In the past, when heating up the OM2 heater, we have noticed that the low frequency sensitivity improves, for example alog 78652.

I wanted to make this comparison again, but we have seen that the squeezing performance can be variable, so I first chose to compare a no squeezing time with OM2 hot and cold.

It's also important to note that the calibration has likely changed with the hot OM2. Some of that can be corrected with the TDCFs. However, we saw that the required SRCL offset to minimize SRC detuning with OM2 hot was significantly different, alog 86737. This means that the sensing function is probably significantly different, causing some change in the calibration that is not compensated. We didn't take any calibration measurements with hot OM2, so we have no idea how much or how to compensate the calibration change.

With OM2 hot, the coherence of DARM with SRCL and MICH increased, although SRCL can explain most of the excess noise between the two times. Interestingly, the coherence of DARM with jitter decreased with OM2 hot. There is no significant change in the coherence with PRCL.

Here is a comparison of the cold and hot OM2 times, using GDS CALIB STRAIN CLEAN.

I performed a simple coherence subtraction of SRCL alone, and SRCL and MICH together. I checked that there is no significant coherence between SRCL and MICH.

Given the possible issue with the calibration, I am not certain how comparable the low frequency noise is. There is a small increase in the noise up to 30 Hz with OM2 hot, even with the above subtractions applied.