Page Comparison

Note: discussion of some of this hardware and different options is also here: https://confluence.lsstcorp.org/display/LTS/Readout+and+Timing+Options+for+CBP+Calibration

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Powerpoint with initial version of hardware design: CBP_large_lens_calibration_system.pptx

Updated version: CBP_large_lens_calibration_system_v2_060923.pptx

lens: https://www.ebay.com/itm/184986621155?chn=ps&_trkparms=ispr%3D1&amdata=enc%3A1G08XAgSuSmibxPFCG1ZFlQ82&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=184986621155&targetid=1587268788377&device=c&mktype=pla&googleloc=9002000&poi=&campaignid=19894961968&mkgroupid=148855406073&rlsatarget=pla-1587268788377&abcId=9307911&merchantid=113505756&gclid=CjwKCAjw-IWkBhBTEiwA2exyO38BmKS59kDX7yC1bDVaryyAKyGwXfi_9vPYCjG1mPkSEO2YcfymaxoCHIoQAvD_BwE

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• biggest concern for whether the spot fits on the photodiode is chromatic aberration for a spherical lens
• build access panel/hatch instead of having a tube connector
• lens covers should be metal and they should be actuated
• whole assembly should go on the TMA, either at the top of they pylons or by the primary mirror
• should use black rubber coverings or honeycomb aluminum instead of sheet metal rings
• need to design an adapter from cylinder to rail for the lens holder (cylindrical to rectangular)
• consider using 3-4 aluminum rings to stabilize the tube
• for mounting the lens
  • use 3 100 mil teflon pads as inserts
  • at same location drill 1/4" through holes in radial direction
  • squeeze RTV through those holes
  • use CTE of glass, RTV, and aluminum to determine the appropriate size of the gap to make everything athermal
  • machine aluminum clips to dimension of known gap from CTV calculation
• For the logic timer - if we need to switch out the Keithley 6514 for the 6517B we can
  • check timings - see if that's a viable option
  • could make new CSC if necessary - figure out if it is

Measurements of beam spot size 

Tried to measure beam spot size through the two 300 mm lenses on 9/7/2023.

Setup: Collimated an LED with one 300 mm lens and then focused it with another. Used a red LED to perform these measurements. (First I used a broadband LED but there's obvious chromatic aberration when you do that).

General observations: spherical aberration seems larger than expected, but it is much worse when the flat side of the lens faces the collimated beam. Qualitatively that is what we expect (see e.g.  https://www.comaroptics.com/technical/spherical-aberration). However, doing calculations based on the link page implies that spherical aberration should make the beam on the order of 1mm in size, but it didn't quite fit in the standard NIST hamamatsu photodiode (it almost did, but not quite).

But doing a simple sum over the whole spot taken with the canon camera, the total flux from the spot is identical to far less than a percent (or even one part per thousand) CBP_calibration_spot_flux.ipynb. This is extraordinarily weird to me because the glass should reflect 4% of the light.

For an estimate of spot size (very, very crude - based on the above notebook, but I apparently failed at focusing even just on the fiber so take this with a grain of salt): spot size = 40 pixels (by eye this is an overestimate) * 5.25 um = 210 um. With an 800 mm lens that corresponds to an angle of .21/800 = .26 mrads. If we're 3 or 4 meters away that's (say 4): ~1mm. Huh. That is definitely not what I observed as a spot size...  

Things built in shop:

Version for photodiode holder: 9/27/2023 Photodiode_holder_design.pptx

9/27/2023 sent this to shop: pinhole_holder_2 v6.step

Items that have been built in the shop: Rail_Connector.step Tube_End.step Tube_End_Drawing.pdf Rail_connector_drawing v3.pdf CBP_Calibration_Tube_end_drawing v3.pdf

New tube end design

Updating the tube end design so that we can mount a breadboard on it. I also increased the size of the center hole to 3", since we will be putting more cables through it.

tube end with board v2.step

Parts for baffling and possibly a flip mirror? There are a bunch of possible options:

1. If we just use a Hamamatsu NIST photodiode then we can use the current tube end and use an SM2 tube to anchor it there and an SM1 (with adapter) to mount the photodiode. This is easiest. We can also attach another 2" tube and add baffling.
2. If we add in a flipper mount to image on a camera, we want right angle brackets to be able to mount the flipper and camera.
3. If we want to use a Fabry Lens (which may not work due to issues with chromatic aberration), then we need a cage system to set up the alignment.