Kiwamu, Lisa


There has been some confusion about the power we were measuring in the REFL path, compared to the expected one. Most of the confusion was due to a BS in the in air path which was forgotten to be taken into account, and the assumption of getting 10 W back from PRM, while it is significantly less than that. The previous entry was right in the final message, but a couple of things were wrong...so I post another summary here.

Pin = 8.8 W entering the IMC, measured on the PSL table;
I checked with Paul and Giacomo that a good number for the transmission PSL - IMC - PRM back to the Faraday is something like 83%, so I will use T = 80% as a round number for the transmission from the PSL back to HAM1 the PRM is aligned; 
given the HAM1 path, we expect 1.25% of the REFL power which arrives on HAM1 to reach the LSC RF diode P_exp = 8.8 * 0.8 * 1.25e-2 = 88 mW;
in counts, this means: 88e-3 [W] x 0.76 [A/W] x 200 [Ohm] x 1638 [counts/V] = 21900 counts; 
Measurement: LSC IN VAC REFL A (LSC RF PD) (1.25% of REFL power) = 15900 counts (maximum found by moving RM2) 
    This corresponds to 64 mW, by using signal chain calibration;
Measurement: LSC REFL AIR A (LSC RF PD) (0.625% of REFL power) = 7955 counts
    32.5 mW measured directly in front of the diode on table (30.4 mW using signal chain calibration)
Measurement: LSC REFL AIR B (BBPD) (0.625% of REFL power) = 21770 counts
    34 mW measured directly in front of the diode on table

 Conclusions 
 From the in air LSC REFL A diode we see that the signal chain calibration agrees with the direct measurement of the power; 
 The total amount of light in the in AIR REFL path is 66.5 mW, which is the same power we see on the in vac diode, as expected; 
 The absolute value of the power we see is 25% - 30% less than what we expect, but we don't know exactly how much light makes it through the Faraday, and we don't have a direct measurement of the 1.25% transmission through the HAM1 optics, so this doesn't seem a big deal; 
 Based on these numbers, we don't think we have a problem. 

P.S: Still need to calibrate these numbers for the WFSs, measurements were taken all at the same time. 

WFS in vac REFL A (0.625% of REFL power) = 34200 counts
WFS in vac REFL B (0.625% of REFL power) = 36400 counts