S. Dwyer, R. Short

During H1's locking troubles this morning, we decided at one point to start an initial alignment from the start since DRMI was not locking. While the ACQUIRE_XARM_IR state was running during the input alignment steps, Sheila noticed the LSC-TR_X signal was far off from zero with no light, meaning there was a dark offset that needed to be fixed. I took the mode cleaner offline so we could observe the dark signal on the POP_A_RF45 photodiode and applied the negative value of that to the offset for both the I and Q segments. This allowed XARM IR to catch quickly, and input alignment completed without issue (contrary to its behavior in recent weeks). Sheila has updated the hard-coded offsets in ALIGN_IFO's PREP_ARM_IR state generator (lines 770-771) and included a note that these need to be updated periodically when input alignment has trouble.

This should fix the troubles we've been seeing with input alignment and serves as a reminder to check for any erroneous changes to dark offsets if we notice issues with alignment steps.