Apparatus and techniques for enhanced resolution imaging
Disclosed are systems and methods for synthesizing a high resolution image associated with a large imaging aperture using an optical imaging apparatus having a smaller aperture. In certain implementations, introduction of a coherent homodyne reference beam to a coherent imaging of an object can result in formation of a Fourier space side lobe that includes information about a portion of a spectrum representative of the object's Fourier spectrum. Images can be obtained at a number of different orientations to yield a number of such side lobe images so as to allow construction of the object's spectrum. A synthesized image corresponding to such a constructed spectrum can have an improved resolution that exceeds the performance limit imposed by the aperture of the optical imaging apparatus.
1. A method for imaging, the method comprising:
forming a collective image, the forming comprising:
providing an illumination beam to an object so as to yield interaction light resulting from interaction between the illumination beam and the object;
directing at least some of the interaction light as an imaging beam to an imaging sensor so as to form an image of the object on the imaging sensor; and
interfering at least a portion of the interaction light with a reference beam thereby forming an interference pattern imaged on the image sensor, the interference pattern combining with the image of the object at the imaging sensor to form the collective image having a Fourier transform that includes a side lobe in Fourier space, the side lobe having phase information about a range of the object's spatial frequencies; and
repeating the forming at different orientations between the imaging beam and the object until a plurality of collective images are obtained, each of the collective images having a different range of the object's spatial frequency.
2. The method of claim 1 , further comprising generating and extracting a side lobe to yield a sub-aperture for each of the plurality of collective images.
3. The method of claim 2 , wherein the generating of the side lobe comprises applying a Fourier transform to the collective image.
4. The method of claim 2 , further comprising combining the sub-apertures to yield a synthesized aperture.
5. The method of claim 4 , further comprising generating an intensity image corresponding to the synthesized aperture.
6. The method of claim 5 , wherein the intensity image has a resolution that exceeds the resolution capability associated with each sub-aperture.
7. The method of claim 4 , wherein each of the sub-apertures resulting from the collective images overlaps with one or more of its neighboring sub-apertures.
8. The method of claim 7 , wherein the combining comprises:
selecting a first sub-aperture;
identifying a region of overlap in phases of the first sub-aperture and a second sub-aperture;
calculating a difference in the phases within the region of overlap; and
adjusting the phase of the second sub-aperture based on the calculated difference to yield an adjusted phase for the second sub-aperture that is substantially in phase with the first aperture.
9. The method of claim 8 , wherein the combining further comprises repeating the identifying, calculating, and adjusting with one or more sub-apertures relative to one or more of the first and second sub-apertures.
10. The method of claim 9 , wherein the combining further comprises selecting phase-adjusted sub-apertures that represent substantially contiguous ranges of the object's spatial frequency to form the synthesized aperture.
11. The method of claim 1 , wherein the reference beam comprises a coherent light beam.
12. The method of claim 11 , wherein the reference beam originates from a source that also generates the illumination beam.
13. The method of claim 12 , wherein the reference beam is separated from the illumination beam and provided to the imaging sensor.
14. The method of claim 11 , wherein the reference beam originates from the interaction light.
15. The method of claim 1 , wherein the illumination beam comprises a coherent light beam.
16. The method of claim 15 , wherein the coherent beam comprises a laser beam.
17. The method of claim 16 , wherein the laser beam includes a frequency in a visible spectrum.
18. The method of claim 1 , wherein the different orientations between the imaging beam and the object are introduced by moving an aperture that the imaging beam passes through along a direction having a lateral component relative to the imaging beam's optical axis.
19. The method of claim 1 , wherein the different orientations between the imaging beam and the object result from rotating the object relative to the imaging beam.
20. The method of claim 1 , wherein the different orientations between the imaging beam and the object result from moving a platform on which the image sensor is disposed.
21. The method of claim 1 , further comprising recording the plurality of collective images so as to allow subsequent retrieval and analysis of the collective images.
22. The method of claim 1 , wherein interaction between the illumination bean and the object comprises reflection of the illumination beam from the object.
23. The method of claim 1 , wherein at least one of the actions recited is performed by one or more processors.
24. The method of claim 1 , further comprising using one or more non-transitory computer readable media comprising computer instructions to cause one or more computer processors to generate an image having a resolution higher than the resolution of said collective images by using information obtained from said plurality of collective images.
25. An imaging system, comprising:
a coherent light source configured to generate an illumination beam;
an optics assembly configured to deliver the illumination beam from the coherent light source to an object and to gather interaction light from interaction between the illumination beam and the object and form an image of the object; and
an imaging sensor positioned and configured to allow recording of the image,
wherein the optics assembly is further configured to provide a reference beam to the image sensor, the reference beam combining with the image of the object at the imaging sensor to form a collective image having a Fourier transform that includes a side lobe in Fourier space, the side lobe having phase information about a range of the object's spatial frequency.
26. The system of claim 25 , further comprising a non-transitory computer readable medium configured to allow storage of the collective images.
27. The imaging system of claim 26 , further comprising a controller configured to control acquisition of a plurality of different collective images.
28. A movable craft having the imaging system of claim 25 .
29. The movable craft of claim 28 , wherein the movable craft includes an aircraft, a spacecraft, a watercraft, or a landcraft.