TMS Meeting Minutes, October 22, 2020

Attendees: Andrew, Breann, Heejoo, John, Trenton, Yang (Zoom Meeting)

Meeting Notes:

  • Updates on the trip up the mountain
  • Christian hasn't responded, looks like we'll be unable to be in-person at LBT for a while (COVID)

  • Andrew suggests we need to put this into a document with action items and the necessary steps to install TMS on Sx side
  • We need to tell Christian what we need to do and why
  • Reasonably urgently, we need to install a binocular TMS for the LBCr + LBCb
  • Need a schedule, white document, with our needs and puts action items into motion with

  • At the end of the day, Christian is going to make a management decision, but we can provide him with a reason to support our cause
  • If we can show some positive results on the Dx side, we may be able to have our action items put in place sooner
  • Andrew doesn't think we should make a resource request from Christian contingent upon our success on the Dx side
  • John suggests we should move to just ask Christian if we can just go ahead and install on Sx

  • Today, Ch. 11 alignment was reacquired, thanks to Leroy and John
  • However, we have to use the max gain to get 20% return from Ch. 11
  • Last night's data had Ch. 17 acting up
  • Andrew would like Ch. 17 to be looked at, as well
  • Heejoo mentioned that there is need for cleaning the fiber tips, especially for channels 11/17
  • To Andrew's mind, it is a fairly binodal situation; when there is poor return, the channels essentially just drop
  • When the telescope moves, the beam footprint from the retro walks off the collimator, effectively demanding an increase in the NA of the fiber collimator
  • We are really measuring contrast on the fiber (reminder)
  • All channels currently looking at LBC right now are using the large collimators

  • Etalon spent time adjusting the tuning of the fiber collimators to get the maximal signal measurement on the contrast
  • Want big offsets (deliberately defocus the beam) the beam to spread out the energy on the retro

  • Andrew's updates on the solid Maksutov retro (like a Reed pupil relay + an Offner image relay)
  • Utilizes 30% BS on the buried surface to bounce light back out after inducing SA on the way in and removing on the way out
  • Beam retraces right on top of it's input
  • Also behaves like an solid Offner relay; able to use this to test the optical system
  • Able to get a null test using this system in the Offner configuration
  • This system actually flips the beam about the center of the aperture

  • Yang on ch. dropping handling
  • Working on it, would like to schedule a test in the later part of next week
  • If not possible, early part of the following week (end of Oct., start of Nov.)
  • Yang thinks he should have a test version relatively quickly
  • Andrew reminds us that last night's data has Ch. 17 dropping in and out throughout the night, and would like Yang to test his code with this data
  • Yang's understanding is that whenever a channel or multiple channels are dropped, a correction vector is to be applied
  • Can't say that he has 100% certainty about how the correction vector is designed
  • For some cases, we don't have to make any correction vector at all; could go back and make a reconstruction vector

  • Based on the mathematical file, correction vector def. as:
  • Whenever you have a dropped channel, compute pose changes with a vector using the correction to the dropped channel (from the last set of data) and subtract this from the pose change w/o the dropped channel included
  • Reconfigured matrix with last channel measurement (or reference vector, Yang's suggestion) applied to dropped channel
  • Difference between 9 ch. pose with substituted correction vector and 8 ch. pose w/o dropped channel used as actual pose
  • Andrew suggests that there is a difference between using the reference vector for correction and the last measured channel vector, and that it would be preferrable to use the last measured channel vector for correction
  • Andrew requests that, if we get test time, we also drive in astigmatism to work on fitting to mirror shape

  • John confirms that astigmatism was driven on the mirror today
  • +/- 5000 astig, and also spherical
  • Predicted change in Z, and a total change in length observed
  • Can also see predicted change in diameter
  • The measurement of the terms is in RMS
  • So 5000 astig corresponds to 5 microns

  • Plan is for Heejoo to schedule a test for about a week from now
  • Yang's question:
  • Suppose we never get a full 9 ch. measurement for an entire night
  • Do we still need to apply a correction?
  • Most of the time we have an 8 ch. and then we'll drop to 7 or 6 ch.
  • If able to get full 9 ch. vector, there are some combinations of possibilities
  • Use whatever the last working meas. was
  • What about if we are working with 7 channels and then we get a different set of 7 channels
  • Consider either skipping the measurement or configuring for a different set of the 7 channel
  • Good practice to work through all of the contingencies
  • Yang hoping for the software to work for all possible cases
  • Yang and Andrew to discuss this together to develop a procedural algorithm for testing the channel dropping handling

  • Trent will be presenting on TMS at Industrial Affiliates Poster Session next week

  • Andrew would like to attend the next test (prefers Tucson afternoon)
  • Handover of telescopes is about 3:40 PM, about 2 hours before sunset
  • Heejoo suggests 1:00 PM ish for doing a test, and he prefers Tuesday (could be Friday)
  • Andrew happy to report that we are developing algorithms for channel dropping, and we want good results
  • Want to be able to say that it's working, at least a good prototype
  • For SPIE papers, good to talk about the various failures and problems
  • Yang will make an effort to give a summary of what the algorithm is doing for Andrew's paper

-- TrentonBrendel - 23 Oct 2020
Topic revision: r1 - 23 Oct 2020, TrentonBrendel
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