1. Preliminary Foreoptics Design for FASOT of 2nd Generation L. Chang, X.M Cheng changliang@ynao.ac.cn

2. Outline:  Cassegrain Focus Design  Coude Focus Design

3. 1.Cassegrain Focus Design Telescope Solar image monitor system Polarimeter Image Slicer Optical Design Scheme of 2 nd generation FASOT Design Requirements : Telescope Dia:800mm F/#:f/12 Work Wavelength:400nm-1085nm Sample size (sky):0.5 arcsec FOV:First step is 0.5 arcmin; Final:1 arcmin

4. 1.Cassegrain Focus Design Made By FOV:9 arcmin

5. 1.Cassegrain Focus Design Collimator UV Filter Cal. Wheel FLC1 FLC2 LCVR Polarization Splitter Telescope Focal Plane compensator Image Lens Folding Mirror Image Slicer System IFU and Spectrograph SP Beam PS Beam 2.Ideally, the sky image from the telescope focal plane should be absolutely telecentric over the whole field of view. Modulator 1.Magnify …………

6. 1.Cassegrain Focus Design Advantage of Telecentricity: ** “ The magnified sky image on the microlens surface must be telecentric in order to avoid pupil image shift on the microlens, which may result in light loss that varies across the field. ” ** “ Magnification M is independent of the distance between the object (here it is telescope focal plane) and the foreoptics. Conventional optical systems produce images with higher magnification when the object is closer to the lens. A telecentric system acts as if it has an infinite focal length. An object moved from far away to near the optical system goes into and out of sharp focus,but its image size is constant. ” Deqing Ren and Jeremy Allington-Smith, Publications of the Astronomical Society of the Pacific, 114:866 – 878, 2002 August

7. 1.Cassegrain Focus Design FOV:1 arcmin

8. 1.Cassegrain Focus Design FOV :0.5 arcmin

9. 1.Cassegrain Focus Design Design Result:  Focal length of Collimator:45mm  Image size on telescope focal plane(0.5 arcsec): 23.27um  A Lenslet size:200um  Magnification from telescope focal surface to image slicer/lenslet array:200/23.27=8.594  Focal length of image lens:45*8.594=386.73mm  F/# to Image slicer/Lenslet Surface:12*M=103.12  Fiber array in First Step:30 ” /0.5 ” =60 Fiber numbers:60*60=3,600 for SP Beam or PS Beam,Total:7,200  Final Step:60 ” /0.5=120 Fiber numbers:120*120=14,400 for SP Beam or PS Beam,Total:28,800 for 4 image slicers, each one for 3,600 fibers for SP Beam or PS Beam

10. 1.Cassegrain Focus Design Design Result:  Fiber Core Dia: 60um  F/# to fiber: f/7  Lenslet focal length:1400um  Pupil image on fibre core: 1400/(103.12*1.51) =8.95um  F/# of fiber output: 1/ (2*(1/7)^2)^(1/2)=f/4.95 f/103.12 f/7

11. 1.Cassegrain Focus Design Maximal area error :4.84% Minimum area error: 0.1% o Spot Diagram

12. 1.Cassegrain Focus Design

13. Equatorial mounting

14. 2. Coude Focus Design Rotator: K mirror Right Ascension axis Declination axis Optical Bench Equatorial mounting Polarimeter

15. Discussion 1.Cassegrain Focus: fiber system following telescope to move,fiber may be pulled, twistied …… may be Broken 2. Coude Focus Design ： **Optical Path is 4470mm,alignment is difficult **Rotator precision must be higher SP and PS Beam coupled to lens array must be co-spatially aligned or registered.

16. The End Thanks