As a temporary measure, I multiplied with a factor of 100 some amplification factors in two of the oplev medm screen. This with the aim to be able to see clearly where the oplev dot indicator is on the screen:

• K1:VIS-SRM_TM_OPLEV_TILT_VER_GAIN: 0.655 ⇒ 65.5
• K1:VIS-SRM_TM_OPLEV_TILT_HOR_GAIN: 0.712 ⇒ 71.2
• K1:VIS-SRM_TM_OPLEV_LEN_VER_GAIN: 0.108 ⇒ 10.8
• K1:VIS-SRM_TM_OPLEV_LEN_HOR_GAIN: 0.111 ⇒ 11.1

I did not commit these changes in the SDF.

Today I continued aligning the oplev optics.

Yesterday, after putting the breadboards with the optical components in place, it was relatively easy to get the light onto the QPD. This afternoon, however, I checked the position of the reflection point on the SRM mirror. It was too far away from the center. It was very close to the edge of the small SRM mirror. Then, I did the following:

• I moved the collimator to a different positon on the breadboard, and adjusted its tip and tilt, until the incoming beam was reflected close to the center of the SRM mirror and the reflected beam went out from the chamber close to the center of the output viewport.
• I adjusted the fist folding mirror in order to get the light onto the tilt QPD.
• I used the diffuser disc on the lens holder to make sure the beam for the length QPD went through the centre of the lens. The lens holder has adjustments for this purpose.
• I adjusted the second folding mirror to get the light onto the length sensing QPD.
• I used the micrometer nobs for each QPD to adjust their positions finely.

Tomorrow I aim to check the position of the length sensing QPD with respect to the lens, and calibrate the readout of the QDPs in terms of displacement. We should also build a cover.

Today I checked whether the length sensing QPD is in a suitable position with respect to the lens. I applied a sinusoidal actuation at 200 mHz in TM-Y and checked the ouput in the length sensing QPD. There was a relatively small coupling. I moved the QDP along the optic axis to see whether the coupling incresed or decreased, but it seemed to remain the same. I'll continue with this test tomorrow.

With Hirata-san. 

The details of the work here briefly described will be given later. 

• We did some measurements to decide the most suitable position of the length sensing QDP with respect to the lens. 
• We calibrated the output of the length sensing QDP with respect to its displacement the vertical direction. 

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".

With the calibration factors obtained, I put followings

K1:VIS-SRM_TM_OPLEV_LEN_VER_GAIN: 1/7.39*1000 = 135.318 [um/counts]

K1:VIS-SRM_TM_OPLEV_LEN_HOR_GAIN: 1/6.37*1000 = 148.599 [um/counts]

K1:VIS-SRM_TM_OPLEV_TILT_VER_GAIN: 1/1.3*1000 = 749.230 [um/counts]

K1:VIS-SRM_TM_OPLEV_TILT_HOR_GAIN: 1/1.22*1000 = 819.670 [um/counts]

which would calibrate K1:VIS-SRM_TM_OPLEV_{LEN, TILT}_{VER, HOR}_OUT to the beamspot positions at the QPD planes, in microns.

Using old length data from 7952, I obtained the OPLEV2EUL matrix as shown in Fig. 1. To reproduce, consult Eqn. (20) in JGW-T2112874 or visit the notebook in /kagra/Dropbox/Subsystems/VIS/vis_commissioning/srm/notebook/sensing_matrices/optical_lever.ipynb

I reverted the actuation matrix EUL2OSEM to 0.25s (for L) and 1s and -1s for (P and Y) and measure transfer functions. The readouts show a very high noise floor which is normal given the optical lever isn't covered with windshields. Nevertheless, Diagonalization was straightforward. And I obtained SENSALIGN matrix as shown in Fig. 2. Transfer functions measurements are shown in the following figures. Yaw transfer function plots were missing due to some unknown bugs, I will have to measure them again later. Nevertheless, the coupling ratios P/Y and L/Y are at the 1e-4 level at yaw resonances (Fig. 5).

Note that the matrices have very low commitments, as I might intercalibrate them with IP readouts. Also, I have not probably L2P coupling as I will use the IP to do so but I am doing minor adjustments at the IP level. But sanity check shows good inter-calibration with the IP.

I just added a new column to the table writing explicitly the size of the linear range: