Specifications, procurement and testing of the TMT-NFIRAOS double-pyramid prisms
Bibliographic record
Abstract
NFIRAOS, the adaptive optics system of TMT, uses a pyramid wavefront sensor in addition to the 6 LGS WFSs. This pyramid WFS, referred to as Visible NGS WFS (VNW) reach its final design and is now ready for fabrication. One of the high-risk items is the custom achromatic double-pyramid prisms that are very challenging to manufacture. Fortunately, for NFIRAOS we were able to relax the angular tolerance of the pyramid to 2 arcmin. First, this paper lists the main optical specifications and tolerances of the double-pyramid. Then, we present the fabrication process developed by BMV Optical Technologies, our supplier, who successfully produced four double-pyramids. Finally, we describe the sequence of tests we performed at NRC during the incoming inspections; including a new optical test we developed to quickly verify the angular tolerance of the delivered double-pyramid prisms. This is a simple, accurate and robust test that doesn’t require any special lab equipment other than a pinhole source and a stock lens in front of the pyramid, and it is insensitive to lens imperfections and misalignment errors. We call this test the “Metafocus Test” as it makes use of a so-far unknown interesting optical property of the double-pyramid, for which the four exiting beams intercept into a single point. Any angular error on the faces of the pyramid will split the metafocus up to four spots. The as-built apex and azimuth angles, as well as assembly errors (wedge and clocking of front pyramid w.r.t. rear pyramid) can be derived from the measurement of the relative position of each spot.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 0.003 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".