Open Access
Table 4
As-built transmission budget.
| Component | 1500 nm | 1600nm | 1700nm | Description |
|---|---|---|---|---|
| Sky | 91% | 96% | 98% | From ESO SkyCalc |
| Telescope | 80% | 80% | 80% | 3 reflective surfaces + dust on primary mirror |
| SPHERE CPI | 55% | 57% | 46% | SPHERE commissioning measurements |
| FIM | 87% | 88% | 90% | 2 reflective + 4 transmissive optics, as-built AR coatings |
| Strehl | 83% | 85% | 86% | Bright guide star (R = 3), median conditions, SPHERE NCPA |
| Pointing error | 88% | 89% | 90% | 8 mas pointing error (El Morsy et al. 2022) |
| Coupling efficiency | 76% | 76% | 76% | VLT pupil |
| Fiber transmission | 96% | 95% | 94% | Fiber absorption, as-built AR coatings |
| FEM | 91% | 92% | 93% | 1 reflective + 3 transmissive optics, as-built AR coatings |
| CRIRES | 16% | 19% | 19% | AIT laboratory measurements |
| Total | 2.7% | 3.7% | 3.1% | |
| Measured on sky | 2.2% | 3.3% | 3.1% | HIP 108085, 0.7–0.8″ seeing, clear sky conditions |
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