Summary:

This isn't meant to be a serious budget, mainly it was to force myself to write the code for generating this more easily in the future.

Details:

• DARM OLTF model from here was used to undo the loop to convert the in-loop measurement to a free-running estimate.
• The AS55 PD channels were whitened to reduce the effect of ADC noise.
• To measured channel was 'C1:LSC-DARM_IN1_DQ'.
  • Some care needs to be taken when applying the conversion from counts to meters using the sensing element measured here.
  • This is because the sensing matrix measurement was made using the response in the channel 'C1:LSC-AS55_Q_ERR_DQ'.
  • Between 'C1:LSC-DARM_IN1_DQ' and 'C1:LSC-AS55_Q_ERR_DQ' there is a scalar gain of 1e-4, and a z:p = 20:0 filter.
  • These have to be corrected for when undoing the loop, since the measurement point is 'C1:LSC-DARM_IN1_DQ'. 
• The "Dark noise" trace was measured with the PSL shutter closed, but all CDS filters up to 'C1:LSC-DARM_IN1_DQ' enabled as they were when the DARM measurement was taken.
• It would be interesting to see what the budget looks like once the DARM loop gain has been turned down a bit, some low-pass filtering is enabled, and the vertex DoFs are transitioned to 1f control which is hopefully lower noise.