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ao:lab_ao [2018/07/06 13:37]
127.0.0.1 external edit 		ao:lab_ao [2018/07/07 09:49]
jones
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- The Lab AO system has to roughly conjugate the pupil onto a deformable mirror. In order to see where the "pupil" is, the following diagram is useful:\\ \\ {{/file/view/PATH-1.jpg/478635094/800x374/PATH-1.jpg|PATH-1.jpg}}\\ \\  The shortest and longest distances are not realistic. e.g. W2 is essentially never used with the long POPs. A 200m distance is roughly the minimum realistic total distance from telescope to BRT primary.\\ \\  The focal lengths of the CHARA BRT are:\\ +====== Lab AO ====== 
 + The Lab AO system has to roughly conjugate the pupil onto a deformable mirror. In order to see where the "pupil" is, the following diagram is useful:\\ \\ {{ao:PATH-1.jpg|PATH-1.jpg}}\\ \\  The shortest and longest distances are not realistic. e.g. W2 is essentially never used with the long POPs. A 200m distance is roughly the minimum realistic total distance from telescope to BRT primary.\\ \\  The focal lengths of the CHARA BRT are:\\ 
  
   - BRT Primary: 1280mm   - BRT Primary: 1280mm
   - BRT Secondary: -192mm   - BRT Secondary: -192mm
-\\  If the BRT secondary is translated, then the beam can come to a focus, and after the focus the beam strikes in order a DM, a collimating spherical mirror, a dichroic and the LDC. The LDC shouldn't be in a converging or diverging beam. Aberrations are minimised by the BRT secondary being translated at the same time as being refocused.\\ \\  The total space from the BRT secondary to the DM is limited to somewhere in the range 2.3 to 2.45m, depending on which email from Laszlo I use. One diagram from Laszlo is below, which indicates that 1280mm + 200mm + 820mm + 150mm = 2.45m.\\ {{/file/view/CHARA_mech.png/478644254/648x486/CHARA_mech.png|CHARA_mech.png}}\\  Working with 2.3m space and a 200m conjugation, we get the following numbers:\\ +\\  If the BRT secondary is translated, then the beam can come to a focus, and after the focus the beam strikes in order a DM, a collimating spherical mirror, a dichroic and the LDC. The LDC shouldn't be in a converging or diverging beam. Aberrations are minimised by the BRT secondary being translated at the same time as being refocused.\\ \\  The total space from the BRT secondary to the DM is limited to somewhere in the range 2.3 to 2.45m, depending on which email from Laszlo I use. One diagram from Laszlo is below, which indicates that 1280mm + 200mm + 820mm + 150mm = 2.45m.\\ {{ao:CHARA_mech.png|CHARA_mech.png}}\\  Working with 2.3m space and a 200m conjugation, we get the following numbers:\\ 
  
   * BRT secondary moves towards primary by 22.9mm   * BRT secondary moves towards primary by 22.9mm
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   * After e.g. 300mm, the beam hits the dichroic.   * After e.g. 300mm, the beam hits the dichroic.
   * After e.g. 300mm, the beam hits the LDC   * After e.g. 300mm, the beam hits the LDC
-The thin-lens formula simple script that Mike used to make these calculations is [[/file/view/chara_ao_calcs.py/478648308/chara_ao_calcs.py|{{http://www.wikispaces.com/i/mime/32/empty.png?32x32|chara_ao_calcs.py}}]][[/file/view/chara_ao_calcs.py/478648308/chara_ao_calcs.py|chara_ao_calcs.py]]\\  +The thin-lens formula simple python script that Mike used to make these calculations is  
- +  import numpy as np 
-  * [[/file/detail/chara_ao_calcs.py|Details]] +  import matplotlib.pyplot as plt 
-  * [[/file/view/chara_ao_calcs.py/478648308/chara_ao_calcs.py|Download]] +   
-  * 1 KB +  f1 = 1280. 
-.\\ \\  The wavefront sensor could be built around the 18-00079 microlens array from SUSS - 53 Euro each. These have a 30 micron pitch, meaning that with a 5 lenslet sampling across the pupil (19 lenslets altogether), the desired pupil size is 0.15mm. If there aren't enough of these in stock (SUSS are now listing these as a discontinued product), a microlens array with a different geometry may be needed. It is critical to have no more than about (focal length) * lambda * 20 > pitch^2, in order to not take up too many pixels. So an alternative is [[http://www.suss-microoptics.com/shop/microlens-arrays/fused-silica/square-lenses/microlens-array-nr-18-00216.html|18-00216]]. The catch is that this is a 10mm x 10mm piece, which ideally we'd want to be diced up.\\ \\  The key is that with 3 lenses plus the microlens array, there isn't that much sensitivity loss (it is a slow wavefront sensor) and with catalog parts we can be flexible.\\ \\  After the beamsplitter, towards the wavefront sensor, we need for the 30 micron pitch version:\\ +  f2 = 192. 
 +  dz = 22.9#15 + np.arange(200)/10. 
 +  sep = f1 - f2 + dz 
 +  smallpsize=19.0 
 +  # focus_from_secondary 
 +  ffs = 1.0/(1.0/(f2-dz) - 1.0/f2) 
 +  #pupil distance (in mm) 
 +  pd = 200000. 
 +  #pupil distance to secondary 
 +  pds =  1.0/(1.0/f1 - 1.0/pd) - (f1 - f2 + dz) 
 +  #pupil image from secondary: 
 +  pfs = 1/(1/pds - 1/f2) 
 +  psize = smallpsize*(f2-dz)/f2*(pfs-ffs)/ffs 
 +  #19mm collimator from pupil 
 +  frat = ffs/(smallpsize*(f2-dz)/f2) 
 +  colfs = ffs + smallpsize*frat 
 +  colfdm = colfs - pfs 
 +  #plt.plot(pfs,psize) 
 +\\  The wavefront sensor could be built around the 18-00079 microlens array from SUSS - 53 Euro each. These have a 30 micron pitch, meaning that with a 5 lenslet sampling across the pupil (19 lenslets altogether), the desired pupil size is 0.15mm. If there aren't enough of these in stock (SUSS are now listing these as a discontinued product), a microlens array with a different geometry may be needed. It is critical to have no more than about (focal length) * lambda * 20 > pitch^2, in order to not take up too many pixels. So an alternative is [[http://www.suss-microoptics.com/shop/microlens-arrays/fused-silica/square-lenses/microlens-array-nr-18-00216.html|18-00216]]. The catch is that this is a 10mm x 10mm piece, which ideally we'd want to be diced up.\\ \\  The key is that with 3 lenses plus the microlens array, there isn't that much sensitivity loss (it is a slow wavefront sensor) and with catalog parts we can be flexible.\\ \\  After the beamsplitter, towards the wavefront sensor, we need for the 30 micron pitch version:\\ 
  
   * A 25mm diameter, 150mm focal-length achromat that forms a new pupil image.   * A 25mm diameter, 150mm focal-length achromat that forms a new pupil image.
ao/lab_ao.txt · Last modified: 2018/07/07 10:08 by jones

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