New catadioptric design type fast speed and wide field
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The document introduces a novel optical design featuring an f/1.0 catadioptric telecentric system with a 65-degree field of view and an external pupil for enhanced image quality and color correction. This design utilizes a flat metasurface with altered dispersion to improve monochromatic and polychromatic performance while mitigating residual color issues. Ultimately, it asserts that advancements in metasurface technology are crucial for achieving high-performance optical systems with simultaneous fast speeds and wide fields of view.
New catadioptric design type fast speed and wide field
- 1. An f/1.0 catadioptric telecentric design with a 65 degree field and an external pupil Dave Shafer David Shafer Optical Design Fairfield, CT 06824 203-259-1431 shaferlens@sbcglobal.net
- 2. There is a new type of design, described here, which pushes the boundaries of what is possible in high performance optical designs. It is simple, with just a few elements Fast f# speed, like f/1.0 Wide field of view Telecentric at the image Has an external pupil that could be used for scanning Very high image quality Excellent color correction All of these features are simultaneously present. The excellent color correction in this simple system can only be achieved by using a flat metasurface with slightly altered dispersion.
- 3. This new type of design is based on altering an existing very high performance design in an important way that opens up a new class of designs with many possible applications. The new design was developed while looking for something that can only be done by using a metasurface. In particular, it requires a metasurface with slightly altered dispersion to give excellent color correction to a design. The previous design that this new design is based on is shown next. It is a 4x magnification design with finite conjugates. The new design has, by contrast, collimated input.
- 4. My 2005 catadioptric design (US patent 7385756 – shown here) that I did for Zeiss led to new high NA catadioptric designs which are the basis of the current state-of-the-art lithographic tools. All of today’s leading edge computer chips are made with a 1.35 NA immersion catadioptric design. The most important features of these designs are at least one intermediate image and the use of mirrors to correct Petzval curvature of the image.
- 5. Outer field angle boundary with no vignetting Inner field angle boundary with no vignetting Image size with no vignetting, and an empty center (due to holes in the mirrors) The simplest possible design of this type, with collimated input, has two aspheric mirrors and one aspheric lens. For a 25 mm focal length it is diffraction-limited, monochromatically at .55u, at f/3.5 over a 34 degree field diameter with a 14 degree blank center. More complexity is needed to get a faster f# speed. 34 degree outer field diameter 14 degree inner field diameter
- 6. A 4.5 X 25 degree strip field can be fit inside the unvignetted annular field of the design Two of these could work with the same design at the same time, maybe for two different wavelengths or different polarizations. To get a faster f# speed with diffraction-limited performance we need to add one lens to the design, as will be shown.
- 7. A long field size in the out of plane direction here does not affect the rays/mirrors clearances in the plane of the page. Aperture stop/ pupil The design is best suited to long rectangular out of the plane fields
- 8. Adding one lens makes a big difference – for the same 25 mm focal length then it can be diffraction-limited over a 47 degree diameter field at f/2.0 while still being a very simple design. All the surfaces are aspheric to get the best performance.
- 9. Half of picture Full picture New lens 6 X 35 degrees strip field, or 15 X 15 degree square field, at f/2.0 25 mm focal length diffraction-limited at .55u over a 47 degree diameter field at f/2.0 2 aspheric mirrors, 2 aspheric lenses
- 10. It should have been obvious to me that my lithographic design could be adapted to work with collimated input and have a wide range of fast speed and wide angle imaging uses. But like most new ideas, such as this pet door for cars, it is only obvious after you have seen it.
- 11. Same field size as before (47 degree diameter) but now f/1.5 instead of f/2.0, due to an extra lens. Still diffraction - limited over the field. New lens These have been designs with a single intermediate image. To get to faster f# speeds like f/1.0 and wider fields of view we need to go to two intermediate images, like my lithography design for Zeiss, and that is done in the next design.
- 12. f/1.0 and 65 degree field diameter. Diffraction-limited over field at .55u for 25 mm focal length. 4 lenses and 2 mirrors, all aspheric. 2 intermediate images 65 degree field diameter has 24 degree diameter empty area
- 13. Using only part of the 65 degree diameter field system can give an unvignetted f/1.0 field of 10 X 50 degrees or a 20 degrees square field that is diffraction-limited at .55u for 25 mm focal length. For a very narrow line field 60 degrees is possible. With an external pupil scanning is possible. Shows 65 degree image for outer field.
- 14. But to avoid vignetting of rays by the mirrors in this particular design example the inner field diameter must be made a lot larger to get a full 360 degree circle for the image, like this here. But there is no need to do that. The vignetting can be avoiding by only using a piece of the field, as has already been shown.
- 15. External Pupil This shows a typical design’s long direction field of view and the external pupil that could be used for scanning.
- 16. Let us looking at using a flat metasurface to correct the very large amount of color of these fast speed designs. For the 25 mm focal length f/1.0 design the amount of uncorrected color for the .45u to .65u spectral range is almost 200 waves of defocus on-axis and more at the edge of the field, where the polychromatic r.m.s. value is about 95 waves. By adding a flat metasurface to the design both the axial and lateral color can be corrected at the same time if a single metasurface is located at the right place in the design. But the default dispersion of a metasurface (= same as a diffractive surface) results in a large residual amount of higher-order color when this is done. The resulting image still has bad color and very poor image quality. Doing color correction instead by adding lenses of different glass types to the design requires much complexity for a fast speed like f/1.0
- 17. f/1.5, 25 mm focal length, 47 degree field diameter. Here is a color corrected design with a flat metasurface on an extra lens element .45u to .65u color correction Flat metasurface
- 18. f/1.5 design, 25 mm focal length, 45 degree field diameter Color corrected for .45u to .65u with altered metasurface dispersion
- 19. A key feature of this f/1.5 design with excellent color correction is the slightly altered metasurface dispersion. Another important feature that is required for the best performance is that the metasurface provides both power and asphericity. Further work should make the f/1.0 design also have good color correction. The external pupil could be used for scanning and laser scan designs typically have a much slower f# speed and smaller field of view than the designs shown here, because conventional external pupil designs can’t simultaneous have a fast speed and wide field of field with good image quality.
- 20. In summary, the excellent monochromatic image quality of this new type of design can also be given broad spectral band color correction, but good performance requires the use of a flat metasurface with slightly altered dispersion. The default dispersion, however, results in a large amount of residual color and very bad image quality. There is no other way to achieve these really great results in a simple system except by this particular kind of metasurface and that might be used to make a case for metasurface development.