| Quote: |
|
| Cavity |
One-way Gouy phase [rad] |
TMS [MHz] |
| PRX |
0.244 |
1.730 |
| PRY |
0.243 |
1.716 |
| SRX |
0.197 |
1.743 |
| SRY |
0.194 |
1.717 |
So, there are regions in parameter space for both options (i.e. keep current G&H mirrors, or order two new sets of folding mirrors) that get us close to the design numbers...
|
Keeping these design numbers in mind, here are a few possible scenarios. The "designed" TMS numbers from my previous elog are above for quick reference.
Case 1: Keep existing G&H mirror, flip it back the right way, and order new PR3/SR3.
- Spec PR3 to be concave with RoC 600 +/- 50m
- This means the TMS in the PRC is in the range 1.4 MHz - 1.6 MHz [see this plot]
- The mode matching efficiency for the PRC is > 98.5% [see this plot]
- The TMS in the SRC is in the range 1.6 MHz - 1.8 MHz [see this plot]
- Mode matching efficiency for SRC is > 98.5% [see this plot]
- PRG between 34-38, depending on uncertainty in measurement of RoC of existing G&H mirror [see Attachment #1, added Nov 11 2016]
Case 2: Order two new sets of folding mirrors
- Spec PR3/SR3 to be flat - for purposes of simulation, let's make it concave with RoC 10 +/- 5 km
- Spec PR2/SR2 to be concave with RoC 1500 +/- 500m
- The TMS in the PRC is between 1.7 MHz and 1.85 MHz [see this plot]
- Mode matching efficiency is >98.5% in the PRC [see this plot]
- TMS in the SRC is between 1.7 MHz and 2 MHz [see this plot]
- Mode matching efficiency >99.0% in the SRC [see this plot]
At first glance, it looks like the tolerances are much larger for Case 2, but we also have to keep in mind that for such large RoCs in the km range, it may be impractical to specify as tight tolerances as in the 100s of metres range. So these are a set of numbers to keep in mind, that we can re-iterate once we hear back from vendors as to what they can do.
For consolidation purposes, here are the aLIGO requirements for the coatings on the RC folding mirrors: PR2, PR3, SR2, SR3 |