Please ignore the alog above, I will reproduce it here with corrected numbers with the responsivity used correctly. 

Summary: With a cold OM2 we estimate 11% unknown HAM6 losess (including OMC losses, modemismatch, DCPD QE), with hot OM2 that goes to 21%.  We can estimate the change in HAM6 throughput 4 ways, three methods that depend on the DARM offset steps agree that the HAM6 throughput with hot OM2 is 90% of what it is with cold OM2.  The optical gain suggests that the throughput only dropped to 96% of what it was for cold OM2.  

Details:

Last Tuesday we stepped up the ring heater and did a couple of DARM offset steps before and after the change.  The first attachment shows the trends of the two sets of DARM offset steps and the two hour transitent of OM2.  The next plots zoom in on the DARM offset steps, each step was for 1 minute and the steps were larger than in  69653 to help make a small change more easily measureable.  With OM2 cold, the refl diode still doesn't seem like it makes a nice measurement of the darm offset light reflected by the OMC, with OM2 hot it is clear that we can see the change in OMC refl when the DARM offset steps. 

change in HAM6 throughput estimated by AS_C

For both hot and cold OM2, we can use the power change on AS_C to estimate the HAM6 throughput.  Calibrating DCPD sum into Watts using 0.858e-3 A/W gives 86% HAM6 throughput for cold OM2 with 60W input power, and 77% throughput for the hot OM2. This can be compared to 69653, done with 75W input power (430kW in arms) where Jennie W found 82% throughput of HAM6 (Jennie also used 0.858AW for the DCPD responsivity).  We can add up known HAM6 losses from the SQZ loss wiki, 0.993(OM1)*0.985(OM3)*0.9926(OMC QPD) = 97% HAM6 transmission if OMC mode matching, losses and QE were perfect.  This means that we have 11% additional HAM6 losses for a cold OM2, and 21% for the hot OM2.  (The HAM6 throughput with OM2 hot is 90% of what it is with OM2 cold)

change power on AS_C from darm offset and  sidebands/contrast defect

The estimate of the amount of sideband/carrier junk light entering HAM6 based on AS_C is 623mW/624mW with OM2 cold and with OM2 hot it is 634mW.  This 10-11mW increase might be due to the alignment shift in the SRC that Elenna plotted 70886 which could be due to the change in gouy phase on the AS WFS when OM2 changes.  The total power incident on HAM6 increased by 15mW during the OM2 thermal transient, the light from the DARM offset increased by 6-6.6mW.  When the HAM6 throughput changes from cold (eta) to hot (eta') the darm offset has to change from cold X to hot X' = X* sqrt(eta/eta') to keep the power on the DCPDs the same, which increases the DARM offset light on AS_C by eta/eta' (so, as_darm_power_hot/as_darm_power_cold = HAM6 througput cold/ HAM6 throughput cold).  This implies that the HAM6 throughput with OM2 hot is 89% of the HAM6 throughput with a cold OM2.

OMC mode matching from OMC refl diode

The light which is insensitive to DARM in OMC reflection increased from 623.3/624mW to 634.4mW . We can estimate the OMC mode matching with an approach like llo 60885: there is 53mW of darm offset light incident on the OMC for cold OM2 and 59mW for hot OM2 (taking into account known HAM6 losses). We can estimate the mode matching of the OMC (which could include misalignment) as 1-reflected darm offset light/ incident darm offset light which gives 96% mode matching for the cold OM2 (where the measurement may be suspect) and 85.4% or 85.2% mode matching for the hot OM2. This implies that the OMC mode matching with OM2 hot is 89% of what it is with OM2 cold.

Optical gain change

The normalized optical gain (kappa c) dropped from 1 to 0.98 while OM2 was heating up.  Since the power on the DCPDs is kept constant, the DARM offset changes when the HAM6 throughput changes, and the optical gain hot/optical gain cold = sqrt(throughput hot/throughput cold).  Kappa c of 0.98 implies that HAM6 throughput with OM2 hot is 96% of the throughput with OM2 cold.

# DARM offset OM2 scan log file, gps start, gps stop

• 4 1371902418 1371902478
• 10.94319 1371902478 1371902539
• 4 1371902539 1371902599
• 10.94319 1371902599 1371902659
• 4 1371909859 1371909919
• 10.94319 1371909920 1371909980
• 4 1371909980 1371910040
• 10.94319 1371910040 1371910100