With Hirata-san.

• Using the horizontal fishng rods I moved the IP close to the setpoint.
• The GAS filters were already close to the setpoint.
• I open the vacuum chamber and aligned the collimator such that the beam reached the suspended mirror close to the centre.
• The I aligned the receiving optics such  that the beams reached both QPDs.
• I made sure the beam in the length sensing path went through the lens at the centre.

Tomorrow I will check the position of the micrometers and aim to set the lenth sensing QPD in a suitable place with respect to the lens.

Hirata-san checked the new screw system for locking the suspended breadboard.

• I moved the vertical micrometer stages to around 6 mm, which is close to their midrange and adjusted the two folding mirrors for the beams reach the QPD centers.
• I set the length sensing QPD at the appropriate position with respect to the lens:
  • I applied white noise actuation to TM-P and observed the amplitude of the 0.843 Hz resonance peak in the amplitude spectral density of the LEN VER  channel.
  • I normalized the channel values at the resonance with TILT VER in order to cancel out variations in TM-P actuation at each ASD measurement.
  • The plot shows the values before and after normalization.

As can be seen in the plot, the position of the length sensing QPD that minimizes the coupling from TM-P is at 8.50 mm. The ASD plot shows that the LEN VER (in blue) is at the noise floor level at such position.

Calibration of the oplev QPD readout in terms of the beam displacement

Today I used Miyo-kun's script to acquire the data. The current location of the data is 

/opt/rtcds/userapps/release/vis/common/scripts/autocommissioning/oplev/data/

The files are

SR2_TM_OPLEV_LEN_HOR.txt  SR2_TM_OPLEV_LEN_VER.txt  SR2_TM_OPLEV_TILT_HOR.txt  SR2_TM_OPLEV_TILT_VER.txt

I'll analyze the data and post the results later.

I analyzed  the calibration data.

The results are shown in the following table:

Observations:

• The linear ranges for the Tilt QPD are larger than those for the length QPD.
• The readout of the QPDs is not in units of counts. Counts refers to the DAC and ADC. I call the QPD readout units QPD displacement units or QPD-du.
• I fitted the data in Excel and not with the script provided in the medm screen because I wanted to choose the data points considered to be within the linear range and report the size of the range.

Using Fabian's data measured in 17614, I've obtained the calibration factors as follows.
Calibration notebooks can be found in /kagra/Dropbox/Subsystems/VIS/vis_commissioning/sr2/notebook/calibration/ 

LEN_HOR:
calibration factor: -115.477 µm/d.u.
linear range (5% nonlinearity):  ±67.785 µm

LEN_VER:
calibration factor: -106.598 µm/d.u.
linear range (5% nonlinearity): ±62.733 µm

TILT_HOR:
calibration factor: -706.673 µm/d.u.
linear range (5% nonlinearity): ±407.397 µm

TILT_VER:
calibration factor: -606.410 µm/d.u.
linear range (5% nonlinearity): ±338.377 µm

These calibration factors are implemented in K1:VIS-SR2_TM_OPLEV_{TILT, LEN}_{VER, HOR}_GAIN.