Offner imaging system with reduced-diameter reflectors

1. A projection optical system for digital lithography, the system comprising:

an Offner imaging system defining an optical axis and having a well-corrected region; and

means for shaping an optical beam having an extent too large to fit within the well-corrected region to propagate through the Offner imaging system within the well-corrected region.

2. The projection optical system of claim 1 , in which the means for shaping comprises means for reducing a dimension of the optical beam.

3. The projection optical system of claim 2 , in which the means for reducing comprises a mirror system concentric with the optical axis, in which the mirror system directs the optical beam through the well-corrected region.

4. The projection optical system of claim 3 , in which the mirror system comprises:

a frustoconical internal reflective surface facing the optical axis, concentric with the optical axis, and further from the optical axis than the well-corrected region; and

a frustoconical external reflective surface facing away from the optical axis and concentric with the optical axis, the frustoconical external reflective surface aligned to direct light reflected by the frustoconical internal reflective surface through the well-corrected region.

5. The projection optical system of claim 4 , in which the mirror system further comprises a semi-frustoconical internal reflective surface aligned with the frustoconical internal reflective surface and operable to focus the output optical beam in an image plane of the projection optical system.

6. The projection optical system of claim 1 , in which:

the optical beam is a partially coherent; and

the means for shaping comprises means for segmenting the optical beam into segments and for directing the segments into the well-corrected region.

7. The projection optical system of claim 6 , in which the optical beam is non-coherent.

8. The projection optical system of claim 6 , in which the means for segmenting comprises mirror segments aligned to direct the optical beam through the well-corrected region.

9. The projection optical system of claim 8 , in which the mirror segments comprise:

a turning mirror; and

a pair of folding mirrors aligned with the turning mirror and the well-corrected region, in which the pair of folding mirrors is positioned in a plane perpendicular to the optical axis and offset along the optical axis from the well-corrected region.

10. The projection optical system of claim 8 , in which:

the mirror segments comprise:

first folding mirrors aligned with the well-corrected region, and

second folding mirrors each aligned with the well-corrected region and with a respective one of first folding mirrors; and

the first folding mirrors and the second folding mirrors are located in a plane perpendicular to and circumferentially aligned about the optical axis and offset along the optical axis from the well-corrected region.

11. A method of imaging a spatial light modulator, the method comprising:

providing an Offner imaging system defining an optical axis and having a well-corrected region;

emitting an optical beam from the spatial light modulator, the optical beam having an extent too large to fit within the well-corrected region; and

shaping the optical beam to propagate through the Offner imaging system within the well-corrected region.

12. The method of claim 11 ,in which the shaping comprises:

reducing a dimension of the optical beam.

13. The method of claim ii, in which:

the emitting comprises emitting the optical beam as a partially-coherent optical beam; and

the shaping comprises segmenting the optical beam into segments, and

directing the segments of the optical beam through the well-corrected region.

14. The method of claim 11 , additionally comprising:

directing the optical beam through the well-corrected region to provide an output optical beam; and

imaging the output optical beam.

15. The method of claim 14 , in which the imaging comprises focusing the output optical beam.

16. A projection optical system for digital lithography, the system comprising:

an Offner imaging system defining an optical axis and having a well-corrected region; and

a mirror system, concentric with the optical axis, operable to shape an optical beam having an extent too large to fit within the well-corrected region to propagate through the Offner imaging system within the well-corrected region.

17. The projection optical system of claim 16 , in which the mirror system comprises:

a frustoconical external reflective surface facing away from the optical axis, concentric with the optical axis and aligned to the well-corrected region; and

a frustoconical internal reflector surface, facing the optical axis, concentric with the optical axis and further from the optical axis than the frustoconical external reflective surface, the frustoconical internal reflector surface operable to reduce a dimension of the optical beam and to direct the reduced-dimension optical beam towards the frustoconical external reflective surface.

18. The projection optical system of claim 16 , in which the mirror system further comprises a semi-frustoconical internal reflector surface aligned to the frustoconical internal reflector surface and operable to focus the optical beam in an image plane.

19. The projection optical system of claim 16 , in which:

the optical beam is partially coherent;

the mirror system comprises:

a turning mirror located to accept a segment of the optical beam, and

a pair of folding mirrors aligned with the turning mirror and the well-corrected region; and

the turning mirror and the pair of folding mirrors form an image of the segment at an image plane.

20. The projection optical system of claim 19 , in which the optical beam is non-coherent.

21. The projection optical system of claim 16 , in which:

the optical beam is partially coherent, and

the mirror system comprises:

first folding mirrors aligned with the well-corrected region, in which the first folding mirrors segment the optical beam into segments, and

second folding mirrors aligned with the well-corrected region and each aligned with a respective one of the first folding mirrors, in which the segments propagate through the Offner imaging system in the well-corrected region to form images of the segments in a reverse order at an image plane.