusion length of the semiconductor material surface. The semiconductor material used, for example Germanium or Silicon provides a band gap energy value that is smaller than the quantum energy level of the optical emission. Temperature of the semiconductor material may be maintained at a selected level above or below that of the infrared scene. Infrared images of higher frequency content than are achievable with conventional thermal heating infrared converters are accomplished. The invention thus includes down conversion of visible generated light in order to develop a semiconductor pixel-less Dynamic Infrared Scene Projector capable of simulating high-speed broadband IR scenery.

Claims

1. A semiconductor transducer based method of generating dynamic infrared images, said method comprising the steps of:

generating visible spectrum precursor images of said dynamic infrared images;

focusing said visible spectrum precursor images of said dynamic infrared images on an input image surface of a planar semiconductor transducer element;

collecting output dynamic infrared images from an output image surface of said planar semiconductor transducer element; and

input image surface to output image surface communication of said dynamic images within said planar semiconductor transducer element including a valence band to conduction band charged carrier photogeneration-recombination wavelength changing process.

2. The semiconductor transducer based method of generating dynamic infrared images of claim 1 wherein said semiconductor transducer element is characterized by the steps of:

absorbing energy quantums of said visible spectrum precursor images in valence band electrons located within a subsurface layer of said semiconductor material adjacent said input image surface; and

photogenerating and diffusing free charge carriers responsive to said visible spectrum absorbing step in a valence band to conduction band energy exchange located within a distance of substantially one diffusion length of said free charge carriers from said semiconductor material input image surface.

3. The semiconductor transducer based method of generating dynamic infrared images of claim 1 wherein said photogeneration-recombination wavelength changing process is characterized by a time constant of tens of microseconds.

4. The semiconductor transducer based method of generating dynamic infrared images of claim 1 wherein said step of focusing said visible spectrum precursor images of said dynamic infrared images on an input image surface of a planar semiconductor transducer element occurs on a first lateral surface of said semiconductor transducer element and said step of collecting output dynamic infrared images from an output image surface of said planar semiconductor transducer element occurs on an opposed second semiconductor transducer element lateral surface.

5. The semiconductor transducer based method of generating dynamic infrared images of claim 1 wherein said step of focusing said visible spectrum precursor images of said dynamic infrared images on an input image surface of a planar semiconductor transducer element occurs on a first lateral surface of said semiconductor transducer element and said step of collecting output dynamic infrared images from an output image surface of said planar semiconductor transducer element occurs on said same first lateral surface of said semiconductor transducer element.

6. The semiconductor transducer based method of generating dynamic infrared images of claim 1 further including one of the steps of:

maintaining said planar sample of semiconductor material at a selected operating temperature above a temperature representative of said infrared scene; and

maintaining said planar sample of semiconductor material at a selected operating temperature below a temperature representative of said infrared scene.

7. The semiconductor transducer based method of generating dynamic infrared images of claim 1 wherein said input image surface to output image surface communication of said dynamic images within said planar semiconductor transducer element includes communicating one of said visible spectrum precursor images and said output dynamic infrared images through a coating layer covering one of said input image surface and said output image surface of said planar semiconductor transducer element.

8. A broadband, high-speed, semiconductor material free-carrier-charge-based, method of generating dynamic infrared images, said method comprising the steps of:

disposing a planar sample of said semiconductor material along an optical axis extending through a source of visible image input data and an input surface of said semiconductor material;

locating an infrared image viewing apparatus proximate said optical axis adjacent one surface of said semiconductor material planar sample;

maintaining said planar sample of semiconductor material at a selected operating temperature; and

projecting a visible spectrum input optical radiation image of quantum energy level greater than a forbidden zone band-gap energy characteristic of said semiconductor material onto said semiconductor material input surface;

said projecting step enabling pumping of free carrier charges of said semiconductor material between valence band and conduction band energy states in a visible spectrum input optical image-controlled photogeneration-recombination broadband emission of infrared spectrum energy from said semiconductor material.

9. The broadband, high-speed, semiconductor material free-carrier-charge-based, method of generating dynamic infrared images of claim 8 wherein said planar sample of said semiconductor material is an optically flat polished sample of semiconductor material of selected surface recombination velocity characteristics.

10. The broadband, high-speed, semiconductor material free-carrier-charge-based, method of generating dynamic infrared images of claim 9 wherein said planar sample of said semiconductor material is an optically flat polished sample of homopolar Germanium semiconductor material.

11. The broadband, high-speed, semiconductor material free-carrier-charge-based, method of generating dynamic infrared images of claim 8 wherein said planar sample of said semiconductor material is disposed orthogonally with respect to said optical axis.

12. The broadband, high-speed, semiconductor material free-carrier-charge-based, method of generating dynamic infrared images of claim 8 wherein said planar sample of said semiconductor material is tilted toward said optical axis.

