Compensated coherent imaging for improved imaging and directed energy weapons applications

• US 7,405,834 B1
• Filed: 02/15/2006
• Issued: 07/29/2008
• Est. Priority Date: 02/15/2006
• Status: Active Grant

• Current Assignee: Lockheed Martin Coherent Technologies, Inc. (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Smith, Duane D., Embry, Carl W., Williams, Samuel G. L., Tucker, James Pete, Thomson, J. Alex, Oien, AnnMarie, Marron, Joseph C.
• Primary Examiner(s): Connolly; Patrick J
• Application Number:
  US11/354,449
• Time in Patent Office: 895 Days
• Field of Search: 356/450, 356/456, 356/484, 356/521
• US Class Current: 356/521
• CPC Class Codes: F41H 13/0062 causing structural damage to the target
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/499 using polarisation effects

Abstract

An imaging method and associated system for producing high-resolution images. The method includes illuminating an object or scene with coherent radiation such as beams from a laser and then, collecting scattered light with a plurality of subapertures rather than a single large aperture. The method continues with coherently detecting, such as with heterodyne detection, the scattered light to measure the complex amplitude incident on each subaperture and digitally reconstructing images from the coherently detected light for the subapertures. Then digital co-phasing is performed on the subapertures using an image sharpness or quality metric to form an image having the resolution of the total subaperture area. The method may also include determining an aimpoint in the formed image, calculating a phase screen, directing laser beams through the subapertures towards the aimpoint, and co-phasing the laser beams by applying the phase screen to form a single beam.

Claims

1. An imaging method for producing improved resolution images, comprising:

illuminating an object with coherent radiation;

with a plurality of subapertures, collecting light scattered from the illuminated object;

coherently detecting the light collected by each of the subapertures;

digitally reconstructing images from the coherently detected light for a set of the subapertures; and

digitally co-phasing the subapertures in the set of the subapertures using an image sharpness metric to form an image of the object comprising the digitally reconstructed images.

2. The method of claim 1, wherein the coherently detecting comprises measuring the complex amplitude on each of the subapertures and the constructed image has substantially a resolution of a total area of the subaperatures in the set.

3. The method of claim 1, wherein the set of subapertures comprises all of the plurality of subapertures.

4. The method of claim 1, wherein the subapertures are arranged in a regular array or in an irregular array.

5. The method of claim 1, wherein the illuminating comprises operating a laser to produce the coherent radiation in the form of laser light at or below a wavelength of about 10 microns.

6. The method of claim 1, wherein the coherently detecting comprises spatial heterodyne detection, temporal heterodyne detection, or quadrature detection.

7. The method of claim 1, wherein the coherently detecting comprises detection of glint, the glint being provided by transmission of a beacon or derived from an illuminated feature in the field of view of the subapertures.

8. The method of claim 1, wherein the coherently detecting comprises detection of glint, wherein the glint is located in the field of view of the subapertures and the coherently detecting comprises using the located glint as local oscillator beam input.

9. The method of claim 1, wherein the image sharpness metric is the sum of square of intensities of the coherently detected light or is the sum of higher order power of the intensities of the coherently detected light.

10. The method of claim 1, wherein the co-phasing comprises:

using a pairwise algorithm to co-phase all of the subapertures in the set;

altering relative tip, tilt, and/or piston, and/or higher order phase aberrations for each of the subaperatures in the set to enhance the image sharpness metric;

applying co-phasing corrections to different areas of the field of view to correct for anisoplanatism;

using a steepest descent algorithm;

using a simplex method; and

/or compensating for geometric alignment of the apertures in the set.

11. The method of claim 1, further comprising:

identifying an aimpoint within the formed image;

determining a phase screen for the aimpoint;

directing a multiplicity of laser beams through the subapertures towards the aimpoint; and

co-phasing the multiplicity of laser beams by applying the phase screen to the laser beams propagating through the subapertures to form a high power laser beam.

12. The method of claim 11, further comprising firing the high power laser beam to illuminate a portion of the object.

13. The method of claim 11, wherein the laser beams are provided by lasers selected from the group consisting of 1 micron lasers, 1.5 micron lasers, and 10 micron lasers.

14. The method of claim 11, wherein corrections are applied to different areas of the field of view to correct for anisoplanatism.

15. The method of claim 11, wherein the multiplicity of laser beams are derived from a single laser.

16. An imaging system comprising:

a laser for illuminating a field of view;

a plurality of subaperture transceivers for receiving and detecting light scattered from the field of view using coherent detection; and

a processing system for calculating a complex electric field at a set of the subaperture transceivers and for forming an image.

17. The imaging system of claim 16, wherein the processing system is further operable for determining a target point in the formed image, and wherein the imaging system further comprises a high-energy laser for outputting a high energy laser beam through the subaperture transceivers toward the target point.

18. The imaging system of claim 17, further comprising a laser beam distorter distorting the output high energy laser beam such that the distorted high energy laser beam arrives at the target point with a substantially diffraction-limited footprint.

19. An imaging method for producing high-resolution images, comprising:

illuminating an object with coherent radiation from a laser;

with a plurality of subapertures, collecting light scattered from the illuminated object;

coherently detecting the light collected by each of the subapertures using heterodyne detection; and

digitally co-phasing the subapertures in the set of the subapertures using an image sharpness metric to form an image of the object having substantially the resolution of the total area of all the subapertures in the set.

20. The method of claim 19, further comprising identifying an aimpoint in the formed image, directing a plurality of laser beams through the subapertures in a direction opposite the collected light, co-phasing the plurality of laser beams into substantially a single beam, and firing the single beam at the aimpoint.