Computer generated hologram (ICGH) null
View Patent ↗An optical testing system includes a computer generated hologram (CGH) and an imaging element (IE). Both are disposed in a path of light traveling between a wavefront measuring system (WMS) and an object under test. The CGH is located a first distance from the WMS and the IE is located a second distance from the WMS. The IE is further away from the WMS, than the CGH is from the WMS, along the path of light. The center of curvature (CoC) of the object under test is also disposed in the path of light, in which the CoC is located a third distance from the WMS. The third distance is larger than the second distance, along the path of light. The IE forms an image of the object under test at the CGH; and the CGH is configured to provide a null wavefront for the image of the object under test at the CGH. The null wavefront is received by the WMS. Moreover, the IE of the optical testing system may include an imaging lens having a planar surface facing away from the CGH and a convex surface facing toward the CGH. The IE may also include an imaging mirror.
1. An optical testing system comprising
a computer generated hologram (CGH) and an imaging element (IE), both disposed in a path of light traveling between a wavefront measuring system (WMS) and an object under test, and
the CGH is located a first distance from the WMS and the IE is located a second distance from the WMS,
wherein the second distance is larger than the first distance,
the IE is positioned to form an image of the object under test at the CGH,
the CGH is positioned to provide a null wavefront for the image of the object under test at the CGH, and
the null wavefront is received by the WMS.
2. The optical testing system of claim 1 wherein
a center of curvature (CoC) of the object under test is disposed in the path of light,
the CoC is located a third distance from the WMS, and
the third distance is larger than the second distance.
3. The optical testing system of claim 1 wherein
the WMS includes an interferometer, and
an entrance port of the interferometer is configured to form a pupil image of the object under test.
4. The optical testing system of claim 1 wherein
the IE includes an imaging lens having a flat surface facing away from the CGH and a convex surface facing toward the CGH.
5. The optical testing system of claim 1 wherein
the object under test includes a surface of a primary mirror, or a surface of a tertiary mirror.
6. The optical testing system of claim 1 wherein
the path of light is formed along an axial dimension, and
a collimated beam passes through the CGH and enters an entrance port of the WMS.
7. The optical testing system of claim 1 wherein
the CGH includes gratings shaped as rings formed about a center point, and
the density of the rings increases monotonically as distance increases from the center point.
8. The optical testing system of claim 1 wherein
the IE is either an imaging mirror or an imaging lens,
when the IE is an imaging mirror, then the CGH reflects light, and
when the IE is an imaging lens, then the CGH passes the light.
9. An improved computer generated hologram (ICGH) comprising
a CGH and an imaging element (IE)), both disposed in a path of light traveling between a wavefront measuring system (WMS) and an object under test, and
the CGH is located a first distance from the WMS and the IE is located a second distance from the WMS,
wherein the second distance is larger than the first distance,
the IE is postioned to form an image of the object under test at the CGH,
the CGH is positioned to provide a null wavefront for the image of the object under test at the CGH, and
the null wavefront is received by the WMS.
10. The ICGH of claim 9 wherein
a center of curvature (CoC) of the object under test is disposed in the path of light,
the CoC is located a third distance from the WMS, and
the third distance is larger than the second distance.
11. The ICGH of claim 9 wherein
the WMS includes an interferometer, and
an entrance port of the interferometer is configured to form a pupil image of the object under test.
12. The ICGH of claim 9 wherein
the IE includes an imaging lens having a flat surface facing away from the CGH and a convex surface facing toward the CGH.
13. The ICGH of claim 9 wherein
the object under test includes a surface of a primary mirror, or a surface of a tertiary mirror.
14. The ICGH of claim 9 wherein
the path of light is located along an axial dimension, and
a collimated beam is formed between the CGH and an entrance port of the WMS.
15. The ICGH of claim 9 wherein
the CGH includes gratings shaped as rings formed about a center point, and
the density of the rings increases monotonically as distance increases from the center point.
16. The optical testing system of claim 9 wherein
the IE is either an imaging mirror or an imaging lens,
when the IE is an imaging mirror, then the CGH reflects light, and
when the IE is an imaging lens, then the CGH passes the light.
17. A method of testing an optical surface of an object comprising the steps of:
placing a computer generated hologram (CGH) and an imaging element (IE) in a path of light between a wavefront measuring system (WMS) and the surface of the object;
locating the CGH at a first distance from the WMS and the IE at a second distance from the WMS, where the second distance is larger than the first distance;
forming an image of the object at the position of the CGH; and
testing optical properties of the surface of the object by the WMS.
18. The method of claim 17 further including the steps of:
placing a center of curvature (CoC) of the surface of the object in the path of light; and
locating the CoC a third distance from the WMS, where the third distance is larger than the second distance.
19. The method of claim 17 wherein
the IE includes two opposing surfaces, one flat surface and the other a convex surface.