Calcite Brewster PBS Continued

The transmission loss of the Calcite brewster PBS (eLIGO squeezer OFI) was measured with different conditions.
The measured loss was 3600+/-200ppm. (i.e. 900+/-50 ppm per surface)
The measurement error was limited by the systematic error, probably due to the dependence of the PD response on the spot position.

I wonder if it is better to attenuate the beam by a ND filter instead of HWP+PBS.

o First PBS power adjustment -> full power transmission, OD1.0 ATTN Full Power
   PDA20CS Gain 10dB
   Thru 0.746711, PBS 0.744155 => Loss L = 3423 +/- 5ppm

o Same as above, PDA20CS Gain 0dB (smaller amplitude = slew rate less effective?)
   Thru 0.748721, PBS 0.746220 => L = 3340 +/- 5ppm

o Same as above but OD1.4 ATTN
   Thru 0.744853, PBS 0.742111 => L = 3681 +/- 5ppm

o More alignment, more statistics
(PDA20CS 0dB gain =  0.6A/W, 1.51kV/A)
PD(REF, 0dB) 0.426V = 0.47W
PD(MEAS, 0dB) Thru 0.320V, PBS 0.318V = 0.35W, L = 6000+/-3000ppm

Chopping 234Hz, TF 1.6kHz AVG10
Thru 0.745152, PBS 0.742474 => 3594 +/- 5 ppm
Thru 0.745141, PBS 0.742467 => 3589 +/- 5ppm
Thru 0.745150, PBS 0.742459 => 3611 +/- 5ppm
Thru 0.745120, PBS 0.742452 => 3581 +/- 5ppm
Thru 0.745153, PBS 0.742438 => 3644 +/- 5ppm
=> 3604ppm +/-25ppm

o More power

Attenuation OD 1.0
PD(REF, 0dB) 0.875V = 0.97W
PD(MEAS, 0dB) Thru 0.651V, PBS 0.649V = 0.72W, L = 3100+/-1600ppm

Chopping 234Hz, TF 1.6kHz AVG10
Thru 0.746689, PBS 0.743789 => 3884 +/- 5ppm
Thru 0.746660, PBS 0.743724 => 3932 +/- 5ppm
Thru 0.746689, PBS 0.743786 => 3888 +/- 5ppm
Thru 0.746663, PBS 0.743780 => 3861 +/- 5ppm
Thru 0.746684, PBS 0.743783 => 3885 +/- 5ppm
=> 3890ppm +/- 26ppm

o Much less power

Attenuation OD 2.4
PD(REF, 0dB) 67.1mV = 74.0mW
PD(MEAS, 0dB) Thru 53.7V, PBS 53.5V = 59mW, L = 3700+/-1900ppm

Thru 0.745142, PBS 0.742430 => 3640 +/- 5ppm
Thru 0.745011, PBS 0.742557 => 3294 +/- 5ppm
Thru 0.744992, PBS 0.742537 => 3295 +/- 5ppm
Thru 0.745052, PBS 0.742602 => 3288 +/- 5ppm
Thru 0.745089, PBS 0.742602 => 3338 +/- 5ppm
=> 3371ppm +/- 151ppm

o Much less power, but different gain

Attenuation OD 2.4
PD(REF, 20dB) 662mV = 73.1mW
PD(MEAS, 20dB) Thru 501V, PBS 500V = 55.3mW, L = 2000+/-2000ppm

Thru 0.744343, PBS 0.741753 => 3480 +/- 5ppm
Thru 0.744304, PBS 0.741739 => 3446 +/- 5ppm
Thru 0.744358, PBS 0.741713 => 3553 +/- 5ppm
Thru 0.744341, PBS 0.741719 => 3523 +/- 5ppm
Thru 0.744339, PBS 0.741666 => 3591 +/- 5ppm
=> 3519ppm +/- 58ppm

Using the last 4 measurements, mean loss is 3596, and the std is 218. => Loss = 3600+/-200ppm