Stitching of near-nulled subaperture measurements
First Claim
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1. A method of expanding the operating range of a metrology system for measuring aspheric test objects comprising steps of:
- associating an optical wavefront propagator with a physical test object in a plurality of different relationships for conveying optical measurement wavefronts to the test object;
acquiring partially overlapping optical wavefront measurements of the test object in each of the different relationships by measuring shapes of the measurement wavefronts with an optical wavefront-measuring gauge having a limited capture range of wavefront shapes;
reshaping the measurement wavefront into an aspheric form with a variable optical aberrator between a limited number of the measurements in the different relationships to maintain the measurement wavefront within the capture range of the wavefront-measuring gauge;
incorporating compensators in an operation for assembling the partially overlapping measurements into a composite measurement, andacquiring values for the compensators in the operation for reducing differences between overlapping portions of the measurements that are at least partially attributable to the reshaping of the measurement wavefront by the variable optical aberrator.
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Abstract
A metrology system for measuring aspheric test objects by subaperture stitching. A wavefront-measuring gauge having a limited capture range of wavefront shapes collects partially overlapping subaperture measurements over the test object. A variable optical aberrator reshapes the measurement wavefront with between a limited number of the measurements to maintain the measurement wavefront within the capture range of the wavefront-measuring gauge. Various error compensators are incorporated into a stitching operation to manage residual errors associated with the use of the variable optical aberrator.
9 Citations
30 Claims
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1. A method of expanding the operating range of a metrology system for measuring aspheric test objects comprising steps of:
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associating an optical wavefront propagator with a physical test object in a plurality of different relationships for conveying optical measurement wavefronts to the test object; acquiring partially overlapping optical wavefront measurements of the test object in each of the different relationships by measuring shapes of the measurement wavefronts with an optical wavefront-measuring gauge having a limited capture range of wavefront shapes; reshaping the measurement wavefront into an aspheric form with a variable optical aberrator between a limited number of the measurements in the different relationships to maintain the measurement wavefront within the capture range of the wavefront-measuring gauge; incorporating compensators in an operation for assembling the partially overlapping measurements into a composite measurement, and acquiring values for the compensators in the operation for reducing differences between overlapping portions of the measurements that are at least partially attributable to the reshaping of the measurement wavefront by the variable optical aberrator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of assembling a composite measurement of a physical test object from a plurality of partially overlapping measurements of the test object comprising steps of:
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acquiring a plurality of partially overlapping data maps measuring a physical property of the test object from a test wavefront that encounters the test object, each data map being extracted from a shape of the test wavefront referenced against a datum; relatively changing the shape of the test wavefront into an aspheric form with respect to the datum independently of the test object between acquisitions of a limited number of the data maps to reduce differences between the shape of the test wavefront and the datum, including relatively changing the shape of the measurement wavefront to include at least one of astigmatism, coma, and trefoil; evaluating overlapping regions of the data maps to characterize the relative change in the wavefront shape between acquisitions of the data maps; and modifying the data maps in accordance with the characterization of the relative change in the wavefront shape between measurements for assembling the partially overlapping data maps into a composite data map. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22)
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23. A method of assembling a composite measurement of a physical test object from a plurality of subaperture measurements of the test object comprising steps of:
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generating an optical measurement wavefront, propagating the measurement wavefront through encounters with both a variable optical aberrator and the physical test object en route to a wavefront-measuring gauge having a limited capture range of wavefront shapes; stepping an axis of an optical wavefront propagator relative to an axis of the physical test object through a succession of off-axis positions between the wavefront propagator and the test object, the wavefront propagator being arranged for conveying the measurement wavefront to the test object; adjusting the variable optical aberrator between a limited number of the off-axis positions for maintaining the shape of the measurement wavefront within the capture range of the wavefront-measuring gauge; collecting partially overlapping subaperture measurements of the test object with the wavefront-measuring gauge at the succession of off-axis positions; modeling effects of the variable optical aberrator on the subaperture measurements; evaluating mismatched measurements within overlapping portions of subaperture measurements to further characterize effects of the variable optical aberrator on the subaperture measurements, including changing values of variables within the model to reduce the mismatched measurements within overlapping portions of subaperture measurements; and stitching the subaperture measurements of the test object together into a composite measurement while discounting the characterized effects of the variable optical aberrator on the subaperture measurements. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30)
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Specification