By mingyuan, tara
We built a simple voltage summing circuit for adding DC level to the pzt. This circuit allows us to fine tune the inteferometer's differential arm length, so that we can operate at the fringe's maximum slope. Then we checked the peaks we observed from last time. It turned out to be harmonics from the common mode from driving.
The circuit schematic is shown below. The result Vout = Vin1 + Vin2.
The adding circuit is used as shown in the schematic (highlighted in yellow.)
*Later, we can use this summing circuit in a feedback control loop for locking the interferometer.
Then we used this circuit in the setup and repeat the measurement to check the peaks we observed last time. With the same setup, we observed the peaks again, but they probably are harmonics from 4Hz from common mode motion which was not perfectly cancelled.
We repeated the measurement again with 0.7 Hz driving, and the peaks disappeared. The signal between driving and not driving the arms are very similar. The shape of the PSD changes slightly because of the lower amplitude of the driving signal, as we low pass the signal at 0.1 Hz.
We do need a seismic isolation and vacuum chamber. Right now, sound from people speaking in the lab can disturb the measurement.
a few things we have to consider soon, before we use the maraging steel blades pulled down by a mass block in the experiment.
1) how should we push the blades? capacitor plate? magnetic coil?
2) When can we move and get a better table, so that we can decide on seismic isolation stage.
3) We have to start looking for vacuum bell jar for the experiment.
4) lock the interferometer?
5) will we get an npro laser for the experiment?