peter.king@LIGO.ORG - posted 07:47, Wednesday 05 October 2016 - last comment - 14:13, Wednesday 05 October 2016(30228)
laser adjustments
The laser power is noticeably lower since the beginning of last week. I increased the diode currents by 0.3A and adjusted the diode temperatures. diode currents were 50.2A, now 50.5A diode box 1: no change diode box 2: reduced temperature from 23 to 21.5 degC diode box 3: reduced temperature from 23 to 22.5 degC diode box 4: no change Laser power went from 158.2W to 166.3W as reported by the power monitor on the MEDM laser screen.
[Jenne, JeffK, Terra, JeffB, Cheryl]
A consequence of this degredation of HPO ouput power is that we have less power incident on the rotation stage's HWP, so the maximum amount of power that we can inject into the vacuum is lower than it has been.
We can and should address this by recalibrating the rotation stage such that we are getting the power we request (after other fixes listed below). But, right now the max power we have available is 48.5W, even if we request more. (Normally one could "cheat" and request some power higher than 50W to get actually 50W, but we can't do that here).
I see 2 possible solutions to this:
I leave it to persons more expert than myself to determine which of these is better. I know that Peter already increased the diode currents this morning (top entry in this thread), so maybe we don't want to do that anymore. But, adjusting the HWP requires a PSL incursion.