With Hirata-san.

See pictures in SRM Remedying Work album.

Length QPD position along the optic axis

• We applied a sinusoidal function at 200 mHz to TM-Y.
• We measured amplitude spectral densities (ASD) of the four QPD readout channel for different positions of the QPD along the optic axis. We used a resolution of 30 mHz.
• As can be seen in the Fig. 1, the position that minimizes the readout in LEN HOR is 3 mm and we set the QPD at such a position. The data is in the spreadsheet attached.
• Figs. 2 and 3 show examples of the ASD for 3 and 3.91 mm respectively.

QDP readout calibration in terms of its displacement

• The data is in the spreasheet attached.
• The attached plots only show the data in the linear range. Plots with the whole datasets are in the attached spreadsheet.
• In ndscope style notation, the channel names used are K1: VIS-SRM_TM_OPLEV_{LEN,TILT}_{HOR,VER}_IN1.
• The unit name du stands for "displacement units".