NAOJ GW Elog Logbook 3.2
I checked the first measurement of the shinkosha 7 with s polarization at the input,
As shown in figure 1 there are some vertical stripes present in the measurement.
I tuned both the hwp and qwp in the injection and found out that when injecting s polarization, the p polarization readout is minimized for hwp = 0.1 deg instead of previously 1.3 deg.
Then, I also added beam dump to catch the PSD reflections and a small wall to isolate the imaging unit from the injection part.
The beam dump were removed because they are supposed to be used for visible light...
In any case the good news is that we can recognize similar patterns to the previous measurement with tilted beam.
Finally I restarted the s polarization measurement.
I had a look at the normalized Is and Ip data.
As seen in figures 1 and 2 which show respectively the s and p polarizations normalized intensities the stripes are mainly present in s polarization.
This was not the case for the previous measurements (see figures 3 and 4) were stripes were actually visibles in both s and p polarizations...
Also it seems that p polarization is saturating..
I have now taken 3 measurements with s polarization at the input that saturated the lockin amplifier..
It seems that we can really easily saturates the p polarization.
Indeed, it is connected to the old lockin amplifier where the range (0 to 1 V) is changed depending on the sensitivity setting we are using.
Now I'm injecting about 160 uW of power but when doing the measurement with s polarization it seems that the p polarization power changes by more than a factor 14...
I'm starting hopefully the last measurement with s polarization at the input where the sensitivity of the old lockin is set to 100 mV despite the value at the center being 0.2 mV.
It would be convenient to have a new lockin amplifier to avoid this issue...