Jennie W, Sina K, Jim W,

We made good progress today. There was a factor of 4 that we had forgotten in the demodulation that you need to scale the final amplitude by to get the Vpp. Once we put this in we get ~100% for the reference interferometer and 76% for the measurement interferometer.

We debugged the demodulation calculation by turning off the signal input to the REF A IFO and then looking at what heterodyne amplitude it calculated when we injected a signal of 2Vpp into the H1:SPI-H23_IFO_REF_A_DEMOD_SIG filter bank.

See the photo showing the injected signal calibrated into volts in yellow, in purple the amplitude calculated as A = sqrt( I^2 + Q^2), where I and Q are the output of the demodulator, and in red is the out amplitude after multiplying by a factor of 4.

I put this calibration factor into all four H1:SPI-H23_IFO_{REF,MEAS}_{A,B}_HETAMP filter banks as cal_demod in FM0.

We also measured the dark offsets for the four PDs and two QPDs. We did this with the shutter closed. From the input counts, the QPD B segments look a lot noisier than the QPD A segments so I wonder if we are getting scattered light from main IFO beam.

I might redo this dark offset test with the JAC unlocked or with the PSL shuttered in order to verify this. It might also explain why we occasionally get the efficiency calculation of the reference interferometer coming out to 101% if we have stray light on one or more PDs.

The calibration factors and new dark offsets were accpted in SDF.

One of the nights this week we will start our program of calibration measurements using the ISI sensors to calibrate the SPI sensors.