This morning we continued to use the crane that Camilla and Ryan devised to try to get more reliable power budgeting measurements on the VIP.  Our previous measurements with the power meter held in a hand and hovering over the table consistently showed that we have something like 4% extra losses in HAM7, but they have not been repeatable enough for us to track down the location of the losses.  The crane set up helps us set the angle of the beam profiler head by using a clamp on the post, and also gives us much more steady measurements of power, so we were able to make some progress in identifying the location of losses.  However, we think that the power out of the OPO was drifting by 1-2% during these measurements, which makes the measurements less reliable for finding losses.  

We do think that we have about 0..8% loss at B:L2, where the difficult to align apperture stop is.  This apperture stop catches a rejected beam from B:P1 which is scattered light from the interferometer, so we need to keep it.  We looked for space to move it off the lens mount onto it's own separate mount, but the platform is very crowded with bases and dog clamps in this area, so that would not be an easy solution.  

For the naming of optics see:  D2000021

• (location A) after SFI1 return (before BM1): 1.251mW. (readjusted crane and centering of beam on power meter)
• (same location as A) Moving FC1 and watching SFI1 Return power. Starting P 225, Y -156 (We do not see obvious evidence of clipping in SFI1 on the return path in this data).  
  • 205 Pitch  1.247mW, STD dev 0.59uW
  • 225urad Pitch   1.247mW, STD dev 0.51uW
  • 245urad Pitch   1.247mW, STD dev 0.88uW
  • -156urad Yaw 1.246mW, STD 0.66uW
  • -136urad Yaw 1.246mW, STD 0.57uW
  • -176urad Yaw 1.243mW, STD 0.54uW
  • Starting 1.246mW, STD 0.5uW
• (location B) between SFI1 polarizer and rotator (on way to FC): mean 1.315mW std: 0.41uW.  Comparing this to above numbers it implies we have a loss of 4.9%, 5.2%, or 3.4% using number below, where we expect 2%
  • We decided to measure here instead of right out of the OPO because we were concerned that the slight angle of the beam coming out of the OPO might have been making it hard for us to put the power meter head perpendicular to the beam, and it was easier to get the angle right in this location.  In the end we got similar powers and loss estimates measuring here as measuring right out of the OPO.
• (same location as A) after A:P1 : 1.269mW STD dev 1.4uW; unlocked reloacked OPO retook to be 1.270mW STDdev 2.3uW;  1.270mW STDdev 1.7uW. Implies loss of 3.5% where we expect 2%
• (location C) after B:L1: 1.260mW std 2.1uW  1.259mW std 1.5uW 1.258mW 1.8uW 1.260mW 1.2uW Implies 0.8% loss from B:L2, probably clipping on apperture stop.
• (repeat of location B) back to between SFI1 polarizer and rotator (on way to FC) 1.330mW std 0.66uW 1.329mW std 0.67uW 1.329mW std 0.46uW  Power must have drifted up 1% since our first measurement here.
• after SFI1 before A:L2 : 1.327mW std 0.91uW  1.328mW .66uW 1.326mW 0.80uW 1.324mW std 1.1uW This implies very low loss from SFI1's rotator and 2nd polarizer, although it is possible that the rejected beam from A:P2 could also be on the power meter in this location, we could not identify that beam on a card. If the apparent loss of about 1% from each pass of SFI1 is really from misrotation the rejected beams would contain about 10uW, which we could search for more thourughly with the lights off using an IR card with a viewer.  
• after A:M3 1.321mW std 0.37uW; 1.321mW std 0.52uW; 1.320mW std 0.6uW; 1.320mW std  0.5uW Implies 0.5% loss probably at the aperture stop attached to A:L2.  
• back to after SFI1 before A:L2: 1.305 std 0.7 1.305 mW std 0.7uW 1.316mW Power is drifting enough to make these measurements confusing.