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| Flat optical TV screen |
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| X-Ray diagnostic installation |
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Active mirror wavefront sensor
| Details |
Inventors: Livingston, Peter M.; Shelton, Jean C.;
Assignee: TRW Inc. (Redondo Beach, CA)
Primary Examiner: Wan; Gene
Assistant Examiner:
Attorney, Agent or Firm: Heal; Noel F.
An interferometer, and corresponding method, for use in the measurement and correction of wavefront aberrations in a beam of radiation. The interferometer includes optical elements for generating a reference beam with a known wavefront phase characteristic. The reference beam is recombined with the sample beam, to produce an interference pattern indicative of the phase aberrations in the sample beam as compared with the reference beam. An array of detectors produces electrical signals corresponding to discrete elements of the detected pattern, and an electrical circuit for each elemental detector generates phase correction signals to be applied to a set of movable mirror elements arranged to effect phase changes in the sample beam path. The movable mirror elements adjust the elemental path lengths of the sample beam to yield zero detected phase differences. The mirror elements may be integrated into the interferometer, or may take the form of a deformable mirror used for phase compensation of a light beam. The reference beam in the preferred form of the invention is dithered at a high frequency to minimize the effect of noise, and each electrical circuit includes a synchronous detector to remove the dither-frequency component. In accordance with one disclosed form of the invention, the reference beam is not planar but is aberrated in a conjugate relationship with the radiation beam to be corrected, to provide improved control loop performance. |
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DETAILED DESCRIPTION The present invention in its broadest sense resides in a self-contained wavefront sensor capable of providing elemental wavefront phase difference signals over a large area or beam cross section.
Briefly, and in general terms, the apparatus of the invention comprises beam splitting means for splitting an input beam into a reference-arm beam and a sample beam, means for generating a non-aberrated reference beam from the reference-arm beam, and means for recombining the sample beam and the reference beam to produce an interference pattern.
The invention also includes means for modulating the reference beam with a high-frequency dither signal, multi-element detection means positioned to provide electrical signals indicative of the interference pattern, and multiple electrical circuits connected one to each detection means.
Each electrical circuit includes synchronous detector means for removing dither-frequency components, and integration means to provide a phase difference signal.
The apparatus also includes elemental deformable mirror means positioned to effect wavefront changes in the sample beam, and means for coupling the phase difference signals to the deformable mirror means.
Each element of the deformable mirror means is automatically adjusted to maintain a practically zero phase difference between the sample beam and the reference beam.
Since the device of the invention does not require complex numerical computations to reconstruct the wavefront, there is a significant cost advantage over prior interferometer systems, as well as an important speed advantage that permits the device to handle relatively large light beams without difficulty.
Since lateral shearing interferometers need at least two sets of slope measurements, in two orthogonal dimensions, the invention also provides at least a two-to-one advantage in numbers of component parts.
Moreover, since the device does not employ frequency multiplexing it is not limited, as are some multidither systems, in the number of mirror actuators it may drive
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LCD 
