...
- 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.