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Method for improvidng the spatial resolution in an integrated adaptive optics apparatus
| Details |
Inventors: Pepper, David M.;
Assignee: Hughes Aircraft Company (Los Angeles, CA)
Primary Examiner: Moskowitz; Nelson
Assistant Examiner:
Attorney, Agent or Firm: Duraiswamy; V. D., Denson-Low; W. K.
Apparatus is disclosed for correcting wavefront errors in adaptive optics systems. A modified liquid crystal light valve is used as an integrated wavefront sensing and wavefront control system. A remote reference aberrated wavefront 10 first reflects off the liquid crystal substrate 20 and is then transferred by beam-splitters 14 and 15a, b and reflector 19 to the rear surface ofo the liquid crystal light valve 12. A one-to-one imaging system composed of lenses 70a, b and spatial filter 72 provide a new diffraction-limited optical transfer system which allows full use of the extremely high resolution capabilities of the liquid crystal light valve 12. The wavefront 10, after being imaged by the optical transfer system, is combined with a local reference plane 16, the interference pattern from which strikes the rear surface photoconductor 26. The photoconductor electrons liberated serve to alter the voltage across the liquid crystal at those points where the interference pattern has right maxima. Using a tunable birefringent liquid crystal layer 20, a voltage change causes a commensurate refractive index change in the liquid crystal substrate. These refractive index changes alter the optical path length of particular portions of the aberrated wavefront and the device's inherent negative feedback drives these phase errors to zero, at which point the wavefront 18 is completely corrected. A second laser beam 11 may be sent out of the device, reflecting off the corrective liquid crystal layer and predistorting it in order to correct for atmospheric path disturbances. The present invention provides an adaptive optics correction system possessing extraordinarily high spatial resolution. |
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DETAILED DESCRIPTION The present invention, by improving the resolving capability of a liquid crystal liquid valve adaptive optics system, accomplishes a major technological advancement by introducing an effective, compact, simple device which enables the active correction of aberrated wavefronts to a precision heretofore unattainable.
This invention utilizes a one-to-one imaging system in conjunction with a particular version of the liquid crystal light valve.
The resulting adaptive optics system performs with near-diffraction-limited resolution for wavefront sensing and correction.
If the usual liquid crystal element in a standard liquid crystal light valve (U.
S.
Pat.
No.
4,019,807, Hughes Model H-4060 with either a CdS or Si photoconductor) is replaced with a parallel-aligned tunable birefringent liquid crystal substrate, the device can be used as a deformable mirror.
The liquid crystal light valve device, however, requires no signal processing, no electrical amplifications, and no high-voltage sources.
It possesses a spatial resolution of approximately thirty microns per pixel.
In contrast, a typical deformable mirror might have 16 to 60 pixels spread over an area of 100 square centimeters.
Aberrated light from the target, degraded by all the distortions of its travel path, passes through the new liquid crystal element, reflects off a dielectric mirror, passes through the liquid crystal element once more, and is transferred by various optical means to the back side of the liquid crystal light valve where it combines with a locally generated unaberrated wavefront.
The two combined wavefronts create an interference pattern which through careful alignment is in exact registration with the incident target wavefront hitting the front side of the liquid crystal device.
A photoconductive layer lies sandwiched behind the liquid crystal element, both substrates being pressed between two clear conductive layers.
Once a voltage is placed across these conductors, any change in resistance in the photoconductor due to absorbed radiant energy engenders a commensurate change in voltage across the liquid crystal element at that point
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