preliminary foreoptics design for fasot of 2nd generation l. chang, x.m cheng [email protected]
TRANSCRIPT
Outline:
Cassegrain Focus Design
Coude Focus Design
1. Cassegrain Focus Design
Telescope
Solar image monitor system
Polarimeter
Image Slicer
Optical Design Scheme of 2nd generation FASOT
Design Requirements:Telescope Dia:800mmF/#:f/12Work Wavelength:400nm-1085nmSample size (sky):0.5 arcsecFOV:First step is 0.5 arcmin; Final:1 arcmin
1. Cassegrain Focus Design
Made By
FOV:9 arcmin
1. Cassegrain Focus Design
Collimator
UV Filter Cal. Wheel
FLC1
FLC2
LCVRPolarization Splitter
Telescope
Focal Plane
compensator
Image Lens
Folding Mirror
Image Slicer System
Image Slicer System
IFU and Spectrograph
SP Beam
PS Beam
2.Ideally, the sky image from the telescope focal plane shouldbe absolutely telecentric over the whole field of view.
Modulator
1.Magnify…………
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 theobject 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
1. Cassegrain Focus Design
FOV:1 arcmin
1. Cassegrain Focus Design
FOV :0.5 arcmin
1. Cassegrain Focus Design
Design Result:Focal length of Collimator:45mmImage size on telescope focal plane(0.5 arcsec): 23.27umA Lenslet size:200umMagnification from telescope focal surface
to image slicer/lenslet array:200/23.27=8.594Focal length of image lens:45*8.594=386.73mmF/# to Image slicer/Lenslet Surface:12*M=103.12Fiber array in First Step:30”/0.5”=60
Fiber numbers:60*60=3,600 for SP Beam or PS Beam,Total:7,200Final 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
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/103.12f/7
1. Cassegrain Focus Design
Maximal area error :4.84%
Minimum area error: 0.1%o
Spot Diagram
1. Cassegrain Focus Design
1. Cassegrain Focus Design
Equatorial mounting
2. Coude Focus Design
Rotator: K mirror
Right Ascension axis
Declination axis
Optical Bench
Equatorial mounting
Polarimeter
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 higherSP and PS Beam coupled to lens array must be co-spatially aligned or registered.
The End
Thanks