We have seen slow change in optical gain at the beginning of each lock stretch at LHO. Jenne has a nice alog (LHO alog 22271)  about this varying optical gain.  Here, I am trying to use the calibration parameters kappa_C which is a measure of change in optical gain from its nominal valure of 1. For this analysis, I take the the data that has  Guardian state vector greater than 600 (Low nominal noise) and plot kappa_C from the beginning of each lock stretch to 2 hours into the lock.

The attached plot has total of nine segments starting from Oct 03, 2015. There were total of 12 viable segments but I excluded 3 segments which were more flatter at the beginning. Not sure why these are flatter than the other but excluding those stretches help to visualize the time constant of optical gain better.

The estimated time it takes for the optical gain to reach its nominal values after the IFO is locked is about 30 minutes or so as seen in attached plot.