Pcal Team,
The displacement calibration factor that converts the TxPD (photodiode that measures a small amount of sampled light going to the ETM) and RxPD (photodiode that measures all of the reflected light from the ETM) readings into metres are now reported in DCC document # T1500252.
We have calibrated photon calibrator at each end-stations (both LHO and LLO) multiple times after installation. This document contains all the calibration factors obtained on different dates. However, the numbers obtained at different dates for each endstation are within a percent of each other when they were measured under "identical conditions". There has been some optical layout changes in the Transmitter module (described in LHO alog #17145 ) which has resulted in different displacement calibration factor for TxPD over time as you will notice in the table in DCC document linked above. But these numbers are consistent with the changes that were made.
For RxPD, the calibration factor at LHO has been measured consistently within 1% percent. However, we noticed recently that LLO had their calibration factor differ from LHO by about 20%, although the calibration numbers from different dates for same end-station agreed within a percent. We were not sure about why the sensitivity of these detector were different despite the components being same. This should not effect the calibration but we nonetheless replaced those two RxPD at LLO with two spare RxPD and now the calibration numbers at LLO are comparable with LHO. So the latest calibration number for RxPD from LLO is about 20% more than what it usually has been.
Recently, we noticed some power variation in the RxPD signal (while TxPD stays flat) and also variation in optical efficiency. We are actively looking into this issue and have some leads. We will put an alog about it soon. However, this should not alter the calibration factor by more than a few percent at its max.