After further astigmatism/tolerance analysis [ELOG 15380, 15387] our conclusion is that the stock-optic telescope designs [ELOG 15379] are sufficient for the first round of BHD testing. However, for the final BHD hardware we should still plan to procure the custom-curvature optics [DCC E2000296]. The optimized custom-curvature designs are much more error-tolerant and have high probability of achieving < 2% mode-matching loss. The stock-curvature designs can only guarantee about 95% mode-matching.
Below are the final distances between optics in the relay paths. The base set of distances is taken from the 2020-05-21 layout. To minimize the changes required to the CAD model, I was able to achieve near-maximum mode-matching by moving only one optic in each relay path. In the AS path, AS3 moves inwards (towards the BHDBS) by 1.06 cm. In the LO path, LO4 moves backwards (away from the BHDBS) by 3.90 cm.
AS Path
| Interval |
Distance (m) |
Change (cm) |
| SRMAR-AS1 |
0.7192 |
0 |
| AS1-AS2 |
0.5405 |
0 |
| AS2-AS3 |
0.5955 |
-1.06 |
| AS3-AS4 |
0.7058 |
-1.06 |
| AS4-BHDBS |
0.5922 |
0 |
| BHDBS-OMCIC |
0.1527 |
0 |
LO Path
| Interval |
Distance (m) |
Change (cm) |
| PR2AR-LO1 |
0.4027 |
0 |
| LO1-LO2 |
2.5808 |
0 |
| LO2-LO3 |
1.5870 |
0 |
| LO3-LO4 |
0.3691 |
+3.90 |
| LO4-BHDBS |
0.2573 |
+3.90 |
| BHDBS-OMCIC |
0.1527 |
0 |
|