Optics: measuring and testing – Lamp beam direction or pattern
Patent
1991-10-07
1994-03-15
Rosenberger, Richard A.
Optics: measuring and testing
Lamp beam direction or pattern
2502019, G01J 100
Patent
active
052949710
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a wave front sensor.
Known wave front sensors operate by interferometry or holography. These are sensitive to environmental influences, such as temperature changes.
The testing of objectives by the Hartmann test, known, for example, from German patent document DE 3,318,293 A1, scans the objective aperture with one or more beams which are masked out by a movable perforated diaphragm with one or more perforations and employs a space-sensitive detector. In particular a photographic fim is disposed in front of, or behind, the focal plane. In the case of a plurality of perforations as in German patent document (DE 3,318,293 A1), the detector is disposed and designed so that signals associated with the individual perforations are recorded separately.
In D. Malacara, Optical Shop Testing, Chapter 10 I, "Ghozeil, Hartmann and Other Screen Tests," pp. 323 et seq., Wiley New York 1978, the Hartmann Test is described in terms of variants. The analytical theory is also described.
Optical multiplex processes using code matrices according to Hadamard are described in M. Hewitt and N. J. A. Sloane, Hadamard Transform Optics, Academic Press, New York, 1979, for spectrometers and image analysis systems. Using these processes, it is possible to achieve substantial noise suppression.
The object of the invention is to provide an efficient and robust low-noise wave front sensor by which the amplitude and phase of the wave front can be determined. It is then also possible to determine from this the remote radiation field of the wave.
This is achieved by a wave front sensor having a focusing optical system, a diaphragm with a plurality of perforations, situated simultaneously in the beam path in an encoded arrangement, a device for advancing the perforated diaphragm, so that a multiplicity of different encoded arrangements of perforations are situated in succession in the beam path and the entire cross section of the beam path is repeated scanned overall with different encoded arrangements of perforations, a space-resolving light detector, which is disposed close to the focal plane of the optical system and which determines in each instance the position and intensity of the light spot which results from the superposition of the plurality of beams generated by the perforations, so that a multiplex effect arises, and a storage and computing unit, which reconverts the position and intensity values determined by the light detector using the code of the arrangement of the perforations, into the phase and amplitude of the wave front.
The invention is explained with the aid of the drawings, in which:
FIG. 1 diagrammatically shows the overall construction of a wave front sensor.
FIG. 2 shows a variant with a telecentric optical system, and a rotating disk as the carrier of the perforated diaphragm.
FIGS. 3a and 3b show a disk with a perforated diaphragm according to a cyclic Hadamard code with a radial arrangement of perforations.
FIG. 4 shows a disk with perforated diaphragms which form orthogonally encoded regions.
The wave front sensor shown in FIG. 1 includes a highly corrected focusing optical system 1, represented as a simple converging lens, a perforated diaphragm 2 which exhibits in the parallel beam path 3 corresponding to the wave front 31 a plurality of perforations 21 which are disposed in an encoded configuration and, in the focal plane 4 (spacing f from the principal plane of the lens) a high spatial resolution light detector 41.
The beams 32 passing through the perforations 21 have their real focus dependent upon disturbance of the wave front 31 at locations which deviate from the ideal focus. However, they are superposed on the detector 41 to form a light spot 33. The detector 41 is chosen to be of such a size that the entire light spot which is formed when the perforated diaphragm 2 is removed can be detected in its entirety. This gives a multiplex effect and the noise suppression associated therewith. A suitable detector 41 is a lateral detector of the SITEK 2L4 type, with a 4.times.4 mm.sup.2
REFERENCES:
patent: H615 (1989-04-01), Feinleib et al.
patent: 4141652 (1979-02-01), Feinleib
patent: 4438330 (1984-03-01), Hardy
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patent: 4641962 (1987-02-01), Sueda et al.
patent: 4824243 (1989-04-01), Wheeler et al.
Optical Engineering, "Coded Aperture Imaging: Many Holes Make Light Work", vol. 19 No. 3, pp. 283-289, May/Jun. 1980, Cannon et al.
"Hartmann and Other Screen Tests" pp. 323-334, I. Ghozeil.
Analytical Chemistry, "A Thousand Points of Light: The Hadamard Transform", vol. 61, No. 11, Jun. 1989 pp. 724A-734A, Treado et al.
M. Harwit et al., "Hadamard Transform Optics", Academic Press, 1979.
Braunecker Bernhard
Gaechter Bernhard
Huiser, deceased Andre
Leica Heerbrugg AG
Pham Hoa Q.
Rosenberger Richard A.
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