[Daniel, Paul]
We have updated our LHO FINESSE file (https://dcc.ligo.org/LIGO-T1300904) to compute an estimate of the DCCP as requested by Jeff.
The DCCP value we calculated was 369 Hz. This is for a well mode matched and aligned setup.
The optics details were taken from the galaxy page for the various mirrors installed at LHO. We also tried to get some more accurate losses in the arms taken from the following documents:
| Optic | Loss [ppm] | LHO aLOG ref. |
| ITMX | 42 | N.A. |
| ETMX | 78 | 16082 |
| XARM | 120 | 16579 |
| ITMY | 30 | N.A. |
| ETMY | 125 | 15919 |
| YARM | 155 | 15937 |
The caveat here is that the DCCP value has been seen to wander depending on alignment, as was reproduced in some of Gabriele's simulations, https://dcc.ligo.org/LIGO-G1500641. Here Gabriele found a slightly higher well aligned DCCP value of ~380Hz. We know that the DDCP value depends on many variables (alignment, mode mismatch in SRC, arm losses etc.), some of which are not yet well constrained with measurements.
Attached is a plot of the DARM TF from the Finesse model, which is well described by a single pole at 369 Hz.
This is my own reckoning of the loss measurements we've performed after the ETMs were cleaned in December. Note that these visibility measurements do not independently measure losses from the ITMs or the ETMs; they just give the total arm loss from scatter and absorption.
If these measurements are not satisfactory, we could always repeat them.
We could also repeat the ringdown measurements, but we would need to be more careful when collecting the data. Last time, the incident IR power on the arm fluctuated from lock to lock, which made the uncertainties in the inferred losses much too big for the measurements to be usable.
X arm
| Loss | Date | Method | alog | Notes |
| 78(18) | 2015-01-14 | Visibility | 16082 | — |
Y arm
| Loss | Date | Method | alog | Notes |
| 286(33) | 2015-01-05 | Visibility | 15874 | Green WFS not on |
| 125(19) | 2015-01-07 | Visibility | 15919 | — |
| 155(19) | 2015-01-08 | Visibility | 15937 | — |
| 140(16) | 2015-01-09 | Visibility | 15991 | — |