13. A method for achieving a dynamic infrared image generator transducer screen, said method comprising the steps of:

providing a wafer of semiconductor material having opposed lateral surfaces;

thermally diffusing said thin wafer to a selected n-impurity dopant hole charge carrier concentration;

said selected n-impurity dopant hole charge carrier concentration being sufficient to minimize absorption of background radiation and also achieve substantial transparency in said semiconductor material;

polishing first and second opposed surfaces of said thin wafer of semiconductor material to optical smoothness and flatness characteristics; and

mounting said thin wafer of semiconductor material in a temperature controlling fixture in reception of visible spectrum dynamic input images on one of said lateral surfaces and in emission of infrared spectrum output images on one of said lateral surfaces.

14. The method for achieving a dynamic infrared image generator transducer of claim 13 wherein said wafer of semiconductor material is comprised of Germanium of thickness between 0.1 and 4 millimeters thickness.

15. Dynamic infrared image generator apparatus comprising the combination of:

a source of dynamic visible spectrum images illumination;

a planar semiconductor material energy transducer screen element disposed in a focused location of said dynamic visible spectrum images illumination;

said semiconductor material of said energy transducer screen element having a bandgap energy value smaller than a quantum energy characteristic of said visible spectrum images illumination;

said semiconductor material of said energy transducer screen element having an n-impurity doping concentration level enabling minimum absorption of natural thermal radiation by free charge carriers within said semiconductor material;

temperature control apparatus located in thermal energy communication with said planar semiconductor material energy transducer screen element; and

infrared energy collection apparatus disposed adjacent an infrared energy output surface of said planar semiconductor material energy transducer screen element.

16. The dynamic infrared image generator apparatus of claim 15 wherein said temperature control apparatus located in thermal energy communication with said planar semiconductor material energy transducer screen element comprises one of a thermal cooling apparatus and a thermal heating apparatus.

17. The dynamic infrared image generator apparatus of claim 16 wherein said temperature control apparatus located in thermal energy communication with said planar semiconductor material energy transducer screen element comprises a source of electrical energy connected with said planar semiconductor material energy transducer screen element by electrical terminals received thereon and generating a heating electrical current flow in said planar semiconductor material energy transducer screen element.

18. The dynamic infrared image generator apparatus of claim 15 further including a radiant energy communicating coating layer disposed over one surface of said planar semiconductor material energy transducer screen element.

19. The dynamic infrared image generator apparatus of claim 18 further including first and second radiant energy communicating coating layers disposed over a radiant energy input first surface of said planar semiconductor material energy transducer screen element and a radiant energy output second surface of said planar semiconductor material energy transducer screen element.

20. The dynamic infrared image generator apparatus of claim 15 further including:

a background screen element disposed in parallel with one surface of said semiconductor material energy transducer screen element; and

a second temperature control apparatus disposed in thermal energy communication with said background screen element and maintaining said background screen element at a temperature lower than a surrounding background temperature.

21. The dynamic infrared image generator apparatus of claim 20 wherein said background screen element is comprised of a metallic plate and wherein said metallic plate includes an infrared energy absorbing coating located on a metallic plate surface adjacent said semiconductor material energy transducer screen element.

22. The dynamic infrared image generator apparatus of claim 15 wherein said semiconductor material energy transducer screen element is comprised of one of Germanium and Silicon semiconductor materials.

23. Dynamic infrared image generation apparatus comprising the combination of:

a planar sample of optical transducer semiconductor material having opposed flat surfaces and a valence band to conduction band free charge carrier photogeneration characteristic that is responsive to visible spectrum radiant energy;

a source of dynamic visible spectrum images focused on an input one of said optical transducer semiconductor material opposed flat surfaces;

said optical transducer semiconductor material having an energy bandgap characteristic smaller than a quantum energy characteristic of illumination comprising said dynamic visible spectrum images;

a collector of infrared images focused on an output one of said optical transducer semiconductor material opposed flat surfaces; and

temperature control apparatus disposed in thermal communication with said sample of optical transducer semiconductor material.

24. A broadband, high-speed, semiconductor material free-carrier-charge-based, method of generating dynamic infrared images, said method comprising the steps of:

disposing a planar transducer sample of said semiconductor material along an optical axis extending through a source of visible image input data and an input surface of said semiconductor material;

locating an infrared image viewing apparatus proximate said optical axis adjacent one surface of said semiconductor material planar transducer sample;

providing a planar background screen adjacent an input surface-opposed surface of said planar sample of semiconductor material, said background screen having a blackened surface adjacent said said planar transducer sample of semiconductor material;

maintaining said planar transducer sample of semiconductor material at a selected operating temperature;

cooling said background screen to an operating temperature below said selected operating temperature until a selected lowered background emission characteristic is achievable from said semiconductor material planar transducer sample; and

projecting a visible spectrum input optical radiation image of quantum energy level greater than a forbidden zone band-gap energy characteristic of said semiconductor material onto said semiconductor material input surface;

said projecting step enabling pumping of free carrier charges of said semiconductor material between valence band and conduction band energy states.

25. The broadband, high-speed, semiconductor material free-carrier-charge-based, method of generating dynamic infrared images of claim 24 wherein said projecting step pumping of free carrier charges of said semiconductor material between valence band and conduction band energy states includes a selected minemal background photogeneration-recombination pumping response.